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Designing an antenna for the 5000m band
Back in December I posted a question about ways to receive LF/VLF radio signals. Based on the suggestions made by a number of people here I decided to use my existing Heathkit Mohican receiver and add this upconverter kit from Jackson Harbor: http://jacksonharbor.home.att.net/lfconv.htm The kit arrived and was half assembled before I turned on the Mohican, its first power-up in some years; the horrible squeal that erupted from the speaker put a bit of a damper on things. It now appears that replacing the two output transistors (Germanium, no less!) with NTE102As from Mouser will fix that, so I'm thinking about an antenna that might be a little more snesitive to LF signals than the Mohican's built-in whip. Along those lines, I have a couple of (what I hope are) simple questions that I'm hoping someone can help me get started with. First, the need for impedance matching between an antenna and a receiver. My understanding is that a resonant halfwave dipole will have an impedance around 73 Ohms; unfortunately, unless I can obtain research funding from the just-passed Congressional Economic Stimulus bill I'm going to have trouble paying for 2.5km of copper wire, some towers, a crateload or two of porcelain insulators,and the land to build it on. (Hey, I promise to dump it back into the economy ASAP. Really! grin!) So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? I've done Google seaarches and read what seemed like the relevant sections of the 2004 ARRL Radio Handbook and their Antenna Book; unfortunately, most authors restrict their discussion to quarter- wave or longer antennae. Any starting points, hints, or references on impedance calculations for less-than-1/10-wavelength antennas will be appreciated. My other question has to do with how to interpret signal strength. The first "standard reference" transmitter I'll be attempting to receive will be WWVB out of Fort Collins, Colorado (60kHz/5000m). Per the NIST documentation at: NIST Special Publication 250-67: NIST Time and Frequency Radio Stations: WWV, WWVH, and WWVB http://ts.nist.gov/MeasurementServices/Calibrations/ Upload/SP250-67.pdf figure 4.5 seems to say that I could reasonably expect to see a signal of at least 100uV/m. Does this mean that I should expect to see 100uV from any one-meter hunk of wire strung out horizontally in the optimum direction? Or is there something more subtle going on I need to be aware of? Frank McKenney -- One of the ways to give the impression of an aesthetic performance to those lacking the organ of taste is indeed to put into a work of art the political, religious, or other extraneous satisfactions popular with one or another audience. Particularly, of course, if strongly held. -- Robert Conquest, "The Dragons of Expectation" -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) |
Designing an antenna for the 5000m band
On Mon, 16 Feb 2009 22:22:20 -0600, Frnak McKenney
wrote: First, the need for impedance matching between an antenna and a receiver. My understanding is that a resonant halfwave dipole will have an impedance around 73 Ohms; unfortunately, unless I can obtain research funding from the just-passed Congressional Economic Stimulus bill I'm going to have trouble paying for 2.5km of copper wire, some towers, a crateload or two of porcelain insulators,and the land to build it on. (Hey, I promise to dump it back into the economy ASAP. Really! grin!) So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? Hi Frank, One doesn't try. The simple solution is the conventional one - you use a tuner. The tuner provides the matching (providing it has sufficient inductance and capacitance - you will have to investigate designs) and adjacent signal rejection (which could seriously de-sense your received signals). Your antenna doesn't need to be very big, but it might help to have it very remote, if there are noise sources nearby (like motors, aquarium heaters, bottle style TVs, ...); and the line sufficiently choked. A good ground too, tying into the service ground through a separate wire to reduce coupling of noise from shared grounds. This last may introduce a ground loop if your Mohican is so vintage as to have had relaxed design standards. A little research online reveals it is battery operable. You may want to fully exercise that option. 73's Richard Clark, KB7QHC |
Designing an antenna for the 5000m band
"Frnak McKenney" http://ts.nist.gov/MeasurementServic...d/SP250-67.pdf ** Just how big is this file - eh ?? Why did you limit replies to ONE newsgroup while posting to TWO ??? What sort to total ****ING ASSHOLE are you ???? You ****ing ASININE YANK ****- head. ...... Phil |
Designing an antenna for the 5000m band
Hi, Phil. Thanks for responding.
On Tue, 17 Feb 2009 22:18:50 +1100, Phil Allison wrote: "Frnak McKenney" http://ts.nist.gov/MeasurementServic...d/SP250-67.pdf ** Just how big is this file - eh ?? Multiple megabytes: too large to paste the text into a newsgroup article, and I didn't think that appending it as an attachment would be appropriate. If you're limited to a dial-up connection, I can see that the size might be a problem. I could download a copy for you and forward it via e-mail if you think that would be any easier. ....Interesting. When I access a copy this morning, Adobe Reader 7.0 fetches _something_, but when I try to "Save a Copy" I get an I/O error pop-up, and Reader's Find command gets hung at about page 17. This is the same file I had no problems running a Find all the way through (several times) last night... wish I had saved a copy then (ain't hindsight wonderful? grin!). Would you like for me to forward a copy to you once I'm able to get a complete one? Frank McKenney -- "Provide me with ships or proper sails for the celestial atmosphere and there will be men there, too, who do not fear the appalling distance" -- Johannes Kepler -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) |
Designing an antenna for the 5000m band
"Frnak McKenney" Hi, Phil. Thanks for responding. ** Go to hell - asshole http://ts.nist.gov/MeasurementServic...d/SP250-67.pdf ** Just how big is this file - eh ?? Multiple megabytes: ** Then why not ****ing WARN people ?? ASSHOLE !! If you're limited to a dial-up connection, ** Not the case and 100% IRRELEVANT !! ASSHOLE !! Would you like for me to forward a copy to you once I'm able to get a complete one? ** Go shove it UP YOUR ARSE !! Why did you limit replies to ONE newsgroup while posting to TWO ??? ASSHOLE !!! ..... Phil |
Designing an antenna for the 5000m band
In article , Frnak McKenney wrote:
Back in December I posted a question about ways to receive LF/VLF radio signals. Based on the suggestions made by a number of people here I decided to use my existing Heathkit Mohican receiver and add this upconverter kit from Jackson Harbor: http://jacksonharbor.home.att.net/lfconv.htm The kit arrived and was half assembled before I turned on the Mohican, its first power-up in some years; the horrible squeal that erupted from the speaker put a bit of a damper on things. It now appears that replacing the two output transistors (Germanium, no less!) with NTE102As from Mouser will fix that, so I'm thinking about an antenna that might be a little more snesitive to LF signals than the Mohican's built-in whip. Along those lines, I have a couple of (what I hope are) simple questions that I'm hoping someone can help me get started with. First, the need for impedance matching between an antenna and a receiver. My understanding is that a resonant halfwave dipole will have an impedance around 73 Ohms; unfortunately, unless I can obtain research funding from the just-passed Congressional Economic Stimulus bill I'm going to have trouble paying for 2.5km of copper wire, some towers, a crateload or two of porcelain insulators,and the land to build it on. (Hey, I promise to dump it back into the economy ASAP. Really! grin!) So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? I've done Google seaarches and read what seemed like the relevant sections of the 2004 ARRL Radio Handbook and their Antenna Book; unfortunately, most authors restrict their discussion to quarter- wave or longer antennae. Any starting points, hints, or references on impedance calculations for less-than-1/10-wavelength antennas will be appreciated. My other question has to do with how to interpret signal strength. The first "standard reference" transmitter I'll be attempting to receive will be WWVB out of Fort Collins, Colorado (60kHz/5000m). Per the NIST documentation at: NIST Special Publication 250-67: NIST Time and Frequency Radio Stations: WWV, WWVH, and WWVB http://ts.nist.gov/MeasurementServices/Calibrations/ Upload/SP250-67.pdf figure 4.5 seems to say that I could reasonably expect to see a signal of at least 100uV/m. Does this mean that I should expect to see 100uV from any one-meter hunk of wire strung out horizontally in the optimum direction? Or is there something more subtle going on I need to be aware of? Frank McKenney http://www.frontiernet.net/~jadale/Loop.htm |
Designing an antenna for the 5000m band
Hey, his name is Frnak, doesn't he have enough troubles already?
