Thanx all!

"Richard Harrison" wrote in message
...
Bob Miller was quoting the originaql questioner.

Bob recommended "Better Shortwave Reception" by William Orr.

Orderd from alibris.com for ~$6.00! Also orderd the ARRL handbook for ~$30
used!

Good advice, and the "Radio Handbook" recently published by Howard Sams
and edited by William Orr is a good source of elementary theory too.

Best regards, Richard Harrison, KB5WZI

Is this an explanation of the term 'capture area' I hear a lot of hams
use.

regards, Jer

As a 'rule of thumb' the captured signal power in small loops is
proportional to the area enclosed by the loop. Twice the area = twice
the
power (3 dB).

The typical dimensions given for these loops allow them to be used on
either
160M or 80M -- and as you have surmised, the loop can be larger for 160M
only.

73, Gary
K9AY
_________

Subject: [Antennaware] Shielded loop receive antennas.


In the ARRL antenna handbook (and repeated elsewhere) is a design for
a 160m shielded rx loop antenna with 5ft square sides.

Can anyone advise me how the strength of the recovered signal would
change if the loop was made bigger. By using low-capacity coax I
think I could still resonate a loop that has 7ft square sides. This
would very nearly double the **AREA** of the loop, I would like to
understand how this would affect the received signal.

Any thoughts would be appreciated.

73,

Here is a site for examples of capture areas of antennas

http://www.sommerantennas.com/gain.html

--
CL -- I doubt, therefore I might be !


"k" wrote in message
...
Is this an explanation of the term 'capture area' I hear a lot of hams
use.

regards, Jer

As a 'rule of thumb' the captured signal power in small loops is
proportional to the area enclosed by the loop. Twice the area = twice
the
power (3 dB).

The typical dimensions given for these loops allow them to be used on
either
160M or 80M -- and as you have surmised, the loop can be larger for 160M
only.

73, Gary
K9AY
_________

Subject: [Antennaware] Shielded loop receive antennas.


In the ARRL antenna handbook (and repeated elsewhere) is a design for
a 160m shielded rx loop antenna with 5ft square sides.

Can anyone advise me how the strength of the recovered signal would
change if the loop was made bigger. By using low-capacity coax I
think I could still resonate a loop that has 7ft square sides. This
would very nearly double the **AREA** of the loop, I would like to
understand how this would affect the received signal.

Any thoughts would be appreciated.

73,

Caveat Lector wrote:
Here is a site for examples of capture areas of antennas

http://www.sommerantennas.com/gain.html

--
CL -- I doubt, therefore I might be !

As a 'rule of thumb' the captured signal power in small loops is
proportional to the area enclosed by the loop. Twice the area = twice
the
power (3 dB).


That's all nonsense, including the Sommer site!!

Capture area, more correctly called effective aperture, and gain has
nothing directly to do with physical area of an antenna. It is strictly
a function of the operating wavelength and gain of the antenna.

If I double the size of an antenna the capture area (effective
aperture) might increase, decrease, or stay the same.

If I have a small loop and it has zero loss, the capure area is
effectively very large.

If I have a full size dipole and add enough loss resistance, capture
area is very small.

Capture area is generally an excuse people make to justify using a
larger antenna, even if the antenna does not work as nearly as well.
"My quad works great for receiving because it has large capture area."
Nonsense. If it has the same gain as a Yagi on the same band, it has
exactly the same capture area. If it has less gain than a Yagi (which
many quads do, hence the reason you don't see them in contest stations)
it has less capture area.

I'd be ashamed if I was selling antennas and did not understand what
capture area was.

73 Tom

You can also find many postings explaining capture area by doing a
groups.google.com search of this newsgroup for the phrase "capture
area". I've explained it here several times.

Roy Lewallen, W7EL

Caveat Lector wrote:
Here is a site for examples of capture areas of antennas

http://www.sommerantennas.com/gain.html

Caveat Lector wrote:
Here is a site for examples of capture areas of antennas

http://www.sommerantennas.com/gain.html


Have you got a link to a similar site that covers ferrite rod antennas?

On Fri, 24 Mar 2006 06:57:21 -0800, "Caveat Lector"
wrote:

Here is a site for examples of capture areas of antennas

http://www.sommerantennas.com/gain.html


Are you recommending it?

Is the following statement from the page correct?

"Note: Antenna B has only half the capture area of antenna A and is
therefore able to "catch" only 50 percent of the electromagnetic
field; e.g., 50mV, compared to 100 mV/50 Ohms. This means 6dB less
gain for antenna B in comparison to antenna A."
--

Caveat Lector wrote:
Here is a site for examples of capture areas of antennas

http://www.sommerantennas.com/gain.html

John Popelish wrote:
Have you got a link to a similar site that covers ferrite rod antennas?

I hope this question isn't taken the wrong way, but why would you want
a similar site? That one is terrible for accuracy. The poor fellow who
wrote that page doesn't even know what capture area is.

Wouldn't it be better to find a totally different type of site, one
that at least has some technical accuracy?

73 Tom

wrote:
Caveat Lector wrote:

Here is a site for examples of capture areas of antennas

http://www.sommerantennas.com/gain.html


John Popelish wrote:
Have you got a link to a similar site that covers ferrite rod antennas?


I hope this question isn't taken the wrong way, but why would you want
a similar site? That one is terrible for accuracy. The poor fellow who
wrote that page doesn't even know what capture area is.

I meant a site that addressed (correctly, one would hope) that concept
of capture area for rod antennas.

Wouldn't it be better to find a totally different type of site, one
that at least has some technical accuracy?

Okay, I'll take one of those. :-)

What information are you looking for, capture area or effective height?
Capture area determines how many watts you'll get into a conjugately
matched load connected to the antenna. Effective height determines how
many volts you'll get from an open circuited antenna. The two aren't
directly related. For more information about the two topics, do a
groups.google.com search for postings I've made on those topics in this
newsgroup.

As I've posted here quite a number of times before, the capture area of
a lossless infinitesimally short dipole is very nearly as great as that
of a half wave dipole, in their most favored directions. (The difference
is about 10%, and it's due to the slight pattern shape difference caused
by different current distributions). So except for loss the capture area
of a ferrite rod antenna is within 10% of that of a dipole. But loss in
a ferrite rod antenna will reduce the capture area considerably. If
you're interested in knowing how much power you can get from a ferrite
rod, then, what you need to know is its efficiency, which is a function
of wire length, number of turns, and the antenna feedpoint impedance. I
don't have the time right now to work it out for you.

The effective height of a ferrite rod antenna is approximately:

(2 * pi * mueff * N * A) / lambda

where

mueff = effective relative permeability of the rod (mainly a function
of rod length)
N = number of turns
A = rod cross sectional area
lambda = wavelength

Roy Lewallen, W7EL

John Popelish wrote:
wrote:
Caveat Lector wrote:

Here is a site for examples of capture areas of antennas

http://www.sommerantennas.com/gain.html


John Popelish wrote:
Have you got a link to a similar site that covers ferrite rod antennas?


I hope this question isn't taken the wrong way, but why would you want
a similar site? That one is terrible for accuracy. The poor fellow who
wrote that page doesn't even know what capture area is.

I meant a site that addressed (correctly, one would hope) that concept
of capture area for rod antennas.

Wouldn't it be better to find a totally different type of site, one
that at least has some technical accuracy?

Okay, I'll take one of those. :-)