[hpsdr] Janus for Radio Astronomy

[Phil Harman]

Most interesting exchange.  One of our group is working on a bandscope that 
will display up to 55MHz of spectrum. Hope to have it working shortly.

73's Phil... VK6APH


----- Original Message ----- 
From: "hartfuss" <hartfuss at ipp.mpg.de>
To: "Barney Linet" <blinet8 at gmail.com>
Cc: <hpsdr at hpsdr.org>
Sent: Thursday, February 05, 2009 5:05 PM
Subject: Re: [hpsdr] Janus for Radio Astronomy


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