[Amps] Antenna vs. amp (was: al-1200 question)

[WYsixK]

Steve,

Virtually every object emits background RF radiation that can be heard with a good antenna,
although I'd be a bit puzzled that you could hear it on a freq as low as 144 mhz with a single
yagi.  You can clearly hear this background radiation with a high gain eme antenna system.  Point
it at the sky and you hear a certain noise level.  Point it at the sun and you hear sun noise. 
Point it at a grove of trees 4 miles away and you can hear the trees.  An explanation that fits
your set of facts is that you were hearing sky noise and a higher gain antenna will certainly
incrase the level of sky noise that you hear.  It would be pretty constant on all azimuth
headings.  But a little experimentation - point at sun and terrestrial objects -  will prove or
disprove the hypothesis.

Michael

--- Steve Thompson <g8gsq@qsl.net> wrote:
> 
> -----Original Message-----
> From: Vic Rosenthal <rakefet@rakefet.com>
> To: Steve Thompson <g8gsq@qsl.net>; Amps reflector <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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