[time-nuts] GPS signal simulator

[WarrenS]

----- Original Message ----- 
From: "Tom Van Baak" <tvb at LeapSecond.com>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Thursday, December 11, 2008 7:10 AM
Subject: Re: [time-nuts] GPS signal simulator


>> Tom
>> 
>> Thanks that should be very useful for software simulations.
>> 
>> The use I had in mind for the tool I described where for the next stage of testing. 
>> It can be used to test at the REAL Hardware level, using a 'perfect' GPS signal with 
>> no noise or with any type of desired controlled noise.
>> For example it is hard and time consuming to see how many ps of error 
>> your phase detector is adding or what the phase margin or noise gain is of the H/W PLL.
>> Is the power supply good enough or is it causing errors, etc 
>> When using real GPS data, the random noise will hide the advanced 
>> type of information you may want to take.
>> The other use of the Hardware simulator is for someone that wants to know how 
>> accurate their GPSDO is but does not have access to a source accurate enough 
>> to test their GPSDO.
>> 
>> WarrenS
> 
> Read a paper like this to appreciate the complexities involved:
> 
> http://tycho.usno.navy.mil/ptti/ptti2002/paper29.pdf
> 
> /tvb
> 
******************************
TOM

Thanks once again,
The paper is very helpful,  even if I can't  yet say I understand it all.
Agree, noise is a complex issue, GPS noise more so than most, 
because of all the many different types of contributing noise sources.
That is the reason I like to remove those unknowns initially for my H/W test.
Without adding the GPS noise to confuse the facts, it is very clear and easy to 
see, measure, and fix if desired the difference between say a sub ns accurate 
design and a micro sec unit. 
One of the questions I've needed to answers is just how good is good enough 
when it comes to making a high performance GPSDO.

Some of the self build units I've heard being used can be 100 to 1000 or more 
times worse than desired for best performance.

WarrenS