Because the 96K attachment needs moderator approval I am sending it again without attachment. It is the one I posted before and shows clearly the frequency jumps. So here is the rest of it. Magnus Sorry but I disagree with your statement. First and foremost we have to accept that these devices are not intended for time nuts (metrology). Already my first 1985 FRK monitors the cell current and adjusts the C field accordingly. The HP 5065 does not since it is not intended for the same market, it relies on its temperature control of the total A12 assembly. A closer look at FE specs you will notice the following statement " including frequency over or undershoot at any fast or slow temperature slew rate". How do you think they do it. In the case of units that have a DDS in the control loop they do it with the DDS. How else do you explain the attached plot. Again my apologies for not remembering who posted it. I noticed the jumps and mentioned them when I first took a look at the 5680 I did use temperature control in a crude way using what I call the Bang Bang fan control on an ATT FRS heatsink. My YSI did not register any changes but the 5680 noticed and was visible using my Tracor 527 E. The 5680 is not a unit that we will use it turned in to a distraction but we did the controller for time nuts. Our focus when it comes to temperature control is on the FRK that is why Juerg who focused on the 5680 only uses a heat sink. Working out of a basement that is next to a garage data in the winter looks a lot more stable than now. We monitor the tuning word which has a resolution of 6.8 E-13 and when you see no change over long time periods in January and changes now exceeding E-12 now to start asking why. The differences are garage door is open more often and the sun shines part of the time directly in to his basement lab. When the loop is in the long time constant mode to take advantage of the GPS accuracy resolution which increases with time, jumps by the 5680 DDS are no help. It all depends what ultimate accuracy time nuts want out of the 5680. A good fan control along with a fixed setting the temperature ADC input used for frequency control will yield best results. Work by time nuts will help we are not going to do it. The reason is we are totally tied up with work on using the FE 405 B. I stumbled by accident on to it and bought some for testing. Initial tests show for me unbelievable performance specially when it comes to ADEV. It is perfect for GPSDO applications since it is all digital control with a step resolution of 6 e-15. How ever it is also not all perfect since I did detected jumps that I could not explain. Since our testing capabilities are limited I did make Tom aware of the unit and he has now caught the bug. http://leapsecond.com/pages/fe405/ . We think we have traced the problem to again frequency control using oven current have disabled it and hope to have better data to prove that the 3 E-12 jumps are due to the current monitor. Stay tuned. Hope it does not change the ADEV. Not many of you have OCXO's with that low ADEV. We are also using the controller for this device and results look very promising. That is why we call it the Universal Controller. In the future it will control many other devices. But for now please those of you that have the equpment and the expertize focus on the FE 5680 A to make it a viable low cost house reference for a large # of time nuts. Bert Kehren
In a message dated 6/28/2014 3:21:48 A.M. Eastern Daylight Time, mag...@rubidium.dyndns.org writes: Hi, I fail to see what the benefit is of removing this unless a better temp compensation scheme is used. It is not likely to interfer with the external loop as it reduces the midterm noise that is systematic. It does add some higher rate noise but that is quantization errors of the systematics it reduces. I like to see measurement that support the claim and I am skeptic. As I see it you give the external loop more systematic noise to dampen and the tighter loop you make the more you will expose. Cheers, Magnus <div>-------- Originalmeddelande --------</div><div>Från: Scott Newell <newell+timen...@n5tnl.com> </div><div>Datum:28-06-2014 03:50 (GMT+01:00) </div><div>Till: time-nuts@febo.com </div><div>Rubrik: [time-nuts] DIY FE-5680A lobotomy (disable temp compensation) </div><div> </div>Bert asked me to send an update on the FE-5680 tempco mod progress. It appears that the FE-5680A temperature signal (or maybe it's really a current sense signal?) can be disabled by removing a single 10k 0805 surface mount resistor. Using Elio Corbolante's terrific high-res scans, I've noted the resistor location: http://www.n5tnl.com/time/fe-5680a/lobotomy.png Why would you want to disable temperature compensation? As we've seen, the unit's firmware will adjust the DDS frequency as the temperature signal changes. If you're using the '5680 inside a control loop, it's likely to conflict. By removing the resistor, that channel of the 12 bit ADC will be tied to ground through an existing 2.21k resistor. The unit will see a constant 0 counts from the ADC and assume it's really cold. I modified one unit and monitored it for a few hours over a range of temps, running it nice and hot with no heatsink, then blasting it with a fan and placing it on an ice-cold heatsink. I observed no change in the DDS tuning words. It's a really easy mod--remove four screws, set aside the insulator sheet, and apply your hot leucotome/soldering iron. I've also found a simple mod to replace the temperature signal with the output of the unused trimpot. This allows you to simulate any temperature you want. If there's any interest, I'll set up a test and monitor the DDS tuning words as the unit's firmware tries to adjust to the fake temp signal. -- newell N5TNL _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.