[hpsdr] Janus for Radio Astronomy

[hartfuss]

Barney, that's very interesting. I would be pleased to see a block 
diagram of the whole set-up and to get information about the antenne you 
are using.
To measure the 21 cm-line is still on my program for the next years. I 
also thought to use PowerSDR and it's nice features, however, then also 
realized the problem with the somewhat too small bandwidth you mentioned.
To see the full Doppler-shift when looking into the arms of the galaxy, 
the bandwidth should be at least 1.5 MHz. Not long ago somebody 
mentioned her in the reflector that and how (FPGA programming) this 
should easily be possible with Mercury.
A few years ago I already build a down-converter 1420 to 145 MHz with 
two different LOs to apply frequency hopping and lock-in difference 
technique to recover the spectral information (line shape) with 
sufficient S/R, which works. The line then should be scanned by sweeping 
the frequency of the  2m-receiver.
It has, due to other activities, not been completly finished so far.
It would be nice to stay in contact.
Best 73s, Hans , DL2MDQ.


Barney Linet schrieb:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> 
> 
> ------------------------------------------------------------------------
> 
> 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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