"John Popelish" wrote in message
...
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?

Try URL:

http://www.st-andrews.ac.uk/~jcgl/Sc...rt7/page5.html

Some others using Google
--
CL -- I doubt, therefore I might be !

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."
--

On Sat, 25 Mar 2006 01:09:06 GMT, Owen Duffy wrote:

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?

Unanswered...


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."

Of course it is not.

The article seems based on some typical misconceptions about Capture
Area and the suggestion that you can run a ruler over a dipole (loaded
or otherwise) to measure up and calculate the capture area is
nonsense.

I wonder if that is how Somner derive the gain figures that they
publish for their antennas. (Gain is related to Capture Area, and if
they don't understand Capture Area, do they understand Gain?)

Owen
--

(My information for this comes from a number of websites including
commercial antenna sites. Needless to say, the accuracy of any
information, especially that of commercial sites is suspect.)


I have been reading about reduced size antennas using capacity hats
instead of, or in addition to, inductor loading. Most sites claim
that capacity hats reduce size with much less (or no) signal loss
compared to a full size antenna. At least one site claims a vertical
1/4 dipole using cap-hats has gain over a 1/4 vertical ground plane.
The consensus seems to be that size for size, the antenna shortened by
capacity hats has less loss than the same size antenna shortened by
inductors as per http://www.sommerantennas.com/gain.html (taken from
another thread in this newsgroup.)

Some claims are that the capacity hat antennas have equal signal
strength to their full-sized counterparts.

My research, thus far, my theory is:

1) any shortened antenna will have some loss compared to its
full-sized counterpart. (i.e. an 80 meter dipole shortened by one
foot using capacity hats will not be as efficient as the full length
version, even though one might be hard pressed to find the instrument
that could measure it.)

2) antennas shortened with capacity hats have less loss than those
shortened by inductors

3) capacity hat antennas exhibit slightly more bandwidth than inductor
loaded antennas

4) given equal length, a cap-hat vertical dipole will exhibit equal,
(or according to some sites, greater) signal strength to a vertical
monopole either reduced or full-size.



Size Loss vs efficiency of a cap-hat dipole.

Assuming my first point of theory is correct, there must be a point in
which the reduced size of a dipole using only capacity hats is
noticeable. Continued reduction finds additional noticeable points of
loss.

What I would like to know is approximately where those points might be
so the 'value' of a cap-hat dipole antenna can be determined given
some acceptable size or loss.

An example might be I have 25 feet of antenna pole. I can build an
antenna with what I have. However, it may be that for ten more feet
of pole, I can have a much better signal. Should I use what I have,
or order the additional ten feet of aluminum?

Another example would be to estimate the maximum power I can run on 60
meters using a given length antenna. If a 1/4 wave dipole will
radiate almost as effectively as a 1/2 wave, then I would not worry
about adding the extra 5 or ten watts I would need to max the ERP out,
but if the loss were significant, I would know I can leave my radio on
full power (100 watts) without committing a violation.

Thank you for your thoughts.







--
73 for now
Buck
N4PGW

"Buck" wrote in message
...
(My information for this comes from a number of websites including
commercial antenna sites. Needless to say, the accuracy of any
information, especially that of commercial sites is suspect.)


I have been reading about reduced size antennas using capacity hats
instead of, or in addition to, inductor loading. Most sites claim
that capacity hats reduce size with much less (or no) signal loss
compared to a full size antenna. At least one site claims a
vertical
1/4 dipole using cap-hats has gain over a 1/4 vertical ground plane.
The consensus seems to be that size for size, the antenna shortened
by
capacity hats has less loss than the same size antenna shortened by
inductors as per http://www.sommerantennas.com/gain.html (taken from
another thread in this newsgroup.)

Some claims are that the capacity hat antennas have equal signal
strength to their full-sized counterparts.

My research, thus far, my theory is:

1) any shortened antenna will have some loss compared to its
full-sized counterpart. (i.e. an 80 meter dipole shortened by one
foot using capacity hats will not be as efficient as the full length
version, even though one might be hard pressed to find the
instrument
that could measure it.)

2) antennas shortened with capacity hats have less loss than those
shortened by inductors

3) capacity hat antennas exhibit slightly more bandwidth than
inductor
loaded antennas

4) given equal length, a cap-hat vertical dipole will exhibit equal,
(or according to some sites, greater) signal strength to a vertical
monopole either reduced or full-size.



Size Loss vs efficiency of a cap-hat dipole.

Assuming my first point of theory is correct, there must be a point
in
which the reduced size of a dipole using only capacity hats is
noticeable. Continued reduction finds additional noticeable points
of
loss.

What I would like to know is approximately where those points might
be
so the 'value' of a cap-hat dipole antenna can be determined given
some acceptable size or loss.

An example might be I have 25 feet of antenna pole. I can build an
antenna with what I have. However, it may be that for ten more feet
of pole, I can have a much better signal. Should I use what I have,
or order the additional ten feet of aluminum?

Another example would be to estimate the maximum power I can run on
60
meters using a given length antenna. If a 1/4 wave dipole will
radiate almost as effectively as a 1/2 wave, then I would not worry
about adding the extra 5 or ten watts I would need to max the ERP
out,
but if the loss were significant, I would know I can leave my radio
on
full power (100 watts) without committing a violation.

========================================
Buck,

For the same reduction in height a top hat has greater efficiency than
a loading coil. It can amount to 3 or more decibels.

But a top hat gets in the way and is more unsightly than a coil.

Have you seen program TOPHAT available from website below.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

The ARRL Radio Amateur's Handbook (ANY year) is a little less
intimidating than the Antenna Handbook. The Antenna Handbook is enough
for most of us for many years.

On Sun, 19 Mar 2006 02:23:07 GMT, "Lisa Simpson"
wrote:

Can anyone point me at a good book or website that can teach me about
antenna theory from a beginner's standpoint? I'm getting into SWL & feel I
really need to understand this subject well . . .

John Ferrell W8CCW

Lisa:
Check out the SWL oriented antenna links at URL:
http://ac6v.com/swl.htm#ANT

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



"Lisa Simpson" wrote in message
. ..
Can anyone point me at a good book or website that can teach me about
antenna theory from a beginner's standpoint? I'm getting into SWL & feel
I
really need to understand this subject well . . .

ORIGINAL MESSAGE:

Lisa Simpson wrote:

Can anyone point me at a good book or website that can teach me about
antenna theory from a beginner's standpoint? I'm getting into SWL &
feel I really need to understand this subject well . . .



*********** REPLY SEPARATOR ***********

The ARRL Antenna Handbook starts at the very beginning and goes as far
as you would like for ham radio designs. If you become so enthralled
with antennas that you want to go into it professionally, there are
other books but for us hams. that one will do.

Bill, W6WRT

On Sun, 19 Mar 2006 02:23:07 GMT, "Lisa Simpson"
wrote:

Can anyone point me at a good book or website that can teach me about
antenna theory from a beginner's standpoint? I'm getting into SWL & feel I
really need to understand this subject well . . .


Better Shortwave Reception, by William Orr, out of print, but a used
copy is at:

http://www.alibris.com/search/search...MDVKJzo0z0Tvng

Mr. Orr was one of the more understandable writers on things
electronic...

bob
k5qwg

Bob Miller wrote:
"Can anyone point me at a dood book or website that can teach me about
antenna theory from a beginner`s viewpoint?"

The ARRL 2006 Handbook devotes Chapter 22 to that task and provides a
good bibliography at the end of the chapter for further study.

Best regards, Richard Harrison, KB5WZI