Jim,
You are correct on the forward gain measurements but there is yet another
aspect to it.
But that's only half of the story.
A multi-element yagi will have a lower angle of radiation than a simple
dipole at the same height.
This lower angle of radiation can result in significantly stronger signals
at certain times of the day; much more than the 3 to 5dB the beam brings in
near-field measurements. Sometimes it's a couple of S-units.
In addition, the reduction of noise off of the back and sides often results
in a better signal to noise ratio; of course not if your beam is pointing in
the direction of the noise (hi).
73
Rick, Dj0IP
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Jim Brown
Sent: Tuesday, October 01, 2013 8:49 PM
To: tentec@contesting.com
Subject: Re: [TenTec] Value of RX Only Antennas
On 10/1/2013 7:51 AM, Richards wrote:
> These receive only antennas are nice to have, but I figure it is
> better to improve one's transmit antennas if possible - especially if
> one can can replace them with antennas with more gain.
RX-only antennas are most useful on bands where it is impractical or
expensive to get directivity from your TX antenna -- 160, 80, 60, 40, and
30.
Another VERY important point. Contrary to manufacturers' claims, it is VERY
difficult to get much more than about 5 dB gain over a dipole with a
collection of aluminum on a boom. That was the clear result of extensive
measurements by N0AX and K7LXC of a dozen or so of a broad selection of
tri-banders. An M-squared C3 was the best of the small ones, with an
average gain of 3.4 dB across the three bands. A Mosley
TA33 was only 1.6 dB (loss in the traps made the difference). An M-squared
C-31XR (31 ft boom) was the best of the big ones with 5.3 dB over a dipole,
a Cushcraft X9 was 5dB, a Bencher Skyhawk was 4.4 dB, the rest were less
than 4 dB, and several big Mosley antennas had negative gain!
73, Jim K9YC
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