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Author Topic: Satellite TV boxes -> Radio Telescopes?  (Read 1334 times)
AB1JX
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Posts: 15




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« on: October 17, 2012, 09:56:19 PM »

About the only things I've got that will receive 1 GHz and up are some old satellite TV boxes I got from the dump.  I don't care anything about watching TV on them, I'd like access to the frequencies they can tune, just for receiving. Getting a pair of them locked onto some frequency as an interferometer would be the ultimate goal.  Actually that might not be so impossible: if I remember right NTSC video is AM modulation so if you use the box to downconvert to TV channel 3 or 4 (common RF modulator output) you could pick signals out of the video passband (about 4.5 MHz wide I think).

But it's in the world of proprietary surface mount chips and unreadable eproms.  Anybody doing anything with turning some of this trash into useful receivers?  You could maybe almost run Linux on some of them instead of sending them to landfills.  Certainly they could be reprogrammed: they're made to accept firmware upgrades.  I've got an RCA/DirecTV DRD420, A Samsung SIR300W, a Dish/Echostar DP301 and a couple others.

There's a site on using some of the newer ones at http://lea.hamradio.si/~s57uuu/astro/sidi1/index.htm but all my stuff is older than that.

  Alan, ab1jx
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K0JEG
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Posts: 638




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« Reply #1 on: October 21, 2012, 10:13:23 AM »

Any satellite receiver since the 1980s would be looking for the LNB output frequencies of 950-1450MHz (assuming it was used for C band). Analog satellite video was actually frequency modulated, not vestigial sideband. Digital satellite video uses several different modulation schemes, QAM, QPSK or something similar. Note that the output of the LNB is inverted.

I don't know much about Ka and Ku receivers, but they are similar in that they look at downconverted frequency bands, and almost exclusively use digital modulation. Re-reading your post, they are all direct broadcast satellite (DBS) systems, on Ku band using digital modulation. You might be able to get something out but not really worth the trouble.

looking at this page: http://www.setileague.org/articles/protectd.htm it looks like modifying an LNB would be a better use of your time. But it might be even better to look at receiving 1420.406 MHz and looking for Hydrogen just to see what you get.
« Last Edit: October 21, 2012, 10:22:56 AM by K0JEG » Logged
AB1JX
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Posts: 15




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« Reply #2 on: October 21, 2012, 08:00:05 PM »

Which brings up another question: Aren't the LNBs they use just LNAs?  They don't actually try to downconvert with oscillators running out there in temperature extremes do they?  I assume the downconversion happens indoors and what's outside is just an amplifier.

I know people reload eproms for things like the Kindle Fire to run Linux on them, I thought maybe some people had set some of these up for general purpose use.  I suppose the only incentive would be for stealing TV, and you'd be hard-pressed to pay me to watch most of it.

http://www.mrao.cam.ac.uk/surveys/8C/8C.gif Is just a neat picture of a 38 MHz Yagi (one of 50) used as part of a radiotelescope in the UK in the 80s.  That's a road it's sort of straddling.
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K2OWK
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Posts: 1041




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« Reply #3 on: October 21, 2012, 10:13:11 PM »

Hello AB1JX, The answer is no. "LNA" stands for low noise amplifier. "LNB" stands for low noise block. They are not the same, and are not interchangeable.

73s

K2OWK
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MDNITERDER
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Posts: 146




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« Reply #4 on: October 26, 2012, 01:04:49 PM »

 I have heard of people using the older sat systems for SETI but thats about it.
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