[time-nuts] GPS Timing receivers

Tom Van Baak tvb at leapsecond.com
Thu Oct 6 17:29:58 EDT 2005

> Hi everybody,
> I'm a final year student in TLC engineering, from the Polytechnic of
> The subject of my thesis is the GPS Timing Receivers in general.


> My main interests are:
> 1) Evalutation of GPS receivers performances, therefore I'm interested
> in test procedures.
> In this connection I've read the articles about the Test Bed at USNO
> in order to evaluate the M12+.

Yes, that's a good one.

> My questions are:
> - it is correct to evaluate a gps timing receiver just on the basis of
>their 1pps?

It depends very much on the application. Sometimes
evaluations include things like weight, size, power
requirements, acquisition time, price, TRAIM quality,
temperature coefficient, etc. But plain 1PPS is a good
start since it is the key feature that distinguishes a
GPS timing receiver from a normal GPS receiver.

Then there are a host of issues with evaluating
antennas, which although not part of the GPS
receiver, can be important to the quality of the
1PPS you are measuring.

> - it is possible to test a 1PPS using a TIC without a reference clock?
> - can you suggest me material (articles, proceedings and so on) about
> this kind of tests.

I think you need a reference. But for most 1PPS
analysis a rubidium standard and a 1 ns TIC is

There are several ways to quantify the 1PPS signal.
Almost all manufacturers specify things like signal
rise time and jitter (sawtooth).

But in some applications the actual accuracy of the
1PPS signal is what is important. That's what Rick
was measuring at USNO.

You could probably do the same with the help of
a calibrated tick at IEN in Turin. In this case the
antenna, cable(s), connector(s), etc. all have an
effect on the final result.

> 2) Timing Receivers architectures: I'm mainly interested in
> understanding how the 1pps is
> generated within the receiver. I've read a lot of IEEE docs, patents,
> manuals and application

This is further complicated since there are many
different receiver architectures and methods to
recover the timing. Look for subjects like single vs.
dual frequency (L1/L2), code vs. carrier phase,
real-time vs. post processed, precise orbits, all
in view vs. common view, etc.

> notes, but I haven't understood yet some details (maybe they are
> proprietary information!).
> Could you indicate to me any material that can be useful to my research?

If anyone finds some good articles let me know too!

> I hope to find some experts in that field, with whom to exchange
> opinions and experiences.
> I'm sorry for my poor English.
> Thank you very much.
> Kind regards, Albertazzi Michelangelo.


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