[amsat-bb] Re: Pre amp question

Edward R. Cole al7eb at acsalaska.net
Fri Dec 15 07:42:48 PST 2006

At 10:47 AM 12/15/2006 -0400, you wrote:

>Thanks, Dom. This is excellent helpful advice for those of us with
>elevation rotors. The V2/V1 ratio with preamp on would provide a relative
>benchmark to turn to when something seems 'not quite right'. For instance,
>I know that ice buildup on my yagis due to freezing rain will degrade their
>performance. I could get some idea of how badly the performance degrades by
>comparing this 
>ratio in icy conditions to the benchmark taken in ideal conditions. (This
>would assume that the S component of the S+N was constant over time.
>Assuming I'm using ground noise, does anyone know if this value changes
>significantly with ground temperature? Transmitter phase noise as discussed
>above would, of course, be beyond one's control.) 
>I'm wondering if anyone knows of a reliable piece of software that might do
>the voltage measurements through a computer and sound card. I've noticed
>recent projects in QST that appear to entail this sort of measurement, but
>I don't think any of them had software that performed this basic function.
>73, Bruce VE9QRP


For antenna noise temperatures we use the kelvin scale 273K = 0C, so avg
temps of 17C (290K) will not significantly change for a few degrees change
(i.e. it is now -15C here = 5F, but this is 258K an change of 258/290).

If you want absolute accuracy then use your ambient temp in your calculations.

For sw that uses your soundcard, there are two I can recommend:  JT65 that
is used mainly for eme has a Moon Echo routine that one could use for
measuring hot/cold sky noise.  Free from:

SkyPipe is a free radioastronomy program that will display and graph noise
levels on a scale that would eliminate needing to use an audio meter.

Ed - KL7UW 
BP40iq,  Nikiski, AK      http://www.qsl.net/al7eb
Amsat #3212
Modes: V - U - L - S
USA Rep. for Dubus Magazine: dubususa at hotmail.com

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