[time-nuts] Building a GPSDO & trouble using Jupiter-T

Roberto Barrios rbarrioss at msn.com
Fri Feb 3 09:58:17 UTC 2012

Long time ago I built a Jupiter-T companion board that included the loop 
filter, divider and phase detector for the James Miller GPSDO. It also 
includes a PIC that monitors the NMEA strings and displays different status 
data via LEDs, and outputs data via RS232.


I used an ISOTEMP OCXO and it worked well.I also tried to implement a lock 
detection mechanism, first based on timing the phase detector and sencondly 
monitoring the swings of the EFC. I was not very happy with any of those 
solutions and finally gave up. Details are in the code.

Text is in spanish but you really don't need to read it, it is very, very 
basic for you time-nuts. If anyone has a suggestion for a better lock 
detection solution applicable here, I'd love to know about it.

Best regards,
Roberto EB4EQA

-----Mensaje original----- 
From: Tom Van Baak
Sent: Thursday, February 02, 2012 11:56 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Building a GPSDO & trouble using Jupiter-T

> This thread got started when someone asked if an analog PLL would work
> for building a GSPDO.  For that you do need timing pulses much faster
> then 1PPS.
> But the analog PLL are not the way to go for best accuracy.

Remarkably, the simplest and still one of the best GPSDO I've
tested was the 10 kHz Jupiter and analog PLL-based standard
by James Miller. It performed superbly. It's the 4th GPSDO at:

True, there exist some better GPSDO, and you need digital if
you want a hold-over feature, but I wouldn't discourage anyone
from trying the analog PLL method. The sheer simplicity might
more than make up for a few less ns. Miller's page is at:


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