[time-nuts] PN sequence generation using GPS

[Hal Murray]

>> How long you can freewheel depends upon how closely the
>> clocks are synchronized.

> I always thought the receiver's clock kept itself sync'd via a phase lock
> loop with the transmitter.  So the transmitter timing could drift a bit
> "off" and the receiver would follow.  This system also automatically takes
> care of propagation delays perfectly 

In the context of this discussion (see Subject) I was assuming that both the 
transmit and receive clocks were normally locked to GPS.  I was commenting on 
the case where GPS wasn't working.

I think there are really 3 clocks in this discussion.
  One is the reference (say 10 MHz) that turns into the RF frequency.
  One is the chip clock, switching from one frequency to the next.
  One is the reset/init signal for the logic that generates the sequence of 
frequencies.

They are probably related like a watch has a second hand, minute hand, and 
hour hand connected by gears.  Once you get them started correctly, they will 
stay in sync.

A PPS signal from a GPS would provide a nice way to get started, but it needs 
a correction for the speed-of-light delay.  I don't know if finding that 
delay would be easier or harder than traditional methods for getting the 
receiver in sync.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.