Hi I know I am repeating my self but reading Brian's experience with a FRS and the Shera controller, here I go again. Not having any luck contacting Brooks Shera, I did fool the controller with hardware changes and have very good results controlling a FRK-H. Comparing it with a Cesium, it is right up there limited only by my present measuring capabilities. Rubidium's are today available for less than $ 100 so are Tbolt's. How ever a Tbolt is a timing device and most of us have no ability or info to change it to a frequency device. Again I ask is there any interest to revive the Brooks Shera design with a few updates? Total hardware cost would be less than $ 40 not counting the GPS receiver. The result would be a world class standard for less than $ 200 counting all of you that already have rubidium's or high performance OCXO's it would be less than $ 100. An other advantage if done right it could also be a programmable digital loop to discipline a high performance oscillator to for example a not so hot short term rubidium. My problem to complete the project is I am an admitted ZERO when it comes to code and software. Bert Kehren In a message dated 7/27/2010 8:46:37 P.M. Eastern Daylight Time, [email protected] writes:
I read the article on PID on Wikipedia last night. I do not fully understand it, but I see/learning some of the relationship. I did a test on the FRS-C rubidium. The average frequency was 10 000 000.0025 hertz at the rubidium 10 turn dial dial setting of 255, and the control voltage out of the pot was 1.7900 volts. I recorded the frequency for a while and then changed frequency to see how long it took to get there. I changed the dial setting to 516 (3.5800V) and it took 8 seconds for the rubidium to change frequency and settle on a average frequency of 10, 000 000.0131 hertz. I did another test and the rubidium dial setting was 000 for a control voltage of 0.068V and the average frequency was 9 999 999.9933 hertz. The dial setting was changed to 721 for a control voltage of 4.9999V and the average frequency was 10 000 000.0216 hertz The measurements were taken with a HP5370B time interval counter referenced to a HP5065A rubidium oscillator. The data was recorded using a ProLogix GPIB adapter. The data was recorded in 10 minute intervals with the data coming in at one measurement a second. When the frequency was changed, I allowed 20 minutes between the recordings. Based on the above measurements, Said, can you recommend some starting point for the DAC Gain, EFC Scale, and the EFC Damping ? Also from previous measurements, I know this particular rubidium was at 9x10E-11 at 0.1 sec, 1.8x10E-11 at 1 second, 5x10E-12 at 10 seconds, 1.5x10E-12 at 100 seconds, 7x10E-13 for 1000 seconds, and 2.5x10E-13 for 10000 seconds - running on a Shera GPS controller - which the PIC was modified for this rubidium (it was changed from a 30 second time interval measurement to 120 seconds, and Shera changed the sensitivity of the PIC to 1X10-9/volt). Thanks to Don and Scott for the ops info. Thanks Brian KD4FM On 7/27/2010 2:57 PM, [email protected] wrote: > Hi guys, > > it may help to increase DAC gain to get faster recovery times from "bumps" > etc. > > On an OCXO, the frequency recovery from an upset should happen within a > couple of minutes, definitely less than 15 minutes to achieve frequency lock. > > The phase recovery (to 0ns offset) may take a couple of hours to do. > > If it takes a very long time to recover, then I think increasing the DAC > gain, or alternatively the EFCS and PHASECO together may help. > > Wikipedia has some good instructions on how to optimize PID type controller > gains to get the fastest response with minimal noise... > > Also, please make sure to disable temperature compensation when using the > external source, unless a thermistor is connected to the board, sensing the > Rb temperature. Otherwise the temperature compensation may add noise due to > it scaling the gain to huge values due to the missing thermistor. > > bye, > Said > > > In a message dated 7/27/2010 09:58:41 Pacific Daylight Time, > [email protected] writes: > > My experience is very similar to Scott's. I ran many hours with both an > LPRO-101 > and FE-5680A. The disciplining behavior and Fury settings were the same > for > either Rb. My biggest disappointment was the recovery time due to various > common > or intentional bumps or especially, after power loss. I also had to let > the > "system" settle in for a week before acceptable tracking smoothed out. Any > long > term slope to the EFC trace (gpscon) caused excessive hunting and this > didn't > settle down until the Rb was VERY stable. My gpscon TI and stddev was > virtually > the same as Scott's if I had EFCS set to 1.0 to 1.5 but recovery was > unacceptable (maybe 24-hours) so I usually ran at 2.0 or 3.0 with > slight degrading of stddev to around 3.2. This EFCS setting allowed a much > better settling time around 3-hours. > > DACG= 1000 > EFCS = 2 to 3 > EFCD = 50 (25 allows little better settling time) > PHASECO = 15 (I favor 10 Mhz over PPS) > Regards... > Don > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
