[amluto]

> Just one problem: you won’t find any SDR on the market that will claim to be able to sample a wave oscillating over a billion times a second.

This was true, but not any more. You can get truly impressive “direct RF sampling” or “direct RF conversion” receivers that are more than fast enough for GPS. For example:

Xilinx RFSoc: https://www.mouser.com/datasheet/2/903/ds889_zynq_usp_rfsoc_...

A nice National Instruments article: https://www.ni.com/en/solutions/aerospace-defense/radar-elec...

And their referenced off-the-shelf hardware: https://www.ni.com/en-us/shop/category/flexrio-custom-instru...

One might be forgiven for being a bit puzzled as to why NI thinks that direct RF conversion is cost-effective but nonetheless sells the device for $30k :) That being said, if I were prototyping a system that wanted phase-coherent wideband reception around 3 GHz and I had a proper lab and budget, I’d buy a few of these. If I were to go to production, I’d either wait for costs of a homemade board to come down a bit or see whether a traditional heterodyne receiver could do the trick.

Hmm. For military applications, if I were concerned about really advanced RF-seeking weapons pointed at me, a direct conversion receiver is probably great — there won’t be any leakage of the LO that an enemy device could try to detect.

[elevation]

> there won’t be any leakage of the LO that an enemy device could try to detect

Why would an LO be more of an issue than your sample clock?

edit: missing word

[AnarchismIsCool]

It's very hard to prevent the LO from leaking into the ADC input. Putting the filters in the right places would cause a lot of issues for the signal chain so a common workaround is trying to null it with a 180 degree out of phase LO signal.

[amluto]

I don’t know all the details of this kind of technology, but I would imagine that one direct RF receiver’s sample clock looks effectively identical to any other similar receiver’s sample clock. So if these devices become popular, then a military sample clock is indistinguishable from a civilian sample clock. In contrast, an LO is rather application-specific.

[londons_explore]

For military use, where you are trying to blend in with civilian equipment, either the direct sampling clock, or the local oscillator frequency, could be randomly chosen in quite a wide range at bootup and still have the device work.

In todays world with everything software reconfigurable, changing the sampling rate or local oscillator frequency is very do-able.

[codyd51]

This is amazing! I had no idea tech like this was available on the market. Thank you for the correction.

[kragen]

i agree!