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.