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
Bruce,
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: http://pulsar.princeton.edu/%7Ejoe/K1JT/
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. http://radiosky.com/
73's, Ed - KL7UW ========================================= BP40iq, Nikiski, AK http://www.qsl.net/al7eb Amsat #3212 Modes: V - U - L - S USA Rep. for Dubus Magazine: dubususa@hotmail.com =========================================