[time-nuts] Clarification from a new member

[Dennis Tillman]

In my introductory email to the group, I mentioned that I was disappointed
in the GPS receiver I built from James Miller's design. 

I must clarify what I said with apologies to James for any misunderstanding
I might have created about his design! 

The receiver has an intermittent problem and I have not been able to track
down the cause. The measurement of time to this level of precision is new to
me. As of now, I have few pieces of test equipment suited to the task. What
I do have, I either built, or bought broken and repaired. The problems I am
experiencing with the GPS receiver are almost impossible to track down
because they are intermittent, they occur infrequently, and they involve
measurements to a level of precision I am not well equipped to make. 

At this point, I do not know what is causing these brief losses of
stability. They last for less than a few minutes as near as I can tell. My
next step, which is to try to monitor the output voltage of the PLL and
correlate it with the loss of stability, requires a way to log voltages.
Unfortunately the two GPIB Digital Multimeters I own both broke before I
could do this. Until I know what part of my GPS receiver is causing the
trouble I should not speculate on the cause. 

What I can say is that I followed James design to the letter. It uses the
Rockwell Jupiter TU30-D140 Receiver, James' PLL PCB, the IsoTemp OCXO134-10,
and a Symmetricom 58532 GPS L1 Reference antenna mounted on my roof and
connected to the receiver through low loss cable. The entire circuit is
professionally mounted into a Tektronix TM500 Prototyping Plug-in that is
powered by a TM501 power supply that is, in turn, plugged into an
Uninterruptible Power Supply.

One feature I wish this design had is an indication of when the output is
locked to the GPS satellites. I must admit, I could not figure out a simple
way to do this. I have since then come across a circuit that purports to do
this. However, until I solve the intermittent problem I have been reluctant
to add this circuit to the design.

Dennis

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> * Two years ago I built my own GPS frequency standard based on the 
> design by James Miller but it has been a big disappointment. I started 
> to suspect it was not reliable so I wrote a LabView program to compare 
> it to the reference outputs of two ArgoSystems AS210 systems I found 
> on eBay and restored. The LabView program confirmed my suspicions that 
> the GPS receiver was briefly loosing its stability for brief periods 
> several times a week.