|
Designing an antenna for the 5000m band
On Feb 16, 11:22*pm, Frnak McKenney
wrote: Back in December I posted a question about ways to receive LF/VLF radio signals. *Based on the suggestions made by a number of people here I decided to use my existing Heathkit Mohican receiver and add this upconverter kit from Jackson Harbor: *http://jacksonharbor.home.att.net/lfconv.htm The kit arrived and was half assembled before I turned on the Mohican, its first power-up in some years; the horrible squeal that erupted from the speaker put a bit of a damper on things. *It now appears that replacing the two output transistors (Germanium, no less!) *with NTE102As from Mouser will fix that, so I'm thinking about an antenna that might be a little more snesitive to LF signals than the Mohican's built-in whip. Along those lines, I have a couple of (what I hope are) simple questions that I'm hoping someone can help me get started with. First, the need for impedance matching between an antenna and a receiver. *My understanding is that a resonant halfwave dipole will have an impedance around 73 Ohms; unfortunately, unless I can obtain research funding from the just-passed Congressional Economic Stimulus bill I'm going to have trouble paying for 2.5km of copper wire, some towers, a crateload or two of porcelain insulators,and the land to build it on. *(Hey, I promise to dump it back into the economy ASAP. *Really! *grin!) So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? I've done Google seaarches and read what seemed like the relevant sections of the 2004 ARRL Radio Handbook and their Antenna Book; unfortunately, most authors restrict their discussion to quarter- wave or longer antennae. *Any starting points, hints, or references on impedance calculations for less-than-1/10-wavelength antennas will be appreciated. My other question has to do with how to interpret signal strength. The first "standard reference" transmitter I'll be attempting to receive will be WWVB out of Fort Collins, Colorado (60kHz/5000m). Per the NIST documentation at: * NIST Special Publication 250-67: NIST Time and Frequency Radio * * * * * * Stations: WWV, WWVH, and WWVB *http://ts.nist.gov/MeasurementServices/Calibrations/ * * * * * * Upload/SP250-67.pdf figure 4.5 seems to say that I could reasonably expect to see a signal of at least 100uV/m. *Does this mean that I should expect to see 100uV from any one-meter hunk of wire strung out horizontally in the optimum direction? Or is there something more subtle going on I need to be aware of? Frank McKenney A field strength measured in Volts/meter is just that, but the problem getting the energy out of the air and into a receiver. A short linear antenna has a very low radiation resistance ( 1 ohm) which is a poor match to a practical transmission line, whose characteristic impedance is typically 1000's of times larger. The radiation resistance of an antenna is the component of its complex impedance that is associated with the power captured. Poor impedance matching is equivalent to low energy efficiency, in this case very low. One solution is to use a small circular loop antenna whose low radiation resistance can be increased by adding turns. Balanis (Antenna Theory Analysis & Design (1997), p.209) gives a formula for the radiation resistance of a loop smaller than 1/25 wavelength: R = 20 * pi^2 * (C/L)^4 * N^2 ohms where C is the circumference of the loop, L is the wavelength and N is the number of turns. Better still is to use a ferrite loop antenna. You may be able to get one out of an old AM radio and adapt it to your receiver. The resulting formula is identical to the above, multiplied by the relative permeability of the core, u (SQUARED !), so you can use a very small-diameter loop and/or fewer turns, getting improved selectivity and sensitivity (i.e. high Q) in a tuned circuit: R = 20 * pi^2 * (C/L)^4 * N^2 * u^2 ohms -- Joe |
Designing an antenna for the 5000m band
On Feb 16, 11:22*pm, Frnak McKenney
wrote: Back in December I posted a question about ways to receive LF/VLF radio signals. *Based on the suggestions made by a number of people here I decided to use my existing Heathkit Mohican receiver and add this upconverter kit from Jackson Harbor: *http://jacksonharbor.home.att.net/lfconv.htm The kit arrived and was half assembled before I turned on the Mohican, its first power-up in some years; the horrible squeal that erupted from the speaker put a bit of a damper on things. *It now appears that replacing the two output transistors (Germanium, no less!) *with NTE102As from Mouser will fix that, so I'm thinking about an antenna that might be a little more snesitive to LF signals than the Mohican's built-in whip. Along those lines, I have a couple of (what I hope are) simple questions that I'm hoping someone can help me get started with. First, the need for impedance matching between an antenna and a receiver. *My understanding is that a resonant halfwave dipole will have an impedance around 73 Ohms; unfortunately, unless I can obtain research funding from the just-passed Congressional Economic Stimulus bill I'm going to have trouble paying for 2.5km of copper wire, some towers, a crateload or two of porcelain insulators,and the land to build it on. *(Hey, I promise to dump it back into the economy ASAP. *Really! *grin!) So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? I've done Google seaarches and read what seemed like the relevant sections of the 2004 ARRL Radio Handbook and their Antenna Book; unfortunately, most authors restrict their discussion to quarter- wave or longer antennae. *Any starting points, hints, or references on impedance calculations for less-than-1/10-wavelength antennas will be appreciated. My other question has to do with how to interpret signal strength. The first "standard reference" transmitter I'll be attempting to receive will be WWVB out of Fort Collins, Colorado (60kHz/5000m). Per the NIST documentation at: * NIST Special Publication 250-67: NIST Time and Frequency Radio * * * * * * Stations: WWV, WWVH, and WWVB *http://ts.nist.gov/MeasurementServices/Calibrations/ * * * * * * Upload/SP250-67.pdf figure 4.5 seems to say that I could reasonably expect to see a signal of at least 100uV/m. *Does this mean that I should expect to see 100uV from any one-meter hunk of wire strung out horizontally in the optimum direction? Or is there something more subtle going on I need to be aware of? Frank McKenney -- * * One of the ways to give the impression of an aesthetic performance * * to those lacking the organ of taste is indeed to put into a work * * of art the political, religious, or other extraneous satisfactions * * popular with one or another audience. *Particularly, of course, if * * strongly held. * -- Robert Conquest, "The Dragons of Expectation" -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) A field strength measured in Volts/meter is just that, but the problem getting the energy out of the air and into a receiver. A short linear antenna has a very low radiation resistance ( 1 ohm) which is a poor match to a practical transmission line, whose characteristic impedance is typically 1000's of times larger. The radiation resistance of an antenna is the component of its complex impedance that is associated with the power captured. Poor impedance matching is equivalent to low energy efficiency, in this case very low. One solution is to use a small circular loop antenna whose low radiation resistance can be increased by adding turns. Balanis (Antenna Theory Analysis & Design (1997), p.209) gives a formula for the radiation resistance of a loop smaller than 1/25 wavelength: R = 20 * pi^2 * (C/L)^4 * N^2 ohms where C is the circumference of the loop, L is the wavelength and N is the number of turns. Better still is to use a ferrite loop antenna. You may be able to get one out of an old AM radio and adapt it to your receiver. The resulting formula is identical to the above, multiplied by the relative permeability of the core, u (SQUARED !), so you can use a very small-diameter loop and/or fewer turns, getting improved selectivity and sensitivity (i.e. high Q) in a tuned circuit: R = 20 * pi^2 * (C/L)^4 * N^2 * u^2 ohms -- Joe |
Designing an antenna for the 5000m band
On Mon, 16 Feb 2009 22:22:20 -0600, Frnak McKenney
wrote: So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? Antennas can be modeled by various NEC based programs. For example: http://home.ict.nl/~arivoors/ http://www.eznec.com http://www.nittany-scientific.com Note that the common "atomic clock" gets its time from WWVB at 60KHz (about 5000 meters) using a tiny loop antenna. Huge antennas are not required for many application. http://www.mas-oy.com/data/MAS_docu_AR.htm http://www.leapsecond.com/pages/sony-wwvb/ Also, search Google for LOWFER. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Designing an antenna for the 5000m band
On Mon, 16 Feb 2009 22:22:20 -0600, Frnak McKenney wrote:
Back in December I posted a question about ways to receive LF/VLF radio signals. Based on the suggestions made by a number of people here I decided to use my existing Heathkit Mohican receiver and add this upconverter kit from Jackson Harbor: http://jacksonharbor.home.att.net/lfconv.htm The kit arrived and was half assembled before I turned on the Mohican, its first power-up in some years; the horrible squeal that erupted from the speaker put a bit of a damper on things. It now appears that replacing the two output transistors (Germanium, no less!) with NTE102As from Mouser will fix that, so I'm thinking about an antenna that might be a little more snesitive to LF signals than the Mohican's built-in whip. Along those lines, I have a couple of (what I hope are) simple questions that I'm hoping someone can help me get started with. First, the need for impedance matching between an antenna and a receiver. My understanding is that a resonant halfwave dipole will have an impedance around 73 Ohms; unfortunately, unless I can obtain research funding from the just-passed Congressional Economic Stimulus bill I'm going to have trouble paying for 2.5km of copper wire, some towers, a crateload or two of porcelain insulators,and the land to build it on. (Hey, I promise to dump it back into the economy ASAP. Really! grin!) So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? I've done Google seaarches and read what seemed like the relevant sections of the 2004 ARRL Radio Handbook and their Antenna Book; unfortunately, most authors restrict their discussion to quarter- wave or longer antennae. Any starting points, hints, or references on impedance calculations for less-than-1/10-wavelength antennas will be appreciated. My other question has to do with how to interpret signal strength. The first "standard reference" transmitter I'll be attempting to receive will be WWVB out of Fort Collins, Colorado (60kHz/5000m). Per the NIST documentation at: NIST Special Publication 250-67: NIST Time and Frequency Radio Stations: WWV, WWVH, and WWVB http://ts.nist.gov/MeasurementServices/Calibrations/ Upload/SP250-67.pdf figure 4.5 seems to say that I could reasonably expect to see a signal of at least 100uV/m. Does this mean that I should expect to see 100uV from any one-meter hunk of wire strung out horizontally in the optimum direction? Or is there something more subtle going on I need to be aware of? Why do you want a good impedance match? Why don't you want to use a loop antenna? At 5000m, atmospheric noise is very strong -- it would certainly overwhelm any thermal noise that you'd receive if you did make a 1/2 wave dipole (don't forget that your towers need to be at least 2500m tall to get close to the ideal). Getting an appropriate impedance match is mostly about maximizing your signal compared with your receiver's internal noise; the strong atmospheric noise makes this less necessary. This atmospheric noise also makes really efficient receiving antennas rather unimportant. You want a good fraction of a wavelength for _transmitting_, but it really doesn't make much difference for _receiving_. The two common receiving antennas that I know of at that sort of frequency are tuned loops and capacitive whips. A loop can be fairly small -- my understanding (which I've never tested, YMMV) is that one square meter is plenty. Loops are nice because you can tune them, so they give you some additional selectivity on your receiver front end. You can impedance match the loop to your receiver, but most of the impedance your receiver sees will come from the wire in the loop, not the radiation resistance of the loop. Loops are also somewhat directive, which helps to reduce the total static received, and if done correctly (google "shielded loop") they can be arranged to reject sky waves (I _think_ by polarization, but I'm not sure). A capacitive whip is just a 1m long wire whip (like a coat hanger or welding rod) feeding some high impedance amplifier like a JFET (or a toob, if you want to be picturesque). Put the active element right at the base of the wire for best signal. It's inherently wide band, and hard to keep it from being so, so if you have some local interference it'll kill your signal (my first try at these didn't work in my shop because of a nearby electric fence transformer, but it worked fine at the end-user's more-urban location). -- http://www.wescottdesign.com |
