The first time I made an experience with radio astronomy at a very low level was back in 1979, when I turned my 2m dish for tropo to the sun during sunset. I measured the audio output of my receiver with a millivoltmeter, and observed a 2 dB increase of noise on 23cm. That was before I started with EME.
A few years later I built a 5m dish for EME, and from this time onwards I did regular sun noise measurements on 70cm and 23cm to check the system performance.
With my next dish growing to a size of 10m diameter it was even possible to measure moon noise. Sun noise is unstable and low on 2m, this was the reason I started to measure radio galaxies as well. Cygnus, Sagittarius and Taurus were all easy to detect with a 10m dish on 2m, 70cm and even on 23cm. The millivoltmeter was replaced by an Af rectifier, ADC and a PC program to read, plot and store data.
Levels down to a few tenth of a dB can be measured using the 2.5 kHz SSB bandwith of a normal station receiver. But you need low pass filtering with a time constant up to a minute in that case to achieve a smooth curve. Therefore measuring quick changes in signal level is impossible. For pulsar measurements for example the time constant can only be a few milliseconds maximum.
The only way to measure differences of milli-dB is to increase bandwidth. You can see the advantage of a large bandwidth by looking at the drift scan measurements of moon noise I did with 2.5kHz bandwidth and with 2MHz bandwidth.
moon noise at 7,3m offset dish recorded with 2,5 kHz bandwidth
moon noise at 7,3m offset dish recorded with 2 MHz bandwidth
There are several subjects in radio astronomy.
Recently I concentrated on detecting pulsars.
A few years ago I made some nice plots of Cygnus A
Measuring HI line is not so difficult (compared to pulsars!) but also interesting.
The Sun Eclipse measurements back in 1999 were a 'once in a lifetime' chance!
See the links below.......
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