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.