Designing an antenna for the 5000m band
On Feb 16, 11:22*pm, Frnak McKenney
wrote: Back in December I posted a question about ways to receive LF/VLF radio signals. *Based on the suggestions made by a number of people here I decided to use my existing Heathkit Mohican receiver and add this upconverter kit from Jackson Harbor: *http://jacksonharbor.home.att.net/lfconv.htm The kit arrived and was half assembled before I turned on the Mohican, its first power-up in some years; the horrible squeal that erupted from the speaker put a bit of a damper on things. *It now appears that replacing the two output transistors (Germanium, no less!) *with NTE102As from Mouser will fix that, so I'm thinking about an antenna that might be a little more snesitive to LF signals than the Mohican's built-in whip. Along those lines, I have a couple of (what I hope are) simple questions that I'm hoping someone can help me get started with. First, the need for impedance matching between an antenna and a receiver. *My understanding is that a resonant halfwave dipole will have an impedance around 73 Ohms; unfortunately, unless I can obtain research funding from the just-passed Congressional Economic Stimulus bill I'm going to have trouble paying for 2.5km of copper wire, some towers, a crateload or two of porcelain insulators,and the land to build it on. *(Hey, I promise to dump it back into the economy ASAP. *Really! *grin!) So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? I've done Google seaarches and read what seemed like the relevant sections of the 2004 ARRL Radio Handbook and their Antenna Book; unfortunately, most authors restrict their discussion to quarter- wave or longer antennae. *Any starting points, hints, or references on impedance calculations for less-than-1/10-wavelength antennas will be appreciated. My other question has to do with how to interpret signal strength. The first "standard reference" transmitter I'll be attempting to receive will be WWVB out of Fort Collins, Colorado (60kHz/5000m). Per the NIST documentation at: * NIST Special Publication 250-67: NIST Time and Frequency Radio * * * * * * Stations: WWV, WWVH, and WWVB *http://ts.nist.gov/MeasurementServices/Calibrations/ * * * * * * Upload/SP250-67.pdf figure 4.5 seems to say that I could reasonably expect to see a signal of at least 100uV/m. *Does this mean that I should expect to see 100uV from any one-meter hunk of wire strung out horizontally in the optimum direction? Or is there something more subtle going on I need to be aware of? Frank McKenney A field strength measured in Volts/meter is just that, but the problem getting the energy out of the air and into a receiver. A short linear antenna has a very low radiation resistance ( 1 ohm) which is a poor match to a practical transmission line, whose characteristic impedance is typically 1000's of times larger. The radiation resistance of an antenna is the component of its complex impedance that is associated with the power captured. Poor impedance matching is equivalent to low energy efficiency, in this case very low. One solution is to use a small circular loop antenna whose low radiation resistance can be increased by adding turns. Balanis (Antenna Theory Analysis & Design (1997), p.209) gives a formula for the radiation resistance of a loop smaller than 1/25 wavelength: R = 20 * pi^2 * (C/L)^4 * N^2 ohms where C is the circumference of the loop, L is the wavelength and N is the number of turns. Better still is to use a ferrite loop antenna. You may be able to get one out of an old AM radio and adapt it to your receiver. The resulting formula is identical to the above, multiplied by the relative permeability of the core, u (SQUARED !), so you can use a very small-diameter loop and/or fewer turns, getting improved selectivity and sensitivity (i.e. high Q) in a tuned circuit: R = 20 * pi^2 * (C/L)^4 * N^2 * u^2 ohms -- Joe |
Designing an antenna for the 5000m band
"Phil Allison" wrote in message ... "Frnak McKenney" http://ts.nist.gov/MeasurementServic...d/SP250-67.pdf ** Just how big is this file - eh ?? Why did you limit replies to ONE newsgroup while posting to TWO ??? What sort to total ****ING ASSHOLE are you ???? You ****ing ASININE YANK ****- head. ..... Phil Uh-oh! Looks like somebody isn't getting enough fiber! |
Designing an antenna for the 5000m band
On Mon, 16 Feb 2009 22:22:20 -0600, Frnak McKenney wrote:
Back in December I posted a question about ways to receive LF/VLF radio signals. Based on the suggestions made by a number of people here I decided to use my existing Heathkit Mohican receiver and add this upconverter kit from Jackson Harbor: http://jacksonharbor.home.att.net/lfconv.htm The kit arrived and was half assembled before I turned on the Mohican, its first power-up in some years; the horrible squeal that erupted from the speaker put a bit of a damper on things. It now appears that replacing the two output transistors (Germanium, no less!) with NTE102As from Mouser will fix that, so I'm thinking about an antenna that might be a little more snesitive to LF signals than the Mohican's built-in whip. Along those lines, I have a couple of (what I hope are) simple questions that I'm hoping someone can help me get started with. First, the need for impedance matching between an antenna and a receiver. My understanding is that a resonant halfwave dipole will have an impedance around 73 Ohms; unfortunately, unless I can obtain research funding from the just-passed Congressional Economic Stimulus bill I'm going to have trouble paying for 2.5km of copper wire, some towers, a crateload or two of porcelain insulators,and the land to build it on. (Hey, I promise to dump it back into the economy ASAP. Really! grin!) So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? I've done Google seaarches and read what seemed like the relevant sections of the 2004 ARRL Radio Handbook and their Antenna Book; unfortunately, most authors restrict their discussion to quarter- wave or longer antennae. Any starting points, hints, or references on impedance calculations for less-than-1/10-wavelength antennas will be appreciated. My other question has to do with how to interpret signal strength. The first "standard reference" transmitter I'll be attempting to receive will be WWVB out of Fort Collins, Colorado (60kHz/5000m). Per the NIST documentation at: NIST Special Publication 250-67: NIST Time and Frequency Radio Stations: WWV, WWVH, and WWVB http://ts.nist.gov/MeasurementServices/Calibrations/ Upload/SP250-67.pdf figure 4.5 seems to say that I could reasonably expect to see a signal of at least 100uV/m. Does this mean that I should expect to see 100uV from any one-meter hunk of wire strung out horizontally in the optimum direction? Or is there something more subtle going on I need to be aware of? This may be a duplicate answer: I _know_ I wrote one, but it seems to have fallen into the bit-bucket. In short: For receiving you don't need to couple well enough to the ether to overwhelm the receiver's noise with the Faintest Possible Signal. You only need to overwhelm the receiver's noise with atmospheric noise. Given the amount of atmospheric noise at 60kHz, that ain't hard. When you get to the point where you hook up the antenna to the rig and you heard static over the noise of the receiver, you know your antenna is good enough. (Transmitting is a different story, but try transmitting at 60kHz and after the FCC gets done with you antenna size will be the least of your worries.) Whazza matta widda loop? They work fine, they provide some welcome selectivity (well, at 60kHz one may provide _too much_ selectivity), they're easy to construct, they're reputed to reject sky waves -- what more could you want? If you don't want to use a loop, the last time I did anything at MF a short (1m) whip going to a JFET source follower was considered the bee's knees to solve this sort of problem. The whip will pick up atmospheric noise just as well as it'll pick up the intended signal, the JFET will impedance match from that low-capacity whip to your receiver input (I assume, I don't know what the nominal input impedance of your rig is), and all will be well. -- http://www.wescottdesign.com |
Designing an antenna for the 5000m band
On Feb 18, 8:05*am, "Sal M. Onella"
wrote: "Phil Allison" wrote in message ... "Frnak McKenney" *http://ts.nist.gov/MeasurementServic...d/SP250-67.pdf ** Just how big is this file * * - *eh *?? Why did you limit replies to *ONE *newsgroup while posting *to TWO * ??? What sort to total *****ING *ASSHOLE *are you * ???? You ****ing *ASININE *YANK *****- head. ..... * Phil Uh-oh! *Looks like somebody isn't getting enough fiber! Someone woke up on the wrong side of NOBODY again.... |
Designing an antenna for the 5000m band
On Feb 16, 11:22*pm, Frnak McKenney
wrote: Back in December I posted a question about ways to receive LF/VLF radio signals. *Based on the suggestions made by a number of people here I decided to use my existing Heathkit Mohican receiver and add this upconverter kit from Jackson Harbor: *http://jacksonharbor.home.att.net/lfconv.htm The kit arrived and was half assembled before I turned on the Mohican, its first power-up in some years; the horrible squeal that erupted from the speaker put a bit of a damper on things. *It now appears that replacing the two output transistors (Germanium, no less!) *with NTE102As from Mouser will fix that, so I'm thinking about an antenna that might be a little more snesitive to LF signals than the Mohican's built-in whip. Along those lines, I have a couple of (what I hope are) simple questions that I'm hoping someone can help me get started with. First, the need for impedance matching between an antenna and a receiver. *My understanding is that a resonant halfwave dipole will have an impedance around 73 Ohms; unfortunately, unless I can obtain research funding from the just-passed Congressional Economic Stimulus bill I'm going to have trouble paying for 2.5km of copper wire, some towers, a crateload or two of porcelain insulators,and the land to build it on. *(Hey, I promise to dump it back into the economy ASAP. *Really! *grin!) So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? I've done Google seaarches and read what seemed like the relevant sections of the 2004 ARRL Radio Handbook and their Antenna Book; unfortunately, most authors restrict their discussion to quarter- wave or longer antennae. *Any starting points, hints, or references on impedance calculations for less-than-1/10-wavelength antennas will be appreciated. My other question has to do with how to interpret signal strength. The first "standard reference" transmitter I'll be attempting to receive will be WWVB out of Fort Collins, Colorado (60kHz/5000m). Per the NIST documentation at: * NIST Special Publication 250-67: NIST Time and Frequency Radio * * * * * * Stations: WWV, WWVH, and WWVB *http://ts.nist.gov/MeasurementServices/Calibrations/ * * * * * * Upload/SP250-67.pdf figure 4.5 seems to say that I could reasonably expect to see a signal of at least 100uV/m. *Does this mean that I should expect to see 100uV from any one-meter hunk of wire strung out horizontally in the optimum direction? Or is there something more subtle going on I need to be aware of? Frank McKenney A field strength measured in 100 uV/meter is just that, but the problem getting the energy out of the air and into a receiver. A short linear antenna has a very low radiation resistance ( 1 ohm) which is a poor match to a practical transmission line, whose characteristic impedance is typically 1000's of times larger. The radiation resistance of an antenna is the component of its complex impedance that is associated with the power captured. Balanis (Antenna Theory Analysis & Design (1997), p.137) gives a formula for the radiation resistance of a short dipole: R = 80 * pi^2 * (W/L)^2 ohms where W is the length of the antenna and L is the wavelength. The value for a monopole is roughly half as much again. Why do you request a non-loop antenna? A small circular loop antenna also has a low radiation resistance but it can be increased by adding turns. Balanis (p.209) gives a formula for the radiation resistance of a small loop: R = 20 * pi^2 * (C/L)^4 * N^2 ohms where C is the circumference of the loop, L is the wavelength and N is the number of turns. Better still is to use a ferrite loop antenna. You may be able to get one out of an old AM radio and adapt it to your receiver. The resulting formula is identical to the above, multiplied by the relative permeability of the core, u (SQUARED !), so you can use a very small-diameter loop and/or fewer turns, getting improved selectivity and sensitivity (i.e. high Q) in a tuned circuit: R = 20 * pi^2 * (C/L)^4 * N^2 * u^2 ohms -- Joe |
