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Re: Re: Receiver performance



Doug,

Good info. I would be a little concerned that sun noise is not a constant
either. As I recall we were doing sun noise measurements on 70cm with a big
array and it varied considerably, even over the period of a few minutes. If
the sun is quiet, that's not much of a problem. Nevertheless, it is one more
tool in being able to evaluate our rx setups and I thank you for your info
and hope you post more of the same. 73


hasan schiers, NØAN
schiers@netins.net

----- Original Message -----
From: "Douglas Braun NA1DB" <doug@dougbraun.com>
To: <amsat-bb@AMSAT.Org>
Sent: Tuesday, May 29, 2001 11:48 AM
Subject: Fwd: Re: [amsat-bb] Receiver performance


> Hello,
>
> Below is a good tip for doing noise measurements.  The advantage
> of using CoolEdit on a captured sound sample is that you can
> get a power level reading averaged over as much time as you want,
> to reduce the random variation of the signal level.  I captured
> 30 seconds of sky and sun noise signal at a time, and the variation
> was something like 0.01 or 0.02 dB.  If you average only one
> second, there is about a 0.1 dB uncertainty.
>
> If you are a perfectionist, you could also use Cool Edit to
> filter your sound sample to a 300-2500 Hz bandwidth, to eliminate
> errors due to soundcard DC offset, AC hum, out-of-band audio
> noise, etc.
>
> With my 2-foot dish I see 1.0 dB of sun noise.  Ed Cole's g-t.xls
> spreadsheet says I should be getting at least 2dB.
> I think I will try making one of those cupped-reflector helix feeds,
> and seeing if it helps.
>
> Everybody should do the sun-noise test.
> It does not lie.  Estimating your system performance by measuring
> the AO-40 beacon strength is a much less accurate and repeatable
> technique, since it depends on the satellite's squint angle,
> transmitter output, etc.
>
> Doug
> NA1DB
>
> >CoolEdit will do RMS averaging. Check under Analyze | Statistics
> >
> >http:// www.syntrillium.com
> >
> >73,
> >Mike, N1JEZ
>
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>

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