[time-nuts] Some additional RTFG learnings

[TheInfamousFlavio at hotmail.com]

I got similar results in that the rb oscillators are not GPS disciplined 
after a 72 hr run.

I started off by manually offsetting the frequency of a warmed up rb unit by 
doing a manual adjustment to the rb oscillator via the manual adjustment pot 
so that it would be approximately 0.0050Hz off of my GPSDO.  Then I let it 
run for 72hrs and no change to the oscillator.

A few interesting things I discovered:

1. there is the unit is putting voltage to the electronic cfield connector 
of the rb oscillator.  I discoved this when I tried adjusting the oscillator 
when it was outside of the case.  When I put it back in the case an entirely 
different frequency displayed then when I put it back in the case.  When I 
manually adjusted the cfield pot on the rb oscillator, the unit did NOT 
compinsate for the manual change...which lead me to believe that there is no 
disciplining happening on the RB unit side. Although there might be 
potential for it to happen because of the  voltage to the cfield pin ... 
perhap some sort of initialization command is needed.

2. Both the XO and the RB unit can be in operational mode simulataneously. 
On the Interface xover cable, I simply disconnected pins 1 and 5 (the 
outside pins of the top row).  A simple +seems to control the A/B behavior 
of the XO and RB units.  So both units display "NO GPS" off and "ON" lit.

3. There a little BCA shorting wires a few places on both RB and XO units. 
The RB unit has BC jumped at each of these locations and the XO unit has AC 
jumped.  W201 determines from which points the unit takes the signal from to 
and from the oscillator.  W202 and W203 determine the to and from for the 
GPS receivers TX and PPS signal at the interface.

4. You can xover the interface with only pins 2 and 6 on the XO to pins 4 
and 9 on the RB. This simply send the GPS receiver's TX and PPS in the XO to 
the RB unit. By doing this both units will have 'NO GPS' off and 'ON' on.

5. Grounding the CPURESET doesn't seem to make a difference.

Does anyone have an idea of what PLDENB might mean?





----- Original Message ----- 
From: "John Ackermann N8UR" <jra at febo.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Tuesday, February 20, 2007 10:00
Subject: Re: [time-nuts] Some additional RTFG learnings


>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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>
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