Designing an antenna for the 5000m band
Richard,
Thank you for posting back. On Mon, 16 Feb 2009 23:07:37 -0800, Richard Clark wrote: On Mon, 16 Feb 2009 22:22:20 -0600, Frnak McKenney wrote: First, the need for impedance matching between an antenna and a receiver. --snip complaint about the size/cost of 60kHz h-w diploes grin!-- So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? One doesn't try. So Yoda was right: "Do, or do not. There is no 'try'." grin! What has puzzled me is that I have run across designs that use (e.g.) a JFET isolation amplifier hooked to a whip or hunk-o-wire with the statement (or implication) that this is done to ",atch the antenna's impedance". So I;ve been trying to figure out how to calculate/estimate what it would be, without much success. The simple solution is the conventional one - you use a tuner. The tuner provides the matching (providing it has sufficient inductance and capacitance - you will have to investigate designs) and adjacent signal rejection (which could seriously de-sense your received signals). I imagine that the inductance of a 6' extension cord (not plugged in, just dangling from a planter hook grin!) is down in the uH-or-less range, which would mean that most of the "tuning" inductance would have to be supplied to achieve 60kHz. I have this image of a big (tens of mH) inductor in series with a moderate capacitor and my (electrically) short wire; all of the surrounding EM sets the electroncs in the wire to dancing, but the series RC blocks those which are wiggling "off-key" (e.g. not dancing at the "proper" rate of 60kHz). Your antenna doesn't need to be very big, but it might help to have it very remote, if there are noise sources nearby (like motors, aquarium heaters, bottle style TVs, ...); and the line sufficiently choked. A good ground too, tying into the service ground through a separate wire to reduce coupling of noise from shared grounds. Well, there's no question that I have EM in the area. I hooked my DVM -- set to ACV -- between the radiator and my 6' extension cord; would you believe 8-10V??!! Not much current, though: feed it through a 1k resistor and measure the voltage across it, suddenly it's down in the mV range. grin! ... This last may introduce a ground loop if your Mohican is so vintage as to have had relaxed design standards. A little research online reveals it is battery operable. You may want to fully exercise that option. The Mohican came with two 12V power "modules" which plug into the back of the unit. The AC power module has a transformer with a 12V-12V center-tapped secondary, which is good, but then they run the line voltage out of the module and down into the receiver's volume control's on/off switch. The module's 12V power and 120V switching connections are done through a 9-pin tube socket with mating connector/cable; remember those? grin! 73's Thanks for the hepl. Frank -- There is one thing even more vital to science than intelligent methods; and that is, the sincere desire to find out the truth, whatever that may be. -- Charles Sanders Pierce -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) |
Designing an antenna for the 5000m band
On Tue, 17 Feb 2009 13:56:38 GMT, GregS wrote:
In article , Frnak McKenney wrote: Back in December I posted a question about ways to receive LF/VLF radio signals. --snip-- ... I'm thinking about an antenna that might be a little more snesitive to LF signals than the Mohican's built-in whip. http://www.frontiernet.net/~jadale/Loop.htm Thanks for the link. Firefox claims I visited it recently, but I apparently forgot to save it into my "VLF Antenna" folder. It's there _now_! grin! Frank -- "Wisdom lies in taking everything with good humor and a grain of salt." -- George Santayana -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) |
Designing an antenna for the 5000m band
Jeff,
Thanks for the reply. On Tue, 17 Feb 2009 08:36:23 -0800, Jeff Liebermann wrote: On Mon, 16 Feb 2009 22:22:20 -0600, Frnak McKenney wrote: So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? Antennas can be modeled by various NEC based programs. For example: http://home.ict.nl/~arivoors/ http://www.eznec.com http://www.nittany-scientific.com Note that the common "atomic clock" gets its time from WWVB at 60KHz (about 5000 meters) using a tiny loop antenna. Huge antennas are not required for many application. http://www.mas-oy.com/data/MAS_docu_AR.htm http://www.leapsecond.com/pages/sony-wwvb/ That's what I keep reading; any caution you hear coming from me is based on years spent in close association with Murphy. grin! I'm a long-time devotee of the Divide'n'Conquer(tm) school of analysis and troubleshooting. This only works well when one is familiar with the appropriate problem-partitioning tools and has experience using them; as it is, I'm trying to acquire the knowledge that will let me know why things didn't work when they don't work as expected. grin! Also, search Google for LOWFER. Thanks. I did see the phrase, but forgot to write it down; after some hours searching the 'Web and reading it all seems to run together. grin! Frank -- "When the government fears the people, there is liberty. When the people fear the government, there is tyranny." -- Thomas Jefferson -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) |
Designing an antenna for the 5000m band
Tim,
Thanks for the response. On Tue, 17 Feb 2009 11:02:42 -0600, Tim Wescott wrote: On Mon, 16 Feb 2009 22:22:20 -0600, Frnak McKenney wrote: Back in December I posted a question about ways to receive LF/VLF radio signals. --snip-- First, the need for impedance matching between an antenna and a receiver. --snip-- So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? --snip-- Why do you want a good impedance match? Because I'm trying to snatch a signal that I have no experience with "out of the aether", a signal that has to somehow excite an antenna, feed into an upconverter, arrive at my receiver, and produce some specific identifying evidence that I'm detecting the signal I hope it will rather than (say) reporting that my neighbor is using his electric razor. grin! Each of these pieces (except perhaps the Mohican) are untested (by me), and I don't have any tools that will help me easily distinguish between (say) a bad upconverter, a poor antenna, or excessive noise. Like many such situations, I'll know if I _succeed_, but if I don't there won't be any clear indicators to help me figure out _which_ piece of the puzzle isn't fitting properly. In short, anything that sounds like it might affect my results is of interest to me. Why don't you want to use a loop antenna? It's a question of time and effort: it looks like it will take me less of each to test the "wire" first. If it succeeds, I'm done; if not, I can start experimenting with loops. Which is, of course, a variant on one of my favorite puzzles: How do you allocate your resources when you don't yet know what you're doin... er, "under conditions of less-than-perfect information"? grin! At 5000m, atmospheric noise is very strong -- it would certainly overwhelm any thermal noise that you'd receive if you did make a 1/2 wave dipole (don't forget that your towers need to be at least 2500m tall to get close to the ideal). Getting an appropriate impedance match is mostly about maximizing your signal compared with your receiver's internal noise; the strong atmospheric noise makes this less necessary. Yeah. All that, plus the funding. But mostly the funding. grin! This atmospheric noise also makes really efficient receiving antennas rather unimportant. You want a good fraction of a wavelength for _transmitting_, but it really doesn't make much difference for _receiving_. Which may well be true, but it seems puzzling. Why would it not be important to deliver as much of the induced electron movement to a receiver as possible? The two common receiving antennas that I know of at that sort of frequency are tuned loops and capacitive whips. A loop can be fairly small -- my understanding (which I've never tested, YMMV) is that one square meter is plenty. Loops are nice because you can tune them, so they give you some additional selectivity on your receiver front end. You can impedance match the loop to your receiver, but most of the impedance your receiver sees will come from the wire in the loop, not the radiation resistance of the loop. Talking about "radiation resistance" in a receiver antenna also feels a bit odd. ... Loops are also somewhat directive, which helps to reduce the total static received, and if done correctly (google "shielded loop") they can be arranged to reject sky waves (I _think_ by polarization, but I'm not sure). Yes. I'm reading up on loops so I have an alternative available in caseXXXXXXX_when_ something goes wrong. A capacitive whip is just a 1m long wire whip (like a coat hanger or welding rod) feeding some high impedance amplifier like a JFET (or a toob, if you want to be picturesque). Put the active element right at the base of the wire for best signal. It's inherently wide band, and hard to keep it from being so, so if you have some local interference it'll kill your signal This is the direction I'm starting in. ... (my first try at these didn't work in my shop because of a nearby electric fence transformer, but it worked fine at the end-user's more-urban location). Gack! I don't suppose it used an old Model-T spark coil, or a buzzer-and transformer equivalent? I remember in my youth (Dirt(tm) _had_ been invented, but it was still considered cutting-edge technology grin!) just how badly one could mess up AM BCB reception with a string of those Christmas tree bulbs with built-in bimetallic-switch flashers. Frank -- You'll never learn to do anything well until you're willing to accept that you'll do it badly at first. --Anonymous -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) |
Designing an antenna for the 5000m band
Hi, Tim. grin!
On Wed, 18 Feb 2009 02:03:44 -0600, Tim Wescott wrote: On Mon, 16 Feb 2009 22:22:20 -0600, Frnak McKenney wrote: Back in December I posted a question about ways to receive LF/VLF radio signals. --snip-- First, the need for impedance matching between an antenna and a receiver. --snip-- This may be a duplicate answer: I _know_ I wrote one, but it seems to have fallen into the bit-bucket. Received and replied to, but your rephrasing is also appreciated. In short: For receiving you don't need to couple well enough to the ether to overwhelm the receiver's noise with the Faintest Possible Signal. You only need to overwhelm the receiver's noise with atmospheric noise. Given the amount of atmospheric noise at 60kHz, that ain't hard. When you get to the point where you hook up the antenna to the rig and you heard static over the noise of the receiver, you know your antenna is good enough. Well, I'm getting static with the built-in whip. On the other hand, I haven't hooked up the downconverter yet. (Transmitting is a different story, but try transmitting at 60kHz and after the FCC gets done with you antenna size will be the least of your worries.) Yeah, but the picture of all the local "Atomic Clocks" changing at once _is_ rather appealing. grin! Whazza matta widda loop? They work fine, they provide some welcome selectivity (well, at 60kHz one may provide _too much_ selectivity), they're easy to construct, they're reputed to reject sky waves -- what more could you want? Laziness? A Scot's instinct to thrift? grin! If you don't want to use a loop, the last time I did anything at MF a short (1m) whip going to a JFET source follower was considered the bee's knees to solve this sort of problem. The whip will pick up atmospheric noise just as well as it'll pick up the intended signal, the JFET will impedance match from that low-capacity whip to your receiver input (I assume, I don't know what the nominal input impedance of your rig is), and all will be well. Well, from my point of view you just justified the effort you put into this second post; you got me digging into the Mohinca's manual which lists sensitivity (10uV) and Selectivity ("3 kc wide at 6 db down"[sic]), but no specific antenna impedance. According to the _schematic_, the two screw-lug connections on the rear of the chassis are "HI-Z" and "GND" (apparently the Heathkit designers thought of a "short wire" antenna as high impedance as well). The HI-Z line runs through a "12uuF"[sic] to the whip, and then both are connected through a 22pF capacitor to the Main Tuning and Antenna Trim capacitors. Fortunately the LF upconverter comes (IIRC) with 1MHz and 4MHz crystals, so I won't be trying to force a 60kHz signal past those itty-bitty little capacitors. grin! Frank -- Ninety-Ninety Rule of Project Scheduling: The first ninety percent of the task takes ninety percent of the time, and the last ten percent takes the other ninety percent. -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) |
