> 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:
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.
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.
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.
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.
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.