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)

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

"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

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)

"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

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

Hey, his name is Frnak, doesn't he have enough troubles already?

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

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

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