Designing an antenna for the 5000m band
Joe,
Thanks for replying. I wan't entirely certain which of the four I should respond to, but I'm assuming this was the vinfal version. On Wed, 18 Feb 2009 06:11:29 -0800 (PST), J.A. Legris wrote: On Feb 16, 11:22*pm, Frnak McKenney wrote: Back in December I posted a question about ways to receive LF/VLF radio signals. --snip-- So any non-loop antenna I can construct will necessarily be a "short wire" or "electrically small" antenna (two useful search terms). But how does one go about calculating the impedance of a coat hanger or an extension cord ("short piece of wire")? --snip-- My other question has to do with how to interpret signal strength. --snip-- a signal of at least 100uV/m. *Does this mean that I should expect to see 100uV from any one-meter hunk of wire strung out horizontally in the optimum direction? Or is there something more subtle going on I need to be aware of? A field strength measured in 100 uV/meter is just that, but the problem getting the energy out of the air and into a receiver. Yes. It's not like I can just hang a bucket out the window and bring it back full of electrons wiggling at just the right speed. grin! A short linear antenna has a very low radiation resistance ( 1 ohm) which is a poor match to a practical transmission line, whose characteristic impedance is typically 1000's of times larger. The radiation resistance of an antenna is the component of its complex impedance that is associated with the power captured. Balanis (Antenna Theory Analysis & Design (1997), p.137) gives a formula for the radiation resistance of a short dipole: R = 80 * pi^2 * (W/L)^2 ohms where W is the length of the antenna and L is the wavelength. The value for a monopole is roughly half as much again. Um... 1.5 * 80 * (%pi^2) * (1/5000)^2 is... 471 micro-Ohms? That 's pretty low; why would anyone match that to a JFET input? Why do you request a non-loop antenna? I started there, ran into some questions, and wanted to clear up the confusion in my own head before moving any further. It's not as though I'm prejudiced against them; heck, some of my best friends have radios with loop antennae. grin! ... A small circular loop antenna also has a low radiation resistance but it can be increased by adding turns. Balanis (p.209) gives a formula for the radiation resistance of a small loop: R = 20 * pi^2 * (C/L)^4 * N^2 ohms where C is the circumference of the loop, L is the wavelength and N is the number of turns. Better still is to use a ferrite loop antenna. You may be able to get one out of an old AM radio and adapt it to your receiver. The resulting formula is identical to the above, multiplied by the relative permeability of the core, u (SQUARED !), so you can use a very small-diameter loop and/or fewer turns, getting improved selectivity and sensitivity (i.e. high Q) in a tuned circuit: R = 20 * pi^2 * (C/L)^4 * N^2 * u^2 ohms Oddly enough, I now have ten old transistor radios that I picked up at FrostFest a few weekends back for $1 each. I was looking for ferrite and wide-ratio tuning capacitors, as they seem to be in scarce supply these days. I don't know where today's kids are getting their crystal radio parts from these days; it certainly isn't Radio Shack. Frank -- "A man should never be ashamed to own that he has been in the wrong, which is but saying, in other words, that he is wiser today than yesterday." -- Jonathan Swift -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) |
Designing an antenna for the 5000m band
On Wed, 18 Feb 2009 12:06:09 -0600, Frnak McKenney
wrote: What has puzzled me is that I have run across designs that use (e.g.) a JFET isolation amplifier hooked to a whip or hunk-o-wire with the statement (or implication) that this is done to ",atch the antenna's impedance". Hi Frank, Matching provokes heated debates that in times past ran to 600+ postings - few knew what they were arguing (but enjoyed arguing nonetheless) and little was offered. A JFET at these frequencies does satisfy the naive requirements of "matching," but that giving you a reception solution doesn't always follow. So I;ve been trying to figure out how to calculate/estimate what it would be, without much success. The Mohican schematic says quite planely Hi-Z input. This is borne out by the antenna connection feeding a tank circuit in the front end where the input stage is fed from a low tap into a 470 Ohm resistor. This would be your JFET feed Z, but you could choose any suitable close value. As for the input Z, the JFET input resistance is perfectly capable of mismatching horribly high - although this is not about optimal power transfer at these impedance levels. What is at risk, is the JFET input capacitance which could present a low Z at some frequency. Naturally, you select your JFET against this to optimize. It will be in some ratio to the antenna capacitance (if it is bare, short wire) and that will establish the proportion of signal that gets in by divider action. I imagine that the inductance of a 6' extension cord (not plugged in, just dangling from a planter hook grin!) is down in the uH-or-less range, which would mean that most of the "tuning" inductance would have to be supplied to achieve 60kHz. I have this image of a big (tens of mH) inductor in series with a moderate capacitor and my (electrically) short wire; That is one way, other ways work too and are electrically equivalent. Loops help tune and match by a slightly more elaborate means, but still fairly holds to simple requirements. You don't need wire to build an inductor. At these frequencies you can use a capacitor in a Gyrator design. all of the surrounding EM sets the electroncs in the wire to dancing, but the series RC blocks those which are wiggling "off-key" (e.g. not dancing at the "proper" rate of 60kHz). And this responds to the filtering capacity (selection AND rejection). This is called "Q" which also serves the yeoman's task of matching as well (observe the input tank design for the conventional bands). Well, there's no question that I have EM in the area. I hooked my DVM -- set to ACV -- between the radiator and my 6' extension cord; would you believe 8-10V??!! Not much current, though: feed it through a 1k resistor and measure the voltage across it, suddenly it's down in the mV range. grin! Still a lot of power. However, those are probably 60Hz fields because DVMs rarely have the AC BW to go much above 1Khz. The Mohican came with two 12V power "modules" which plug into the back of the unit. The AC power module has a transformer with a 12V-12V center-tapped secondary, which is good, but then they run the line voltage out of the module and down into the receiver's volume control's on/off switch. The module's 12V power and 120V switching connections are done through a 9-pin tube socket with mating connector/cable; remember those? grin! Remembering isn't difficult. I broke into electronics through TV/Radio repair during high school. If I could fix it, I got paid. Anyway, power connections from that era brought "ground" notoriously close to lethal if you plugged the radio into the wall wrong. Some used AC noise reduction circuit design that could almost guarantee your chassis was floating at 70V if things went wrong. I had an ET striker (Navy parlance for a student electronics tech) who connected a TV antenna input to ground, and the insulation melted off of the wire in a heartbeat. This was in the day when we called TV power line interlock replacements "suicide adapters." 73's Richard Clark, KB7QHC |
Designing an antenna for the 5000m band
In article ,
Frnak McKenney wrote: Big Snip. Go find Radio-Electronics magazine for 1983, and read the five(?) articles by Ralph Burhans about receiving VLF. Mark Zenier Googleproofaddress(account:mzenier provider:eskimo domain:com) |
Designing an antenna for the 5000m band
On Feb 18, 3:12*pm, Richard Clark wrote:
On Wed, 18 Feb 2009 12:06:09 -0600, Frnak McKenney wrote: What has puzzled me is that I have run across designs that use (e.g.) a JFET isolation amplifier hooked to a whip or hunk-o-wire with the statement (or implication) that this is done to ",atch the antenna's impedance". Hi Frank, Matching provokes heated debates that in times past ran to 600+ postings - few knew what they were arguing (but enjoyed arguing nonetheless) and little was offered. A JFET at these frequencies does satisfy the naive requirements of "matching," but that giving you a reception solution doesn't always follow. So I;ve been trying to figure out how to calculate/estimate what it would be, without much success. The Mohican schematic says quite planely Hi-Z input. *This is borne out by the antenna connection feeding a tank circuit in the front end where the input stage is fed from a low tap into a 470 Ohm resistor. This would be your JFET feed Z, but you could choose any suitable close value. *As for the input Z, the JFET input resistance is perfectly capable of mismatching horribly high - although this is not about optimal power transfer at these impedance levels. *What is at risk, is the JFET input capacitance which could present a low Z at some frequency. *Naturally, you select your JFET against this to optimize. *It will be in some ratio to the antenna capacitance (if it is bare, short wire) and that will establish the proportion of signal that gets in by divider action. I imagine that the inductance of a 6' extension cord (not plugged in, just dangling from a planter hook grin!) is down in the uH-or-less range, which would mean that most of the "tuning" inductance would have to be supplied to achieve 60kHz. *I have this image of a big (tens of mH) inductor in series with a moderate capacitor and my (electrically) short wire; That is one way, other ways work too and are electrically equivalent. Loops help tune and match by a slightly more elaborate means, but still fairly holds to simple requirements. You don't need wire to build an inductor. *At these frequencies you can use a capacitor in a Gyrator design. all of the surrounding EM sets the electroncs in the wire to dancing, but the series RC blocks those which are wiggling "off-key" (e.g. *not dancing at the "proper" rate of 60kHz). And this responds to the filtering capacity (selection AND rejection). This is called "Q" which also serves the yeoman's task of matching as well (observe the input tank design for the conventional bands). Well, there's no question that I have EM in the area. I hooked my DVM -- set to ACV -- between the radiator and my 6' extension cord; would you believe 8-10V??!! Not much current, though: feed it through a 1k resistor and measure the voltage across it, suddenly it's down in the mV range. grin! Still a lot of power. *However, those are probably 60Hz fields because DVMs rarely have the AC BW to go much above 1Khz. The Mohican came with two 12V power "modules" which plug into the back of the unit. *The AC power module has a transformer with a 12V-12V center-tapped secondary, which is good, but then they run the line voltage out of the module and down into the receiver's volume control's on/off switch. *The module's 12V power and 120V switching connections are done through a 9-pin tube socket with mating connector/cable; remember those? *grin! Remembering isn't difficult. *I broke into electronics through TV/Radio repair during high school. *If I could fix it, I got paid. Anyway, power connections from that era brought "ground" notoriously close to lethal if you plugged the radio into the wall wrong. *Some used AC noise reduction circuit design that could almost guarantee your chassis was floating at 70V if things went wrong. I had an ET striker (Navy parlance for a student electronics tech) who connected a TV antenna input to ground, and the insulation melted off of the wire in a heartbeat. *This was in the day when we called TV power line interlock replacements "suicide adapters." 73's Richard Clark, KB7QHC Its not uncommon to have a high impedance input into a preamp. This is the one-size- fits-all approach. While its not good engineering for the purist it works quite well to make a casual user happy and may be the practical solution for even the professional installation.. Ive had some experience limited working with VLF and it always seemed the thing that made the difference between a good and bad VLF antenna was the quality of the ground network Jimmie |
Designing an antenna for the 5000m band
In article ,
