Re: Transmitting high-speed PWM over RF

[Fabian Schwartau]

Hi Joshua,

the most important questions are:
Can you live with less than 50 M updates/second of the PWM?
How much error in the output PWM is acceptable?
If you need the 50 M updates/s and you want the PWM to be high precision 
(like 8 bit resolution or something like that), I would say: Forget it.
You are limited by the bandwidth of the ISM band (100 MHz or 80 MHz, 
depending on your location) and I am fairly sure that you are not 
allowed to transmit over the full band at the same time.
And what do you mean by "low latency"? Is one cycle ok? 100 cycles?
The only chances you have:
* Reduce the PWM frequency to something reasonable (like transmitting 
only 1 MHz updates over the air). You can of course build a system that 
gets the 50 MHz as input, processes it, output 1 MHz updates over the 
air, and a second system that converts that back to 50 MHz on the 
receive side.
* Do it the analog (hardware) way. Modulate the pwm on a carrier at 2.45 
GHz with AM/FM whatever, and demodulate it at the receiver. The 
demoulation would have to include some sort of rectification. Depending 
on the bandwidth and SNR you allow the transmission to have, your 
received signal will suffer some additional noise.
* Or go up in frequency. There are ISM bands at 5.8, 24, 61, 122, and 
244 GHz with plenty of bandwidth available ;)

Best regards,
Fabian

Am 02.08.22 um 18:45 schrieb White, Joshua J:
> First, let me apologize in advance if this isn't the correct forum for 
> this question.
>
> 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 rather new to the world of RF so it's possible there's a solution 
> that exists that I'm simply unaware of.
>
> Very respectfully,
>
> **
>
> *Joshua White*
>
> Precision Timing Systems Engineer
>
> Engineering & Support Solutions Directorate
>
> www.riversideresearch.org <http://www.riversideresearch.org/>
>
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