[time-nuts] Some additional RTFG learnings

[John Ackermann N8UR]

I started data gathering of XO vs. XO about three minutes after yanking
the interconnects as described below (but after the units had been
running in GPS locked mode for well over a day).

There is definitely a stabilization period required after the XO becomes
operational; on this measurement, the one second tau is around 4x10e-9!
 I'll try to get an idea how long it takes to stabilize and report back.

John
----

John Ackermann N8UR wrote:
> 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.
> 
> John
> 
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