Jim Thompson wrote: On Wed, 18 Feb 2009 20:57:00 GMT, (Mark Zenier) wrote: In article , Frnak McKenney wrote: Big Snip. Go find Radio-Electronics magazine for 1983, and read the five(?) articles by Ralph Burhans about receiving VLF. Mark Zenier Googleproofaddress(account:mzenier provider:eskimo domain:com) Is that set of articles available on the web? That'd be an interesting read. Some of them. I remember on of them coming up in a discussion in one of the radio newsgroups, and someone posted a URL. They are practical hobby stuff mostly. A VLF converter, how to match longwire antenna, an active whip antenna, a balanced loopstick. The most useful non-hobby one was how to derive time/frequency references from Loran-C. I'm reluctant to go to the effort because this was back in the era when R-E was paranoid about photocopying, with colored backgrounds for the figures and charts, and it would take a day or two to photoshop the scans so that they are of decent quality. Also, they were, near the end, one of the more Internet savvy publishers and there may still be somebody around to enforce their IP. Mark Zenier Googleproofaddress(account:mzenier provider:eskimo domain:com) |
Designing an antenna for the 5000m band
"Jim Thompson" wrote in message ... Is that set of articles available on the web? That'd be an interesting read. ...Jim Thompson The 5 parts were later combined into a separate reprint, sold by R-E. Sections for theory and circuits, construction, testing. Then building a passive tuner VLF-LF, and a final section on loop antennas. One of the five sections is a Loran-C receiver!! I have an original copy in perfect condition, 30 pages, glossy paper, copyright 1984 by Gernsback Publications, Inc. |
Designing an antenna for the 5000m band
On Thu, 19 Feb 2009 20:12:06 GMT, (Mark Zenier)
wrote: In article , Jim Thompson wrote: On Wed, 18 Feb 2009 20:57:00 GMT, (Mark Zenier) wrote: In article , Frnak McKenney wrote: Big Snip. Go find Radio-Electronics magazine for 1983, and read the five(?) articles by Ralph Burhans about receiving VLF. Mark Zenier Googleproofaddress(account:mzenier provider:eskimo domain:com) Is that set of articles available on the web? That'd be an interesting read. Some of them. I remember on of them coming up in a discussion in one of the radio newsgroups, and someone posted a URL. They are practical hobby stuff mostly. A VLF converter, how to match longwire antenna, an active whip antenna, a balanced loopstick. The most useful non-hobby one was how to derive time/frequency references from Loran-C. I'm reluctant to go to the effort because this was back in the era when R-E was paranoid about photocopying, with colored backgrounds for the figures and charts, and it would take a day or two to photoshop the scans so that they are of decent quality. Also, they were, near the end, one of the more Internet savvy publishers and there may still be somebody around to enforce their IP. Mark Zenier Googleproofaddress(account:mzenier provider:eskimo domain:com) Send them to me. I can work magic with a scanner ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine Sometimes I even put it in the food |
Designing an antenna for the 5000m band
On Wed, 18 Feb 2009 12:12:53 -0800, Richard Clark wrote:
On Wed, 18 Feb 2009 12:06:09 -0600, Frnak McKenney wrote: What has puzzled me is that I have run across designs that use (e.g.) a JFET isolation amplifier hooked to a whip or hunk-o-wire with the statement (or implication) that this is done to ",atch the antenna's impedance". Matching provokes heated debates that in times past ran to 600+ postings - few knew what they were arguing (but enjoyed arguing nonetheless) and little was offered. What I think I'm looking for would be a point of reference that would let me, if not exactly evaluate the facets of such an argument, at least be a foundation for forming a testable opinion of my own. A JFET at these frequencies does satisfy the naive requirements of "matching," but that giving you a reception solution doesn't always follow. In my current state of ignorance of the subject, this sentence has the appearance of a Zen koan: something that sounds non-sensical at first glance, but which, after sufficient time and effort studying, will undoubtedly become so blindingly obvious as to appear trivial. Thank you... I think. grin! So I;ve been trying to figure out how to calculate/estimate what it would be, without much success. The Mohican schematic says quite planely Hi-Z input. This is borne out by the antenna connection feeding a tank circuit in the front end where the input stage is fed from a low tap into a 470 Ohm resistor. ... Ah! You have a Mohican? Or just access to the manual? Mine is missing, burioed somewhere in my basement; I was fortunate enough to locate a copy of a GC-1A PDF some kind soul posted online. ... This would be your JFET feed Z, but you could choose any suitable close value. As for the input Z, the JFET input resistance is perfectly capable of mismatching horribly high - although this is not about optimal power transfer at these impedance levels. What is at risk, is the JFET input capacitance which could present a low Z at some frequency. Naturally, you select your JFET against this to optimize. It will be in some ratio to the antenna capacitance (if it is bare, short wire) and that will establish the proportion of signal that gets in by divider action. I imagine that the inductance of a 6' extension cord (not plugged in, just dangling from a planter hook grin!) is down in the uH-or-less range, which would mean that most of the "tuning" inductance would have to be supplied to achieve 60kHz. I have this image of a big (tens of mH) inductor in series with a moderate capacitor and my (electrically) short wire; That is one way, other ways work too and are electrically equivalent. Loops help tune and match by a slightly more elaborate means, but still fairly holds to simple requirements. You don't need wire to build an inductor. At these frequencies you can use a capacitor in a Gyrator design. "Gyrator"? I thought that was the rooftop dance that follows an antenna adjustment in mid-thunderstorm. grin! Google led me to the AAVSO site (www.aavso.org) which led me to the Yahoo VLF_Group. Aaaaaaaaaaaaaaauuuuuuuggggh! A circuit that can replace capacitors or inductors? My first reaction is "technology at a level indistunguisable from black magic". I don't think I'm in Kansas any more. (On the other hand, I have lots more toys to play with. grin!) all of the surrounding EM sets the electroncs in the wire to dancing, but the series RC blocks those which are wiggling "off-key" (e.g. not dancing at the "proper" rate of 60kHz). And this responds to the filtering capacity (selection AND rejection). This is called "Q" which also serves the yeoman's task of matching as well Um. I don't think I ever got past the simplistic "High Q = Good, Low Q = Evil" stage. Looking back, I can now see cases where an excessively high Q might be... counterproductive, but as always, it depends on what one means by "high" or "low" in a given context. Noted as something else I need to review and not depend on instinct for. ... (observe the input tank design for the conventional bands). Of the five bands (A-E, SW3 positions 5-1), the only one which seems different is "E", with an additional 130pF cap between the antenna and the tank circuit. Is that what you're referring to? --snip-- ... The module's 12V power and 120V switching connections are done through a 9-pin tube socket with mating connector/cable; remember those? grin! Remembering isn't difficult. I broke into electronics through TV/Radio repair during high school. If I could fix it, I got paid. _You_ got _paid_!?? grin! Woody Maiden, WA4GMV, ran a radio/TV shop near my home and didn't object to someone hanging around and watching over his shoulder in the afternoons, but he was a bit concerned about his liability insurance. (Don't know why. I didn't get zapped by a "discharged" CRT until my college years. grin!) Anyway, power connections from that era brought "ground" notoriously close to lethal if you plugged the radio into the wall wrong. Some used AC noise reduction circuit design that could almost guarantee your chassis was floating at 70V if things went wrong. "We don' need no steeken' transformers!" I think I saw a 50C5 in one of my basement boxes a few months back. grin! I had an ET striker (Navy parlance for a student electronics tech) who connected a TV antenna input to ground, and the insulation melted off of the wire in a heartbeat. This was in the day when we called TV power line interlock replacements "suicide adapters." I learned about them from my father, a power company EE who wasn't above swapping the odd tube or building a color TV from a kit with my little sister's help. 73's Richard Clark, KB7QHC * * * If you're getting bored, please feel free to skip the following; on the other hand, someone with access to a GC-1 manual might enjoy my story... A few months back I pulled my old Mohican out from under a pile of magazines and blew the dust off it. It had been buried so long that I had forgotten why I never built an outdoor antenna for it or showed it to my nephews an nieces; I remembered the moment I powered it on: there was a loud buzz coming from the speaker. This wasn't _hum_ mind you, which even when loud has a sort of even-ness to it; this was an intense, jagged, and metallic "I'm shredding your speaker cone and I don't care!" kind of low-frequency buzz. Worse, it went _away_ when I turned the volume _up_, and reappeared when I turned it (the volume control) down. I was able to isolate it to the audio section by unsoldering the capacitor connecting the volume control wiper to the base of the first audio stage. It went away (blessed relief!), and when I hooked up a RadioShack "utility" amplifier to the volume control wiper the sound was clear and crisp. I considered this A Clue. grin! NTE listed their NTE102A as a replacement for the Mohican's 2N407s... at nearly $7 each (apparently Germanium is on the Endangered Elements List). I replaced all three AF transistors, and the audio level was much better than it has been. Unfortunately, the BUZZZZZ was still present, and also louder. I did notice that turning the ANL ON (diode and resistor connected between the base of X7 and ground) eliminated it. I tried all sorts of things. I jumpered the volume control wiper to ground to make sure the resistance arc hadn't cracked, leaving the wiper floating near its low end. I tried swapping the transistors around. I tried paralleling the electrolytics I could reach, but no luck. As you've seen (or know personally) the Mohican's IF and AF stages are all on one printed circuit board which is bolted down to the chaissis with ?2-40 machine screws around its border. I couldn't see much of the underside of the AF section of this board because my vision -- and fingers -- were blocked by a large AF transformer, so I unbolted it and let it hang free (but not shorting anything; thank &deity for stiff transformer leads). With that pushed out of the way I could see all three AF transistor sockets and even reach them with my test leads. I jumpered a 100uF electrolytic from the chassis to the emitter pin of X7, the AF stage 1 transistor, parallelling it with the existing 150uF emitter bypass capacitor (C55(?)), and a miracle occurred: the buzz disappeared! I can't tell you how good it felt to hear normal-sounding hiss, static, and the odd "sqrgrl" coming out of the Mohican's speaker. No 150uF in the parts bin, so I wired two caps in parallel for a 147uF, shrink-wrapped them, unsoldered the decades-old 150uF and wired the glob-cap in its place. Didn't even burn my fingers in the confined spacegrin!. And then I turned it on. BZZZZZZZZZZZZZZ!! I'm sure you recall the feeling: "What did I do wrong?" Bad solder joint? No... Overheated the component? Not as far as I could tell. Dropped a solder glob across two traces frying by $7 transistors? No... in fact, although the buzz existed over a larger percentage of the volume control's span, the louder end of the audio worked just as it had before. My "proven cure" had made the problem slightly worse. It was late, I was tired, so I decided that, since my previous jumpering had created 250uF total, I needed to hit the problem with a bigger hammer: I jumpered in a _470uF_ this time. And the buzz went away. Again. Okay. Now I was _sure_ I had fixed the problem, so I unsoldered my obviously-too-clever glob-cap and soldered in the 470uF, this time triple-checking the polarity markings. I inspected the traces for possible solder bridges. I inspected the new solder joints under a large magnifier and wiggled the new leads; the joints looked good, so I hooked up the power supply again and turned it on. BZZZZZZZZZZZZZZ!! By now I was tired _and_ cranky, so I jumpered in the original decades-old 150uF cap. No buzz. At that point I had two options: go down in the basement and bring up a sledge hammer, or quit to go eat supper. It was a close call, but supper won out. There's something very weird about watching the news, eating supper, and looking over a schematic and trying to work what I was doing differently when it worked. If the emitter of X7 is wired to R37 and C55, and if the other ends of R37/C55 are wired to ground, how on Earth could a new capacitor jumpered from X7's emitter to the chassis cause different behavior from the _same_ capacitor soldered to a trace going to the same emitter and the PC board's ground trace? All I could think was "this makes no sense, but it does appear to be happening". R37/C55 were clearly grounded. The trace was unbroken. If they weren't grounded, I'd be getting _no_ audio. So how could _soldering_ to ground be any different from _jumpering_ to ground? Even stranger, how could a jumpered connection be _better_ than a soldered connection? * * * You've probably figured it out by now. The answer is that when I was jumpering, it was to the metal chassis; when I was soldering, it was to the PC board ground trace. The "ground" trace on this PC board includes a wide band around its outer edge; the strip makes contact with the chassis when the board is bolted down, creating a really solid round-the-board ground. Somehow, over the past half-century, the contact between the chassis and trace had become slightly less than perfectly conductive, and was "floating" in the Never-Never Land between zero and infinite resistance. Loosen all ten machine screws slightly, spray some contact cleaner in the extremely narrow gap, tighten the screws, and guess what? NO BUZZ! Re-mount the transformer(*). Reconnect C54 to the volume control wiper. Check for accidental shorts, dropped bits of solder and component leads, and make sure the transistors haven't fallen out of their sockets while I had the chassis upside down, Turn it on. STILL NO BUZZ! By then it was 2230, so I went to bed. Next step will be to improve the PC board/chassis contact by running a thin bit of fine steel wool around a bit to get rid of any residual crud; with luck, it'll be another couple of decades before this problem reappears. As for the 470uF capacitor, I think I'll leave it in place. The original is likely good, but 470uF should work as well, and all I need now is to have that portion of the trace lift off from the PC board due to overheating. * * * What's interesting here is the contrast between the schematic and reality. On paper, or on my CRT, those components were clearly connected to ground, and, had I hand-drawn my jumper wires, their wiring lines would have looked identical. It took me a long time to find the cause of the buzz because I was stuck thinking about the lines on the schematic, even though my hands were working on physical components, wires, and traces; how do you know when to stop trusting your compass and check it against the sun and stars? Definitely a "Learning Experience". grin! Anyway, thanks again for your comments. My head is about to explode from all the new ideas, but please don't take that amiss. If I don't expand it occasionally, it starts collapsing into a dull, super-dense mass (think neutron star grin!). (*) GlueStic(tm) is great for assembling hardware in confined quarters. It's much better than spit for making lockwashers and nuts stick to your fingertips so they don't drop off into the chassis interior. Frank -- "If language is not correct, then what is said is not what is meant; if what is said is not what is meant, then what ought to be done remains undone." -- Confucius -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) |
Designing an antenna for the 5000m band
On Sat, 21 Feb 2009 19:37:34 -0600, Frnak McKenney
wrote: Matching provokes heated debates that in times past ran to 600+ postings - few knew what they were arguing (but enjoyed arguing nonetheless) and little was offered. What I think I'm looking for would be a point of reference that would let me, if not exactly evaluate the facets of such an argument, at least be a foundation for forming a testable opinion of my own. Opinion is, after all, what powers the Internet. A JFET at these frequencies does satisfy the naive requirements of "matching," but that giving you a reception solution doesn't always follow. In my current state of ignorance of the subject, this sentence has the appearance of a Zen koan: something that sounds non-sensical at first glance, but which, after sufficient time and effort studying, will undoubtedly become so blindingly obvious as to appear trivial. Thank you... I think. grin! I could reduce it to the classic "take two aspirin and call me in the morning." Ah! You have a Mohican? Or just access to the manual? Mine is missing, burioed somewhere in my basement; I was fortunate enough to locate a copy of a GC-1A PDF some kind soul posted online. It didn't take much effort to scour the web for one (schematic). You don't need wire to build an inductor. At these frequencies you can use a capacitor in a Gyrator design. "Gyrator"? I thought that was the rooftop dance that follows an antenna adjustment in mid-thunderstorm. grin! Google led me to the AAVSO site (www.aavso.org) which led me to the Yahoo VLF_Group. Aaaaaaaaaaaaaaauuuuuuuggggh! A circuit that can replace capacitors or inductors? My first reaction is "technology at a level indistunguisable from black magic". I don't think I'm in Kansas any more. Gyrators have been around for a very long time, and can be found in a billion telephones, one probably within reach of you at the moment. They use telephones in Kansas don't they, Toto? You can build one with four components (none of them an inductor) to make an inductor more precisely than you could winding one. If you truly want to be overwhelmed with the dark arts, try googling for "magnetic amplifiers." (Art would go ballistic knowing such a topic was in practice looooong before he left second form.) No tubes, no transistors, and the orginal "solid state" design. As this may sound as if it wanders from the subject of RF, add the name Ernst F. W. Alexanderson to any search. (On the other hand, I have lots more toys to play with. grin!) all of the surrounding EM sets the electroncs in the wire to dancing, but the series RC blocks those which are wiggling "off-key" (e.g. not dancing at the "proper" rate of 60kHz). And this responds to the filtering capacity (selection AND rejection). This is called "Q" which also serves the yeoman's task of matching as well Um. I don't think I ever got past the simplistic "High Q = Good, Low Q = Evil" stage. Looking back, I can now see cases where an excessively high Q might be... counterproductive, but as always, it depends on what one means by "high" or "low" in a given context. Noted as something else I need to review and not depend on instinct for. ... (observe the input tank design for the conventional bands). Of the five bands (A-E, SW3 positions 5-1), the only one which seems different is "E", with an additional 130pF cap between the antenna and the tank circuit. Is that what you're referring to? I am merely pointing out the obvious application of a tapped inductor of the tuned front end serving as impedance match to an high-Z antenna (the topic of your choice). The schematic abounds in examples. One need only substitute values to serve the right frequency band - a simple exercise in reverse engineering employed since Hertz drew a spark across a gap at the base of a loop. If you're getting bored, please feel free to skip the following; on the other hand, someone with access to a GC-1 manual might enjoy my story... Yes, your story was/is classic with a beginning, middle, and end. Very few chroniclers here manage to write with as much clarity. (We get mostly cheesy attempts with "cliff hangers" serving as examples of neo-scholarly writing.) Your learning lesson of maintaining the chassis ground with the trace is classic too. The discovery of corrosion brings up the common practice of taking ALL the tubes out and putting them back in to solve problems. Tightening ALL screws is another hard learned lesson that bench techs either get or don't get. You probably could have got away with cheaper transistors by also substituting the bias diodes (56-7s) - but as events bore out, the transistors were good. If you note the difference between the base and emitter voltages, there is only about a tenth volt there. If I am to presume the diode call-out is for an 1N56, it is germanium too. What is more amazing is this wasn't about the decrepitude of the electrolytic capacitors which usually suffer with time if they are not used for a long while. 73's Richard Clark, KB7QHC |
Designing an antenna for the 5000m band
Jimmie,
Thank you for your comments. On Wed, 18 Feb 2009 13:19:12 -0800 (PST), JIMMIE wrote: On Feb 18, 3:12*pm, Richard Clark wrote: On Wed, 18 Feb 2009 12:06:09 -0600, Frnak McKenney wrote: What has puzzled me is that I have run across designs that use (e.g.) a JFET isolation amplifier hooked to a whip or hunk-o-wire with the statement (or implication) that this is done to ",atch the antenna's impedance". Hi Frank, Matching provokes heated debates that in times past ran to 600+ postings - few knew what they were arguing (but enjoyed arguing nonetheless) and little was offered. A JFET at these frequencies does satisfy the naive requirements of "matching," but that giving you a reception solution doesn't always follow. --snip-- Its not uncommon to have a high impedance input into a preamp. This is the one-size- fits-all approach. While its not good engineering for the purist it works quite well to make a casual user happy and may be the practical solution for even the professional installation.. Well, I think of myself as a "casual user", and _I'd_ like to be happy. grin! I don't mind throwing in a high-impedance (JFET) front end to my antenna simply on the basis that (a) people who seem to know what they're talking about recommend it and (b) I associate "high impedance" with "sensitive" (which seems like a desirable quality when you're working with microvolts). Someday, though, I'd like to have build up a framework in which _I_ can see why it's appropriate, or at least "does no harm". grin! My brother Bruce is working on the same problem from a slightly different angle; his experience is in software and digital stuff, and I find myself unintentionally assuming the role of "RF expert" without an EE degree or years of circuit design to back it up. Left to myself, I'm perfectly capable of pushing stuff around on the breadboard until it seems to work, but when I'm offering advice to someone else I'd prefer a better response to his questions than "someone else said so". grin! Ive had some experience limited working with VLF and it always seemed the thing that made the difference between a good and bad VLF antenna was the quality of the ground network Thanks for the suggestion. Do you think that my current "ground", a 30x60' 4-way pipe-loop network (mixed copper and cast iron) with thermal radiation elements might be... um, "less than satisfactory"? grin! Frank -- "What one writer can make in the solitude of one room is something no power can easily destroy." -- Salman Rushdie -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) |
Designing an antenna for the 5000m band
Mark,
Thank you for joining in. On Wed, 18 Feb 2009 20:57:00 GMT, Mark Zenier wrote: In article , Frnak McKenney wrote: Big Snip. And much appreciated by me and others. grin! Go find Radio-Electronics magazine for 1983, and read the five(?) articles by Ralph Burhans about receiving VLF. I ran across one article he wrote, in PDF format, but couldn't locate the articles. Have you seen them posted anywhere? Also, Dr. Barry Ornitz was kind enough to send me a PDF file describing two books available from the ARRL online store at http://www.arrl.org/: Mike Dennison and Jim Moritz: LF Today Peter Dodd: The Low Frequency Expermenter's Handbook He also took the time to offer a description of why a JFET input matches a high impedance. The words seem to fit together, but I'm still working on downconverting it to a frequency low enough for my brain to accept. grin! Frank -- ˙People demand freedom of speech to make up for the freedom of thought which they avoid.˙ -- Soren Kierkegaard -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) |
Designing an antenna for the 5000m band
On Feb 22, 11:57*am, Frnak McKenney
wrote: Mark, Thank you for joining in. On Wed, 18 Feb 2009 20:57:00 GMT, Mark Zenier wrote: In article , Frnak McKenney wrote: Big Snip. And much appreciated by me and others. grin! Go find Radio-Electronics magazine for 1983, and read the five(?) articles by Ralph Burhans about receiving VLF. I ran across one article he wrote, in PDF format, but couldn't locate the articles. Have you seen them posted anywhere? Also, Dr. *Barry Ornitz was kind enough to send me a PDF file describing two books available from the ARRL online store athttp://www.arrl.org/: * Mike Dennison and Jim Moritz: LF Today * Peter Dodd: The Low Frequency Expermenter's Handbook He also took the time to offer a description of why a JFET input matches a high impedance. *The words seem to fit together, but I'm still working on downconverting it to a frequency low enough for my brain to accept. *grin! Frank -- * ˙People demand freedom of speech to make up for the freedom of * *thought which they avoid.˙ -- Soren Kierkegaard -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) The first time I tried to dabble with VLF the rx front end I found from an university paper was nothing more than a triode(probably 1/2 a 12AX7) amp using a couple of TV horizontal osc coils as the tank circuit. After breadboarding the rx up on an old TV chassis I kept it around for a few years soon loosing interest in the CW and man made data transmisssions. There seem to be quite a few naturally occuring sources of RF in that band that sound interesting, some almost musical. Jimmie |
