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[Discuss-gnuradio] DBS_RX/USRP warmup stability

From: Marcus Leech
Subject: [Discuss-gnuradio] DBS_RX/USRP warmup stability
Date: Mon, 09 Jan 2006 17:27:23 -0500
User-agent: Mozilla Thunderbird 1.0 (X11/20041206)

One of the things that's quite important to RA types is the stability of the receiving equipment over longish time periods--particularly over periods that are the same order of magnitude as the signals they're
 trying to observe.

I happened to have shut down my USRP/DBS_RX stack today to do some enclosure upgrades, so it had cooled down to room temperature (20C). Once I brought it back up, I noticed the baseline drift upwards over a period of 20 minutes, and then it stabilized. It drifted 0.275dB in those 20 minutes, and after reaching operating temperature, seems to be stable to roughly 0.025-0.05dB, with random excursions occurring over
 periods of a few minutes.

Something that's interesting is that the system can detect when I'm sitting at the computer, but not necessarily typing anything. Since my feedhorn is pointed out the window, it must be seeing a reflection of my blackbody radiation. I confirmed that my feedhorn was able to see me, by placing my hand in front of the feed--sure enough a significant rise in the detected baseline resulted. That means that the front-end LNA and feedhorn is working properly in that they're able to see my
 blackbody radiation. Humans make good weak-signal microwave sources :-)

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