Hello All -
Here is a link that describes the GPS modulation. You do not need the
1 pps to lock the 10 MHz oscillator to the atomic clock in the
satellites.
http://www.kowoma.de/en/gps/signals.htm
If you look at the block diagram you see PN code modulates the carrier
at
the 1.023 MHz chip rate. This is done by BPSK modulation of the carrier
with the PN code. It can be done simply with a double balanced mixer.
This spreads the signal with PSK at the chip( i.e. code clock) rate.
Note also the modulo - 2 addition of the data to the code sequence.
This called code inversion
modulation. After de-spread of the code in the receiver - the signal is
then simple BPSK and
may be demodulated by a Costas or Squaring Loop to get at the data
message.
The obtain precision frequency needed I believe the T bolt simply locks
to the chipping rate
using some form of Delay Lock Loop. It is NOT at PLL. There is no need
what ever to
deal with the 1 pps using this method. The internal 10 MHz oscillator
is controlled by this locking circuit and
is part of the code correlation loop.
I am not going into a tutorial on this, the the block diagram is
essentially the same as a K band
microwave data and timing system I did for the military in 1976. It was
good for 7 nS for a
100 dB dynamic range - it was a terrestrial link with a 20 Watt TWT
transmitter among other
expensive goodies.-
For those interested -
Look up
"Direct Sequence Spread Spectrum Modulation"
"Delay Lock Loop"
and also see "Spread Spectrum Systems" by R. L. Dixon. The first
real book in the public domain on spread spectrum.
However there is a ton of info in the literature for those interested.
GPS receivers use the same ideas albeit in digital implementation.
-73 john k6iql
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