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[Discuss-gnuradio] Radio astronomy data

From: Marcus Leech
Subject: [Discuss-gnuradio] Radio astronomy data
Date: Tue, 13 Mar 2007 00:04:00 -0400
User-agent: Thunderbird (X11/20070221)

I'm probably one of the few people on this list who cares, but here's an interesting plot of total power data taken at declination -29degrees, across 22 hours of right ascension. The chart shows data for three days, and an average over those three days. The main response is due to Sgr A--a source thought to be powered by the black hole at the center of the galaxy. The smaller hump at around 07:50 or so is the galactic plane in the region of
 the constellation Puppis.


The three days diverge somewhat here and there--due almost entirely to differences in diurnal heating/cooling cycles of the LNAs at the feed. I'm going to be adding temperature compensation in the receiver code that will allow me to tweak the effective gain, based on the current ambient temperature of the LNAs. I'll do that entirely numerically, since tweaking the hardware gain won't provide anywhere near fine-enough control. GaAsFET LNAs change gain with temperature, but only to the tune of a small fraction of a dB/C.

I'll "outsource" the thermal-probe interface to an outboard process, and plug it into the gr-radio-astronomy receiver through a named pipe that I'll read during my 1-second timer code.

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