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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