[Discuss-gnuradio] Radio astronomy data

[Marcus Leech]

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.

http://www.propulsionpolymers.com/radioastronomy/sgr_a_pavg20070312.png

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.