Yep, I leave the OCXO always on since I finished that circuit. The OCXO outputs a 6V reference, from there I go to the 10K pot, which goes to the EFC and ground/DAC (I have it wired so I can use a jumper to ground when not hooked to the DAC. The 5 MHz target is achieved around like 3.2-3.3V, so it's still pretty well centered, I don't remember how much pull the DAC has going up or down, but that part is okay I know because I've watched the EFC voltage and frequency on the scope.
I was talking about the resistors at P2 (R1 & R2). I think I can just use the TTL input instead of the AC coupled one. GPS is okay, it's a Motorola Oncore VP in fixed location mode. I also used a UT+ for a while before moving that to something else. Jason > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Bill Hawkins > Sent: Monday, January 15, 2007 6:58 PM > To: 'Discussion of precise time and frequency measurement' > Subject: Re: [time-nuts] Brooks Shera GPS Controller Help > > First, take your OXCO, heat it up, and use just a pot for the 0 to 6 > volt control range. Find out what control voltage is needed for the > proper frequency. The DAC can't achieve lock if it can't reach that > voltage. > > If that's all OK - the DAC output is within range - then find out what > AC input voltage is required from the OXCO to the board. 0.4 volts > sounds really low. What's all this about resistors? You can't achieve > lock if the board has no input from the OXCO. Are you sure > the GPS input > is OK? > > Did that help? > > Bill Hawkins > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On > Behalf Of Jason Rabel > Sent: Monday, January 15, 2007 4:28 PM > To: 'Discussion of precise time and frequency measurement' > Subject: [time-nuts] Brooks Shera GPS Controller Help > > You guys might have noticed a little bit I posted in another > topic, but > I figured it's time I started my own now that I have the setup all > hooked back up and running again. > > I'm having trouble getting the controller to lock the OCXO. The phase > reading only goes between about 10 - 155... Nowhere near the 800 that > means it is locked on. :( > > I have a Brandywine GPSDO that I used to coarse adjust the 5 MHz (both > hooked into my oscope), and I got it spot-on, probably way more than > necessary. I flip the Shera board to Mode 1, and the DAC voltage jumps > to about 1V and goes up and down between that and about 1.1V, slowly > back and forth. > > If I switch to Mode 2 or higher, then the DAC voltage will go all the > way through its -3V to +3V range, when it hits the top of the +3V it > jumps down to -3V and works its way up again. > > I'm using the A&A board, all my solder joints are good, even > the couple > that were the least bit questionable I fixed just to be 100% > sure about > that. > > I'm using a 5 MHz OCXO, with a tuning range between 0V to 6V. > I have S4 > closed, as my voltage increases the frequency decreases. On the A&A > board I have pins 1 & 2 jumpered together on P3. The GPS is a Motorola > Oncore VP, going through the TTL in. The OCXO is going through the AC > coupled input, after the resistors its still showing about > .4V p-p. Just > the plain output is about 2.5-3V p-p, I *think* I could just > use the TTL > in then? The notes says about 2V or less so that's what I > have it going > through the resistors. > > The first LED always stays lit signifying that the lock is > questionable > (obviously). > > My coarse adjust is a 10K pot, I did just add a 2K pot inline > as a fine > adjust, but have not re-calculated the R5 & R6 values. It is acting > exactly as before so I don't think that is the cause. But > tomorrow I'll > probably re-do the calculations for S, then also R5 & R6... > > My only guess is that something is wrong with the 5 MHz signal > somewhere... > The way the DAC voltage cycles makes me think it is just completely > ignoring something. > > If anyone is interested in the raw phase data, email me directly and I > can send them to you, but I don't know how helpful they will be. > > Jason > > > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts