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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) |
#2
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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 |
#3
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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 |
#4
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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) |
#5
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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 |
#6
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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 |
#7
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Designing an antenna for the 5000m band
Hey, his name is Frnak, doesn't he have enough troubles already?
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#8
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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 |
#9
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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 |
#10
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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 |
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