Great comments. I can confirm the oven behaviors. The out is not needed. It is controlled from the micro and warms slowly at about 17 volts. Gets to 150 F after a solid hour as long as its insulated other wise it has a hard time keeping up with ambient air. The 10811 does heat quickly to the 85C. I have measured it and it is heating to 85. So unfortunately not my lucky day. Opamp would be a piece O-cake. So all that said time to move on. By injecting 10 MHz from a TBolt I hoped to get things running. Just to see. But I think I have a second issue. HP satstat and gps control report the OCXO warming up. Never gets to the hot point. Now the 108011 is out of circuit and per the 10811 manual I am supplying a 3.5V signal to the cpu. But it never changes state. The second issue was the bad 10811 has made the DAC goes to 100%. So far no luck in it changing. But of the ovens not warm I could see why the system would not adjust the EFC. I am hoping away from 100%. A system preset does tell the DAC to go to a mid range level but after some 10 or seconds it jumps back to max. I almost might believe I would need to do a fast dance. restart and very quickly tell it to write the data to eeprom. I am not that fast. Have been searching th net for clues about reseting teh dac. No luck. Regards Paul WB8TSL
On Fri, Dec 16, 2016 at 3:02 PM, Bob Camp <[email protected]> wrote: > Hi > > The “outer oven” on the Z3801 10811’s is simply a warmup heater to improve > performance when the unit > starts at -40C. When operated as designed, it is effectively “gone” in > normal operation. The 10811’s normal > oven circuit (“inner oven”) on the modified 10811 is still what does all > of the stabilization of the crystal. The > temperature stability of the Z3801 version is not significantly different > than the standard 10811 when measured > over a normal ambient range. Since our basements are rarely at -40C there > is not a lot of value to the "outer > oven" in the standard configuration. A proper outer oven / inner oven > combination would be designed and > configured very differently than what you see in the Z3801. The “boost > heater” approach does show up in > other gear, very little of it is in TimeNuts stuff. > > Why do it this way? The 10811 as built simply did not have enough power to > warm up properly from -40. At > the time, there was some thought that GPSDO’s would be deployed in > un-heated enclosures (that never happened). > To get the unit working, a number of “quick and dirty” hacks were employed > to hook the existing OCXO into > the Z3801 design. They were of a “fast time to market” nature rather than > “figure it out and do it right”. > > Bob > > > > On Dec 16, 2016, at 12:44 PM, ed breya <[email protected]> wrote: > > > > I had a reference problem on my Z3801A years ago, and ultimately found > that the opamp that controls the 10811 oven temperature was bad. I think it > turned out there was a bad batch of certain date codes. Replacing the IC > with an equivalent type fixed it right up, with no other changes or > adjustments. > > > > Also note that the the ovens are sequenced to avoid drawing too much > power from cold-start. As I recall, the inner one has to get up near > operating temperature to get things running ASAP, then its status signal > enables the outer oven driver (a switched-mode converter on the Z3801A > power supply board) to start - it takes longer to stabilize. I think the > inner oven should take maybe 20-30 minutes tops, to reach the spec range, > and the outer one gradually catches up over maybe an hour or two. > > > > The crystal is very sensitive to temperature until it gets to turnover, > so the frequency can seem way out of whack compared to its normal operating > point. The oven temperature doesn't have to be very far off to cause this, > so a failure in the inner oven control that throws it out of range could > cause problems. > > > > Ed > > > > > > _______________________________________________ > > 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.
