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First, let me apologize in advance if this isn't the correct exchange to post this question on.

I have a 50 MHz PWM signal (it's actually a 50 MHz 50% DC clock with a 1PPS clock embedded with PWM) that I would like to transmit over the 2.4 GHz ISM band with as low latency as possible. My original thought was to digitize the clock with a high-speed ADC, then stream the samples to GNU Radio and transmit via SDR, then recover on the receive side and playback the samples with a high-speed DAC. The problem I'm running into is that the only capture cards I've been able to find capable of running at the sample rate needed (>500MS/s) and streaming in real-time to GRC are prohibitively expensive ($8000+).

My question is, is anyone aware of any alternative methods of transmitting the 50 MHz PWM over ISM? I would be willing to entertain a different method of streaming to GRC or an entirely different setup. I don't know of any radios that could take the signal as input directly and transmit it, then receive it and output it directly, but admittedly I am new to the world of RF so it's possible there's a solution that exists that I'm simply unaware of.

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    $\begingroup$ Is this perhaps an X-Y problem? Why do you need low latency if the two signals are both purely periodic (50 MHz and 1 Hz)? Would it be possible to keep the 2.4 GHz carrier accurate enough in phase/frequency so as to convey just the pulse-per-second and reconstruct the rest from that via a PLL/divider circuit? $\endgroup$ Aug 2 at 18:37
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    $\begingroup$ You've cross-posted this also on electronics.stackexchange.com/questions/629768/… ; cross-posting is slightly frowned upon, and honestly, this is not about amateur radio, and a bit too specific for being about the theory and general technology behind radio, so I'd argue, electronics.SE was actually the right place to ask. $\endgroup$ Aug 3 at 13:57
  • $\begingroup$ I will take a SWAG: Why not have an oscillator generating the PWM at the remote and send periodic sync pulses, these could be time adjusted and use a lot less bandwidth and be more reliable. $\endgroup$
    – Gil
    Aug 4 at 0:51

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Wow, I can't believe this was down-voted. This is a great question and welcome to the forum aerophage, it's great to have you here. I would use a mixer and local oscillator or a few of them to get your signal to another frequency. When you mix 2 signals together you get the sum and the difference, one of which can usually be filtered out, so you get to pick. For example (and I don't know the whole story here) I would mix the 50 MHz with 48 MHz or something like that, and you get 2 MHz and 98 MHz, filter out the top and you are left with the 2 MHz signal which you can sample so much easier and continue processing from there (or make it 500 kHz or whatever you want). At the receiving end you do the reverse and mix it again to get 50 MHz or you synthesize it based on the sampled data. Another method is to mix it with let's say 300 MHz so you get 250 and 350, keep the top and now mix with 2050 so you get 1.7 and 2.4 GHz. Significant filtering will be needed to get rid of all the harmonics or you could cause interference. Those mixers are only a few $, and RF tools are cheap these days. I'm not sure if the 1PPS signal will make it through, it may need its own processing path and get mixed in. It doesn't sound like you need a high quality reproduction of the original signal, but the timing seems to be important. One thing I didn't tell you about is that there will be clock drift that will still mess this up so you have to account for that but I'd need to know more to think of a good way. You can't use 2x 50 MHz clocks, one on either side? Tell me more and I'll give you more ideas.

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  • $\begingroup$ @Marcus Müller I saw your answer in the other electronics section, it's actually pretty good. Better than my answer. $\endgroup$
    – pgibbons
    Aug 3 at 19:05
  • $\begingroup$ Thanks! Yours isn't bad either. $\endgroup$ Aug 5 at 19:07

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