[time-nuts] GPS signal simulator

[Brooke Clarke]

Hi Warren:

Here's some info on a GPS signal generator made by Stanford Telecom  for 
testing their GPS ICs:
http://www.prc68.com/I/5001A.html
I'm sure it could be greatly reduced in size and complexity be replacing all 
the logic with a micro controller, but the RF part would remain.
There is a very strong correlation between the hardware and the ICD-200 GPS spec.

Have Fun,

Brooke Clarke
http://www.prc68.com

WarrenS wrote:
>     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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