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Horizontal loop antenna



 
 
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  #21  
Old February 20th 08, 04:22 AM posted to rec.radio.amateur.antenna
Cecil Moore[_2_]
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Posts: 3,522
Default Horizontal loop antenna

Dave Platt wrote:
On the other hand, page 16 of the SGC-230 manual PDF specifically
shows a balanced dipole, being fed through "balanced line feeders,
300-600 ohms, up to 40 feet".


My 1990 manual shows nothing like that. Maybe they changed
their minds about balanced line feeders.
--
73, Cecil http://www.w5dxp.com
  #22  
Old February 20th 08, 05:43 AM posted to rec.radio.amateur.antenna
Dave Platt
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Posts: 464
Default Horizontal loop antenna

On the other hand, page 16 of the SGC-230 manual PDF specifically
shows a balanced dipole, being fed through "balanced line feeders,
300-600 ohms, up to 40 feet".


My 1990 manual shows nothing like that. Maybe they changed
their minds about balanced line feeders.


Could be... I was using a PDF copy of the manual I downloaded from the
SGC website. Possibly the newer versions of their couplers have more
flexibility in their tuning algorithm?

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
  #23  
Old February 20th 08, 06:44 AM posted to rec.radio.amateur.antenna
Richard Clark
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Posts: 2,951
Default Horizontal loop antenna - Dual Wire

On Tue, 19 Feb 2008 22:55:20 -0500, Buck
wrote:

I seem to remember an article about someone taking a full-wave
horizontal loop antenna and making two loops (or was it a half-wave
loop?). The second loop caused the antenna to match 50 ohms so it
could be fed with coax and (I think) it operated multiple bands.
Anyone remember this article and know where it might be?


Hi Buck,

It is a small tuned loop (less than a tenth wave) with a smaller loop
(about a third to a fifth in size of the first loop) inside it.

Not much else to say except that polarity is vertical/horizontal when
the loops are in the horizontal/vertical plane. Make every effort to
build low Ohmic connections and elements. The capacitor will have to
stand off a high voltage (and many caps suffer from ESR).

73's
Richard Clark, KB7QHC
  #24  
Old February 20th 08, 08:40 AM posted to rec.radio.amateur.antenna
Richard Harrison
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Posts: 588
Default Horizontal loop antenna

Roy Lewallen wrote:
"I don`t see anywhere in the response which explains how "radiation is a
function of loop area" and why increasing the loop circumference would
be advantageous."

Didn`t want to bore with details. Terman knows all and tells all. His
loop antenna story begins on page 907 of his 1955 opus:
"The radiation resistance of a loop antenna is less the smaller the loop
area. For the radiation resistance to be large enough to give good
antenna efficiency, it is necessary that the loop perimeter be of the
order of a wavelength. This introduces a difficulty, since when the
perimeter approaches or exceeds a half wavelength, then the loop current
in Fig. 23-40 will not be constant, nor will its phase nnecessarily be
the same in different parts of the loop. The prectical solution is to
build up the loop in such a way that the perimeter consists of resonant
antennas so arranged that the current everywhere in the loop perimeter
flows in the same direction around the loop. A variety of practical
physical arrangements for achieving this result have been devised, three
examples of which are illustrated in Fig. 23-41."

Yet another elegant phase inverter from Kraus as applied to a colinear
dipole appears on Cecil`s webpages.

Best regards, Richard Harrison, KB5WZI

  #25  
Old February 20th 08, 09:40 AM posted to rec.radio.amateur.antenna
Richard Harrison
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Posts: 588
Default Horizontal loop antenna

Roy Lewallen wrote:
"Perhaps you build antennas for radiation resistance, but I think most
people build them to maximize radiation in some particular direction.."

You must have some radiation resistance or you have no signal, but not
all antennas are highly directional.

Page 8-10 of the 20th edition of the ARRL Antenna Book has (Eq 5):
Efficiency = radiation resistance / radiation resistance + loss
resistance

Zero radiation resistance = zero efficiency.

Best regards, Richard Hsarrison, KB5WZI

  #26  
Old February 20th 08, 12:00 PM posted to rec.radio.amateur.antenna
Buck[_2_]
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Posts: 118
Default Horizontal loop antenna - Dual Wire

On Tue, 19 Feb 2008 22:44:48 -0800, Richard Clark
wrote:

On Tue, 19 Feb 2008 22:55:20 -0500, Buck
wrote:

I seem to remember an article about someone taking a full-wave
horizontal loop antenna and making two loops (or was it a half-wave
loop?). The second loop caused the antenna to match 50 ohms so it
could be fed with coax and (I think) it operated multiple bands.
Anyone remember this article and know where it might be?


Hi Buck,

It is a small tuned loop (less than a tenth wave) with a smaller loop
(about a third to a fifth in size of the first loop) inside it.

Not much else to say except that polarity is vertical/horizontal when
the loops are in the horizontal/vertical plane. Make every effort to
build low Ohmic connections and elements. The capacitor will have to
stand off a high voltage (and many caps suffer from ESR).

73's
Richard Clark, KB7QHC


The antenna article I was referring to is either full size or 1/2 size
horizontal loop and he used window line (twin-lead) wire for the loop
crossing the connection of the coax so that the wire made a continuous
loop twice going from the center conductor to the shield (he may have
used a balun, but you get the idea). This was a large loop running
around his yard.

Thanks, tho.

Buck
N4PGW
--
73 for now
Buck, N4PGW

www.lumpuckeroo.com

"Small - broadband - efficient: pick any two."
  #27  
Old February 20th 08, 01:02 PM posted to rec.radio.amateur.antenna
LA4RT Jon Kåre Hellan
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Posts: 16
Default Horizontal loop antenna

(Richard Harrison) writes:

Roy Lewallen wrote:
"Perhaps you build antennas for radiation resistance, but I think most
people build them to maximize radiation in some particular direction.."

You must have some radiation resistance or you have no signal, but not
all antennas are highly directional.

Page 8-10 of the 20th edition of the ARRL Antenna Book has (Eq 5):
Efficiency = radiation resistance / radiation resistance + loss
resistance

Zero radiation resistance = zero efficiency.

Best regards, Richard Hsarrison, KB5WZI


You're right that low radiation resistance makes it hard to attain
high efficiency. You want radiation resistance to be significantly higher
than loss resistance.

But ohmic losses usually aren't that bad in large dipoles and
loops. EZNEC or other modeling progarms can tell you how much you gain
by going up in wire size. For common geometries and wire sizes, the
difference will be a small fraction of a decibel.

For small ("magnetic") loops on the other hand, efficiency is very
much an issue, and you want to push the radiation resistance as high
as you can, and ohmic losses as low as you can. (Increasing the size
of the loop is the easiest way to increase radiation resistance, but
presumably there's a reason that you'er using a small loop in the
first place.

73
LA4RT Jon, Trondheim, Norway
  #28  
Old February 20th 08, 03:46 PM posted to rec.radio.amateur.antenna
Richard Harrison
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Posts: 588
Default Horizontal loop antenna

Jon, LA4RT wrote:
"---but presumably there`s a reason that you`re using a small loop in
the first place."

True. In Norway I specified large dishes for scatter communications with
North Sea platforms but the government sponsored the geosynchronous
satellite program and ignored scatter. In the many tunnels I specified
300-ohm twinlead which works about as well as Andrew`s leaky coax and
costs much less. I think Norway is too rich to care about cost.

Best regards, Richard Harrison, KB5WZI

 




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