[time-nuts] GPS signal simulator
WarrenS
warrensjmail-one at yahoo.com
Wed Dec 10 09:03:25 UTC 2008
In my quest to keep improving my GPSDO, a simple test tool
that I find indispensable is a GPS 1PPS (or 100Hz) signal simulator
reference. Others may also find this useful because it allows testing the
PLL & DO in their GPSDO to Cs type accuracy using a standard OCXO.
The advantages of using the 1PPS GPS signal simulator instead of the
real thing for high accuracy test, is that it eliminates all the errors and unknowns
that come before the 1PPS signal so that the performance and limitations of
just the PLL and it disciplined oscillator can be quickly tested independently
of the receiver and the GPS signal.
This also gives higher accuracies than are available from the GPS system,
while using a relatively low accuracy oscillator for its reference.
The simulator generates the 1PPS signal from a divided down
standard 10MHz OCXO.
For advanced test a simple Phase modulated 'Noise' can be added to the
1PPS to represent the basic phase noise of the GPS receiver's 1PPS signal.
The phase & freq difference between the reference oscillator and the
tracked PLL oscillator can then be compared to any desired accuracy
and resolution limited by the noise, but not the accuracy, of the oscillators.
Now I am wondering:
Has anyone made or considered the tricks needed to simulate a GPS
RF signal in a simple and cheap way?
Something that could be used to send a 1PPS timing signal to a GPS receiver
for similar basic high accuracy receiver testing from the antenna to the 1PPS?
It would seem that this may be feasible when used with a receiver that can
output its 1PPS when locked to a single satellite? ? ?
WarrenS
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