[time-nuts] HP 10811 40 Hz low.

paul swed paulswedb at gmail.com
Fri Dec 16 16:08:13 EST 2016

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.

On Fri, Dec 16, 2016 at 3:02 PM, Bob Camp <kb8tq at n1k.org> 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 <eb at telight.com> 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
> >
> >
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