Designing an antenna for the 5000m band
On Sat, 21 Feb 2009 22:13:47 -0800, Richard Clark wrote:
On Sat, 21 Feb 2009 19:37:34 -0600, Frnak McKenney wrote: --snip-- Google led me to the AAVSO site (www.aavso.org) which led me to the Yahoo VLF_Group. Aaaaaaaaaaaaaaauuuuuuuggggh! A circuit that can replace capacitors or inductors? My first reaction is "technology at a level indistunguisable from black magic". I don't think I'm in Kansas any more. Gyrators have been around for a very long time, and can be found in a billion telephones, one probably within reach of you at the moment. They use telephones in Kansas don't they, Toto? You can build one with four components (none of them an inductor) to make an inductor That's what the man said... I saw the schematics for Gyrators I-III, and I need to go back and re-read the decriptive text. more precisely than you could winding one. That doesn't take much. I've had days recently where I felt like I could wind a mile of wire around a ferrite rod and _still_ not make an inductor. grin! If you truly want to be overwhelmed with the dark arts, try googling for "magnetic amplifiers." (Art would go ballistic knowing such a topic was in practice looooong before he left second form.) No tubes, no transistors, and the orginal "solid state" design. As this may sound as if it wanders from the subject of RF, add the name Ernst F. W. Alexanderson to any search. Noted and filed, but I think I'm beginning to be "overwhelmed by insurmountable opportunities". grin! --snip-- ( the Mohican antenna circuitry) Of the five bands (A-E, SW3 positions 5-1), the only one which seems different is "E", with an additional 130pF cap between the antenna and the tank circuit. Is that what you're referring to? I am merely pointing out the obvious application of a tapped inductor of the tuned front end serving as impedance match to an high-Z antenna (the topic of your choice). Oh. Okay. "Parallel LC (tank) circuit = high impedance. Coil tapped to match lower impedance". Gotcha. I got lost trying to figure out your reference to "conventional bands". ... The schematic abounds in examples. Yup. You don't see many AM/FM radios these days with three tank circuits per band. grin! ... One need only substitute values to serve the right frequency band - a simple exercise in reverse engineering employed since Hertz drew a spark across a gap at the base of a loop. Which was, in its own time, pretty close to "magic". I've been trying to stir some excitement in the one niece and nephew who are talking of studying engineering next year, but it's tough. They seem to be so constantly surrounded by wonders that they take them for granted. --snip-- ... Your learning lesson of maintaining the chassis ground with the trace is classic too. The discovery of corrosion brings up the common practice of taking ALL the tubes out and putting them back in to solve problems. It's still surprising to me just how often taking something apart and putting it together again will get it working again. Doesn't even require mystical passes with my hands (but I occasionally add them anyway grin!). ... Tightening ALL screws is another hard learned lesson that bench techs either get or don't get. Finished with the Mohican this afternoon. I wound up taking out the eleven machine screws around the IF/audio PC board out (they were all still tight, FYI). I then ran some fine steel wool around in the gap and reassembled it; turned out that I had to unbolt the audio transformer and 1/4" earphone jack to get the lockwashers and nuts back on four of them. When I finished there was no leftover hardware, a small miracle in itself. It still doesn't buzz. (Yayyyyy!) You probably could have got away with cheaper transistors by also substituting the bias diodes (56-7s) - but as events bore out, the transistors were good. If you note the difference between the base and emitter voltages, there is only about a tenth volt there. If I am to presume the diode call-out is for an 1N56, it is germanium too. Oh. A 56-7 is a 1N56? I wasn't sure about substituting them, and finding any Germanium parts on this side of the Pond is tough. I was about ready to bypass the entire audio section and wire in a small LM386-or-similar amplifier in its place. Might still do it next time. What is more amazing is this wasn't about the decrepitude of the electrolytic capacitors which usually suffer with time if they are not used for a long while. When I first heard the buzz, my first instinct was to check the electrolytics. I even tried parallelling the X7 emitter bypass, but because _that_ time I did it by hooking my jumpers to the component leads on top of the PC board, the effort had no effect. Ack! Phlbbbbt! So _close_... I have to say that those Gyrator circuits are really appealing. I may throw one togehter just to see what happens. Thanks for pointing me at them. (Now if someone would just design a "network component" that replaced _intelligence_ with four components, none of them involving intelligence... grin!) Thanks again for your feedback. Frank -- Fashion is...a search for a new language to discredit the old, a way in which each generation can repudiate its immediate predecessor and distinguish itself from it. -- Fernand Braudel/Civilization & Capitalism, 15th-18th Century -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) |
Designing an antenna for the 5000m band
On Feb 17, 11:05*pm, "Sal M. Onella"
wrote: "Phil Allison" wrote in message ... "Frnak McKenney" *http://ts.nist.gov/MeasurementServic...d/SP250-67.pdf ** Just how big is this file * * - *eh *?? Why did you limit replies to *ONE *newsgroup while posting *to TWO * ??? What sort to total *****ING *ASSHOLE *are you * ???? You ****ing *ASININE *YANK *****- head. ..... * Phil Uh-oh! *Looks like somebody isn't getting enough fiber! I think he just has "Little P***** Syndrome". So Sorry Phil for the little D***!!!! HI HI Joe |
Designing an antenna for the 5000m band
Frnak McKenney wrote:
In my current state of ignorance of the subject, this sentence has the appearance of a Zen koan: something that sounds non-sensical at first glance, but which, after sufficient time and effort studying, will undoubtedly become so blindingly obvious as to appear trivial. Thank you... I think. grin! As witnessed by the great Zen master, Yogi Berra...... Sorry, catching up on the groups and couldn't resist. - 73 de Mike N3LI - |
Designing an antenna for the 5000m band
On Feb 22, 9:19*pm, Frnak McKenney
wrote: On Sat, 21 Feb 2009 22:13:47 -0800, Richard Clark wrote: On Sat, 21 Feb 2009 19:37:34 -0600, Frnak McKenney wrote: --snip-- Google led me to the AAVSO site (www.aavso.org) which led me to the Yahoo VLF_Group. *Aaaaaaaaaaaaaaauuuuuuuggggh! *A circuit that can replace capacitors or inductors? *My first reaction is "technology at a level indistunguisable from black magic". I don't think I'm in Kansas any more. Gyrators have been around for a very long time, and can be found in a billion telephones, one probably within reach of you at the moment. They use telephones in Kansas don't they, Toto? *You can build one with four components (none of them an inductor) to make an inductor That's what the man said... I saw the schematics for Gyrators I-III, and I need to go back and re-read the decriptive text. more precisely than you could winding one. That doesn't take much. *I've had days recently where I felt like I could wind a mile of wire around a ferrite rod and _still_ not make an inductor. grin! If you truly want to be overwhelmed with the dark arts, try googling for "magnetic amplifiers." (Art would go ballistic knowing such a topic was in practice looooong before he left second form.) *No tubes, no transistors, and the orginal "solid state" design. *As this may sound as if it wanders from the subject of RF, add the name Ernst F. W. Alexanderson to any search. Noted and filed, but I think I'm beginning to be "overwhelmed by insurmountable opportunities". *grin! --snip-- ( the Mohican antenna circuitry) Of the five bands (A-E, SW3 positions 5-1), the only one which seems different is "E", with an additional 130pF cap between the antenna and the tank circuit. Is that what you're referring to? I am merely pointing out the obvious application of a tapped inductor of the tuned front end serving as impedance match to an high-Z antenna (the topic of your choice). Oh. Okay. "Parallel LC (tank) circuit = high impedance. Coil tapped to match lower impedance". Gotcha. I got lost trying to figure out your reference to "conventional bands". ... *The schematic abounds in examples. Yup. You don't see many AM/FM radios these days with three tank circuits per band. grin! ... *One need only substitute values to serve the right frequency band - a simple exercise in reverse engineering employed since Hertz drew a spark across a gap at the base of a loop. Which was, in its own time, pretty close to "magic". I've been trying to stir some excitement in the one niece and nephew who are talking of studying engineering next year, but it's tough. They seem to be so constantly surrounded by wonders that they take them for granted. --snip-- ... *Your learning lesson of maintaining the chassis ground with the trace is classic too. *The discovery of corrosion brings up the common practice of taking ALL the tubes out and putting them back in to solve problems. It's still surprising to me just how often taking something apart and putting it together again will get it working again. *Doesn't even require mystical passes with my hands (but I occasionally add them anyway grin!). ... *Tightening ALL screws is another hard learned lesson that bench techs either get or don't get. Finished with the Mohican this afternoon. *I wound up taking out the eleven machine screws around the IF/audio PC board out (they were all still tight, FYI). *I then ran some fine steel wool around in the gap and reassembled it; turned out that I had to unbolt the audio transformer and 1/4" earphone jack to get the lockwashers and nuts back on four of them. *When I finished there was no leftover hardware, a small miracle in itself. It still doesn't buzz. (Yayyyyy!) You probably could have got away with cheaper transistors by also substituting the bias diodes (56-7s) - but as events bore out, the transistors were good. *If you note the difference between the base and emitter voltages, there is only about a tenth volt there. *If I am to presume the diode call-out is for an 1N56, it is germanium too. Oh. *A 56-7 is a 1N56? *I wasn't sure about substituting them, and finding any Germanium parts on this side of the Pond is tough. I was about ready to bypass the entire audio section and wire in a small LM386-or-similar amplifier in its place. *Might still do it next time. What is more amazing is this wasn't about the decrepitude of the electrolytic capacitors which usually suffer with time if they are not used for a long while. When I first heard the buzz, my first instinct was to check the electrolytics. *I even tried parallelling the X7 emitter bypass, but because _that_ time I did it by hooking my jumpers to the component leads on top of the PC board, the effort had no effect. Ack! Phlbbbbt! So _close_... I have to say that those Gyrator circuits are really appealing. *I may throw one togehter just to see what happens. *Thanks for pointing me at them. *(Now if someone would just design a "network component" that replaced _intelligence_ with four components, none of them involving intelligence... *grin!) Thanks again for your feedback. Frank -- * * Fashion is...a search for a new language to discredit the old, * * a way in which each generation can repudiate its immediate * * predecessor and distinguish itself from it. * * -- Fernand Braudel/Civilization & Capitalism, 15th-18th Century -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all) One of the most common places gyrators are used today is in graphic equalizers. I wonder if a graphic equalizer could be built to cover the VLF band complete with LED bargraph(grim). The first graphic eq I ever saw had tons of coils in it and vaccums tubes and must have cost a few $K. The second one I saw was made with ICs no coils and cost about $500. It was replacing the first one I saw. JImmie |
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