[time-nuts] GPS receiver local oscillator

jimlux jimlux at earthlink.net
Wed Aug 15 20:15:59 EDT 2018


On 8/15/18 2:20 PM, paul swed wrote:
> Wanted to add a bit to the conversation. At least in a number of older GPS
> receivers circa 1989-1994 the LO was indeed locked to a 10 MHz reference.
> These were the typical separate mixer and antenna systems. The first LO was
> 1500 MHz.
> That is an expensive way to go so I can see why whats described here is
> attractive to lowering costs.

Indeed -
one of the JPL GPS receivers has a 38.656 MHz clock used to latch the 
output of 1 bit comparators, which makes L1 alias to 9.476 Mhz, L2 alias 
to 9.392 and L5 to 16.770

Hard to get much cheaper. No microwave mixers.  Just bandpass filters, 
broadband amps, and a comparator at the end.

Frequencies chosen so that even in worst case Doppler, the offset is on 
the same side of zero.




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