[time-nuts] GPSDO Alternatives

Bob Camp lists at rtty.us
Wed Dec 5 21:45:03 UTC 2012


The TBolt does a resolution somewhere better than 0.1 ns. It (in some cases)
has been shown to hold better than 1 ns stability. That would be hard to do
with a low resolution timing setup.  

Some seem to like 100 seconds as an averaging time, others seem to want
something longer. If you have an Rb, you would certainly want something much
longer (days). Most modern setups step through a number of different time
constants and stop when things get out of hand. The one on the bench in
front of me is sitting at 8,000 seconds.

A 1.0x10^-12 goal is often tossed around for this sort of stuff. A 1 ns
timing accuracy (resolution would need to be better than the accuracy) would
get you to that goal in 1,000 seconds. That's in a perfect world. In a noisy
world you likely would have to wait a bit longer. TBolt to TBolt comparisons
do hit that sort of goal well short of 10,000 seconds (but rarely short of

This all comes down to a "what is your objective?" sort of thing. You can
not simultaneously decide you want to do 10X better than a TBolt, but that
an approach that's 10X worse is ok. (Thus my reference to managing the
feature list). If you are going to price the design against a $130 (or $200)
item, then you should also spec it against the same item. To spec compare it
one way and price compare it another way simply isn't being honest.

Design is so much fun....


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Volker Esper
Sent: Wednesday, December 05, 2012 4:25 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] GPSDO Alternatives

Am 05.12.2012 18:31, schrieb Bob Camp:
> Hi
> If the intent is to come up with something in the same league as the TBolt
> there are a few other things you will need:
> 1) Something to compare the two pps signals to within 0.1 ns....

Following Ulrich Bangerts suggestions, that a loop time constant should 
be at about 3 hours (GPS disciplining an OCXO), do I really need that 
resolution? Ok, the more accurate, the better. But the question is: can 
I reduce this requirement when using long time constants (10000s)? The 
ratio then is 10E14...


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