[TowerTalk] Yagis and Receive Strength

[k6ll@juno.com]

On Fri, 23 Jul 1999 13:40:15 -0500 Richard Thorne <rthorne@tcac.net>
writes:
>
>Hi Guys:
>
>I've been working pretty hard on getting my transmitted signal
>improved.  I have stacked F12 C3's (45' and 75' which appears to be a
>good compromise distance) and a new Acom 2000A Amplifier was just
>installed.
>
>Well things are good and I feel like an alligator.  On 15 the other 
>day
>I had a good pileup going, but I couldn't hear most of the stations
>calling.  I'm not sure if thats due to the power and antenna types of
>those stations, or if I need to continue improvements on my end.
>
>So heres my ignorant question (kind of embarrassing too), does a 
>larger
>yagi, i.e. going from 2 elements to say 4 elements improve receiving 
>as
>well as transmitting?  While I'm only stacking 2 Force 12 C3's (which
>gives me 2 elements on each band times two) it seems to me that I'm
>improving my receive capability better than I would with a single
>antenna with 4 elements on each band.
>
>I would love to stack a pair of C31XR's but I would have to get a 40
>meter beam and I'm sure this exceed the limits of my 25g tower.
>
>Whats the multitude think?

The real limitation on receive is not absolute signal level,
but rather signal-to-noise ratio. That's why hardline always
helps on transmit, but RG-58 is usually just as good for hf
receiving.

SNR was discussed here a few months ago, and I think
the consensus was that, if noise is arriving equally from
all directions of azimuth and elevation, and if the desired signal
is in the main beam of the antenna, signal-to-noise ratio is
improved by an amount equal to the gain of the antenna. If both the
predominant noise source and the desired signal are in the main beam
of the antenna, there is little or no improvement. For man-made local
noise, with multiple azimuth sources, all near zero degrees elevation,
I would think that a single long yagi would have an advantage over a
short stack, since the azimuth beamwidth is narrower. If the long single
yagi were at the height of the top antenna in the stack, there would
be additional immunity to noise generated by one's immediate neighbors,
or in one's own household, due to the increased seperation distance in
the near field.

Regardless of all that, if you are running 1500 watts, there is a
significant layer of stations that you will never be able to hear, no
matter what you do, because some of the non-reciprocal factors are
not under your control.

Dave Hachadorian, K6LL
San Diego, CA
K6LL@juno.com

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