[time-nuts] Some additional RTFG learnings

John Ackermann N8UR jra at febo.com
Tue Feb 20 09:54:12 EST 2007

Hi --

I'm doing some stability comparisons of the RTFG-m-RB and RTFG-m-XO units.

I fired up two RTFG pairs (thanks to Jim Miller for lending me his
units) with the 10 MHz and cross-over interface cables in place.  The
units fired up normally.

I did a 24 hour frequency stability run of the RB units measured against
each other, and all I learned in that time is that either (a) the RBs
are not actually GPS disciplined, or (b) the loop time constant is
longer than a 24 hour data collection will show.  After doing the XO
run, I will rerun the RBs for a longer period to see if there is any
sign of discipline.

Then, I disconnected the RB units so I could activate the XOs to run the
same test.

I thought the behaviour on doing that was worth noting:

1.  Disconnect the 10 MHz reference cable.  RB stays in "ON" mode, XO
goes to "FAULT."

2.  Disconnect crossover interface cable.  RB stays in "ON" mode, XO
stays in "FAULT" and "NO GPS" comes on.  But there is signal at the RF
OUT connector.

3.  In about 30 seconds, XO "FAULT" and "NO GPS" go off, "ON" comes on.

So, the XO is definitely testing for the presence of the 10 MHz
reference input signal, and becomes unhappy when it goes away.


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