-----Original Message-----
From: Vic Rosenthal <rakefet@rakefet.com>
To: Steve Thompson <g8gsq@qsl.net>; Amps reflector <amps@contesting.com>
To: <amps@contesting.com>
Date: 11 March 2002 15:46
Subject: Re: [Amps] Antenna vs. amp (was: al-1200 question)
>Steve Thompson wrote:
>>
>> On a 144MHz contest
>> station, set up on a site with sea takeoff from E to SW, swapping 2x9
yagi
>> for a 50R resistor does not change the noise we hear,
>
>This implies that what Tom called the average gain of the antenna is not
great
>enough to override the rx generated noise. A low-noise preamp would boost
both
>signal and noise from the antenna and solve this problem.
Rx noise figure measured 1.5-1.8dB.
>
>> swapping 50R for 4x19
>> yagi results in a clear increase in noise, I estimate about 3dB.
>
>This antenna has more gain, so you are now hearing atmospheric noise, as
you
>should.
I wouldn't expect the average gain, integrated over a sphere to be higher
than the 2x9. If anything, there's more potential sources of loss.
>
>> The earlier reasoning implies that we should get the same noise from both
>> antennas, but we don't. What are we hearing?
>
>In my earlier comment, I assumed (and didn't say!) that there was enough
output
>from the antenna to override internal rx noise.
I think there should have been, given the typical figures in noise
temperature charts.
73, Steve [Still puzzled, now with a headache :-) ]
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