[time-nuts] 1PPS correction from HP58534A GPS Timing Antenna

Ulrich Bangert df6jb at ulrich-bangert.de
Thu Feb 18 08:00:17 UTC 2010


Don,

> One solution might be to send the receiver the custom NMEA 
> sentence which lets me set the antenna delay +/-nnnnnn 
> Nanoseconds. 

If something like this were possible, the receiver would do it for himself
(if called for)!

> A second approach would be to use a programmable delay line 
> (about $14 from jameco) to correct the the 1PPS by 85ns - 
> Timing Error from message. I would set the cable delay to 
> 85ns more then the actual cable delay to bring the 85ns in 
> the delay line calculation.

Yes! Has already been done, for example here:

http://www.cnssys.com/cnsclock/CNSClockII.php

In my DIY GPSDO I do it in the software.

Best regards
Ulrich Bangert

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Don Mimlitch
> Gesendet: Donnerstag, 18. Februar 2010 06:02
> An: time-nuts
> Betreff: [time-nuts] 1PPS correction from HP58534A GPS Timing Antenna
> 
> 
> I have been working with a HP58534A GPS Timing Antenna which 
> outputs extended NMEA sentences including a custom sentence 
> which specifies the Timing Error of the NEXT 1PPS Pulse as a 
> number between +00 and +85 Nanoseconds. I am wondering 
> whether using a PIC to correct each 1PPS pulse using this 
> sentence would be worthwhile to clean up the saw tooth in the 
> 1PPS and if so what would be the best way to correct each 1PPS.
> 
> One solution might be to send the receiver the custom NMEA 
> sentence which lets me set the antenna delay +/-nnnnnn 
> Nanoseconds. I would use the timing error plus the actual 
> cable delay to calculate the nanosecond delay to use for the 
> next pulse and send the cable delay sentence to the receiver 
> before the next 1PPS pulse. I have at least 100ms to send 
> this message at 9600 baud before the specified pulse arrives. 
> This should be sufficient time assuming the receiver acts on 
> the message immediately.
> 
> A second approach would be to use a programmable delay line 
> (about $14 from jameco) to correct the the 1PPS by 85ns - 
> Timing Error from message. I would set the cable delay to 
> 85ns more then the actual cable delay to bring the 85ns in 
> the delay line calculation.
> 
> I'm sure all the timenuts will have better or simpler 
> solutions to this concept and many different views on whether 
> it is worthwhile to do.
> 
> 
> 
>       
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