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My team and I are working on a chipsat and we are planning on launching it to LEO, we've also planned using bpsk.

However our use case is a bit different, all we need once it is in LEO is a confirmation that that the radio is still working.

In this case, what is the fair value of SNR that we should require?

Edit: I should have phrased some parts a little bit better.

By working I mean that we need to know if it survived, what we actually plan to do is have the chipsat renter the earth, and "land" in the sea for instance, however as it is reentering it'll be traveling at extremely high speeds and exposed to extremely high temperatures ( we will have a heat shield and other precautions to account for these ).

So once it lands we want to know if all the components survived this harsh exposure, so one way we figured would just be if it is possible for us to send a signal to a ground station (we'll be using a SDR receiver so we'll probably use something like GNU Radio to analyse what we receive). But this also means that, the data we need to send need not be too complicated. That is we just need to send a couple bytes for confirmation.

Aamod Varma
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    Am I using Shannon-Hartley Theorem and thermal noise correctly here? The SNR tells you the possible data rate for a given bandwidth. It can be 10 or 0.1 and you can still communicate, it's just that it's a lot slower with lower SNR. So right now there is no "correct" answer to your question. Please add some details! Primarily, what is the lowest data rate you can accept? Do you just need a couple dozen bytes during a pass for confirmation? How will you track, receive, and record the signal for analysis? – uhoh Dec 08 '21 at 09:03
  • Presumably you'll use an SDR receiver and digitally record a large bandwidth, then you can process offline looking for the right Doppler shift vs time that pulls out a detectable signal. – uhoh Dec 08 '21 at 09:04
  • "all we need ... is a confirmation that the radio is working" contains all the important design goal to answer your question, but unfortunately is poorly formulated. What is your definition of "working"? BER? – Ng Ph Dec 08 '21 at 09:11
  • Thanks for the reply, I have edited the question to give a bit more context. – Aamod Varma Dec 08 '21 at 11:45
  • If you do not have constraint on time (storage), just send an alternating sequence of 0 and 1. I would say that an SNR=-3dB would be enough, even lower if you can afford a long enough capture of the signal. If your receive gear is calibrated, you can verify your Tx signal level, baud rate and frequency shift without even having to BPSK demodulate (there is nothing to demodulate in fact!). You can add a marker word at repetitive fix positions if you wish. Space them far away though. – Ng Ph Dec 08 '21 at 14:20
  • Not sure that this is an SX related question though. – Ng Ph Dec 08 '21 at 14:24
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    @NgPh there are plenty of radio hardware and signal questions here, this one's certainly on-topic. – uhoh Dec 08 '21 at 14:52
  • @uhoh, this is essentially a question about checking whether something on Earth is still working. The fact that it is a satellite falling back to Earth is the only link with "Space". What is peculiar is the decision to use a (terrestrial) radio link to check that it is still working. The question header is very misleading. You don't need to know that it is falling from LEO. – Ng Ph Dec 08 '21 at 17:37
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    If' you're planning to use BPSK anyway, pick a primitive polynomial in x^20 or so, broadcast it at 1 Mbps, and you'll have a lovely timing signal to send up and back down through a simple transponder to get range and velocity measurements you can use to determine the orbit. – Ryan C Dec 08 '21 at 19:00
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    @NgPh When/where did the cosmonauts fight wolves? hint: it wasn't in space :-) – uhoh Dec 08 '21 at 22:43
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    @uhoh, I must (reluctantly) concede ! – Ng Ph Dec 08 '21 at 22:54
  • @NhPh, As much as we would want to know if it's functioning back on earth, can the same method be used successfully to check if the radio functions whilst in space? – Aamod Varma Dec 09 '21 at 03:55
  • That's not what is written in your question. On Earth, your satellite sits still, in LEO it moves. On Earth, it may not be in line of sight with your station, it may be upside down, it may be wet. BTW, in space you want to use it. Back to Earth your goal is just to test it (or to find it?). If your problem is ill-defined, the solution may be a bad one. – Ng Ph Dec 09 '21 at 08:36
  • Once we launch it and it's orbiting, we want a confirmation that it's still functioning, and once it comes back to earth given that its upright and no other factors other than that of reentering has affected it, we would want another confirmation. Also back on earth as well we just want to test it, at least initially. I assume finding can be tedious. – Aamod Varma Dec 09 '21 at 11:06
  • Fair enough, it is your problem (although I can't understand it). – Ng Ph Dec 09 '21 at 13:12

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