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By jramurray - Posted on 03 September 2010

I wonder if anybody can help me with this question I am after an item from a satellite TV set up. The LNB at the dish is connected via a coaxial cable to a set-top box. What I am after is the RF unit in this set-top box. It is the bit with the F connector socket on it that the cable from the LNB plugs into. I need four of these if possible. These will not be used to repair any particular make of receiver. They are to be used in an amateur radio astronomy / physics experiment, so the exact details are not too important so long as they are all the same type. Can anybody help me find a source for these? Thanks John Murray jramurray@gmail.com

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Submitted by KA0GDW on Mon, 09/27/2010 - 23:19.

Is anybody using the TAPR Mercury receiver for radio astronomy applications in SARA ? I would like to contact anyone working in this area especially from the software development end of things. Please email me at ahar29@cox.com

LNB interface needed

Submitted by fieldsde on Sat, 09/04/2010 - 12:43.

John,
You didn'tⁱ say what function you needed, other than connectivity to the F connector -- so indeed, the set-top module you mention is probably useful and you can hack it. If you need to decode the signal, then the set-top box sounds most useful. But you want several identical units so it's better to buy something inexpensive.

For radio astronomy, you probably just need to detect energy or measure measure signal level. If it's for a student project in finding sources, then you can get 'satellite finder' boxes from ebay for maybe $15 each. They give an audio tone and meter indication of signal strength. I can tell you how to power and connect them if needed.

If you want to convert RFⁱ signal (C or Ku band)to a DC level, then you can amplify the signal using a Radio Shack in-line amplifier, followed by a (diode/capacitor) diode detector. You can measure, plot, or digitize this signal.

Good luck with the project -- let us know how it works out.

David Fields
www.roanestate.edu/obs

LNB interface needed

Submitted by jramurray on Sat, 09/04/2010 - 18:00.

Hi David Thanks for your reply. My experiment is basically a cosmic random bit generator. By cosmic, I mean that the randomness comes from both ends of the universe - the very large and very small. I want to see if the string of bits generated is truly random or has a fractal structure. The experiment has the following components: A macrocosmic noise source. This is a radio telescope dish pointing out of the galactic plane and picking up extra-galactic noise. To minimise local noise I use a quad-LNB in my dish. These noise outputs feed 4 Schmitt Triggers to convert the analog noise into a series of 1's and 0's. I use electronic logic circuitry so that the signal that I look at is only when all four inputs agree on their output either a 1 or a 0. A microcosmic noise source. This is basically the combined outputs of four home-made calibrated Geiger counters, giving a series of random 1's and 0's, this time from microcosmic nuclear disintegration These two random signals interact with each other using and exclusive-OR gate. If, at a moment in time, both noise sources say the same thing (both a 1 or both a 0), the XOR gate gives out (say) an 0 and if they disagree gives out a 1. The ex-OR o/p is my final ultra-random noise source. So my result is a fairly high frequency binary noise source with its roots in both the microcosm and macrocosm - both ends of the universe. This links on to my computer. I examine it to see if there is any fractal structure in the noise - that is, I see if patterns are repeated at a varying degrees of scale. So it is all up and running - apart from the RF units. The ones that I have (Sharp C77G74 satcans) stop working after about 20 mins. I am not sure that I have them connected up correctly but have had no luck in tracking down a data sheet for them. This is why I am thinking of replacing them Oh, I also have a small problem with instability in some of my op-amps, but I'm pretty sure that I can fix that OK. I'm very keen to get it complete and get on with the maths side of things! Regards John

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