[time-nuts] GPS receiver local oscillator

[paul swed]

Well thats a heck of a tidbit to learn.
I built up hack multipliers and such to get some of the old GPS receivers
going.
The best was austron 2001. I did retire it as it was really getting to be a
pain to operate.
You had to know what your doing. Not sure I like that. Neo's have spoiled
me.
What was interesting was that somehow it made its way up to the MIT flea.
Picked it up for the chassis.
No antenna and such.
Powered it up and dealt with alarms. The lat and long on the box was the
Aricebo observatory in PR.
Pretty interesting how it could have showed up in Boston.
Reagrds
Paul

On Wed, Aug 15, 2018 at 8:15 PM, jimlux <jimlux at earthlink.net> wrote:

> 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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