[time-nuts] 1 pps accuracy to UTC

[Ulrich Bangert]

Martyn,

> They are never within 20 ns.

as long as you look only at the two pps signals and without serial
communication to the receivers I would not bother about this fact. They may
have different antenna cable compensation settings which you don't find out
without talking to the receivers. 

> In fact even just 1 pps signal has about 50 ns jitter on it.

That is surely a bit above the specs! Is this true for BOTH pps signals? How
did you measure this jitter? I suggest you connect the pps of one receiver
to the start channel of your SR620 and the internal reference to the stop
input. Note that you cannot do this by any of the counter's switch settings,
you really need to route a cable from the reference output to the stop
input.

50 ns is a value that were ok for the older 8 channel Oncore receivers. The
M12+ should be better by at least a factor of two.

> I have two receivers running off the same aerial through a 
> GPS splitter.

You do use equal cable lengths between the splitter and the two receivers,
don't you?

Best regards
Ulrich Bangert 

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Martyn Smith
> Gesendet: Montag, 3. August 2009 15:02
> An: time-nuts at febo.com
> Betreff: [time-nuts] 1 pps accuracy to UTC
> 
> 
> Hello,
> 
> I may have asked this before, but still haven't got an answer.
> 
> The Motorola M12+ or M12M quote 20 ns accuracy to UTC.
> 
> I have two receivers running off the same aerial through a 
> GPS splitter.
> 
> If I measure the 1 pps signals on my SR620 counter (single 
> shot), they are 
> up to 100 ns out.
> 
> They are never within 20 ns.
> 
> In fact even just 1 pps signal has about 50 ns jitter on it.
> 
> I've tried this on many GPS receivers.
> 
> So how can they quote 20 ns, when two of them are up to 100 ns out.
> 
> Has anything got good results from the 1 pps signal output?
> 
> Any ideas
> 
> Martyn 
> 
> 
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