I believe that there is more to the interface cable than a simple crossover -- I wonder if there are any pins that are jumped on one or the other of the connectors.
By the way, in the experiment I reported on earlier, the XOs seem to be running undisciplined as well, and are about 1 Hz off nominal frequency. There's definitely something else needed to make these things work properly. John ---- [EMAIL PROTECTED] said the following on 02/20/2007 02:33 PM: > 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" <[EMAIL PROTECTED]> > To: "Discussion of precise time and frequency measurement" > <[email protected]> > 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 >>> >>> _______________________________________________ >>> time-nuts mailing list >>> [email protected] >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> >>> >> _______________________________________________ >> time-nuts mailing list >> [email protected] >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> > > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
