[hpsdr] Janus for Radio Astronomy

[Barney Linet]

As a project, I decided to make a receiver for detecting spectral line
radiation from neutral hydrogen in space. Clouds of cold, rarefied hydrogen
gas far out in space emit radio waves with a frequency of 1,420.406 Mhz.
this well known hydrogen line has been used for the past 60 years by radio
astronomers to map out the structure of the galaxy, gauge relative speeds of
different parts of the galaxy and so forth. first detected in the late 40's
or early 50's it is not easy to put your finger on. The old-time
radioastronomers used huge dish antennas to collect line radiation for
noisy, insensitive
vacuum tube behemoths.they relied on brute force detection (tune to a single
freq, collect energy and integrate.)

I used more modern components including cascaded LNAs and filters, a 1420 to
70 MHz image rejection mixer, more cascaded LNAs at 70 MHz, and a
Minicircuits 70 MHz I and Q demodulator. The baseband I and Q signals are
fed to Janus.

Power SDR includes a spectrum scope which I played with, until I had a
display that showed the spectrum around the magic frequency. At a sample
rate of 192 ksps, the bandwidth is a bit narrow for a neutral hydrogen
radio, this corresponds to a 40 km/sec velocity window. the doppler shifted
line radiation from clouds in the galaxy is more in the range anywhere from
plus-or-minus 250 km/sec. Never the less, nearby (relatively speaking)
clouds will have a limited range of speeds and stronger radiation. (Stuff
farther away is usually moving faster, in astronomy).

Well, to make a long story short, I did see features in long time average (4
sec ) FFT waterfall and spectrum. I dont know if these features are truly
hydrogen spectral line radiation, but I will continue to investigate.
Another use for an HPSDR! 73's de KC8LTD
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