[time-nuts] Re: DOXCO from Z3801

[Bob kb8tq]

Hi

The idea of an unheated cell tower was indeed what they headed towards when this oven 
was “designed”. Turns out there is a *lot* of hardware in a cell site that is very much not happy
at all when it gets below freezing. That killed the idea of the -40 degree cell tower on top of a 
telephone pole dead. However it was to late for the initial version that HP came up with. They
stuck with the heater. 

On a true double oven. The outer oven improves stability. It is set up along with the inner oven
and the design is optimized for both ovens. That’s not at all the case with this oven. It’s just a 
warmup heater. It actually makes the stability of the device worse in most cases. Yes that sounds
crazy. For all the deep math and examples of just *why* this is true …. head over to Rick’s set
of papers. It’s all in there …..

Bob

> On Dec 7, 2022, at 8:52 AM, paul swed via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Andy
> For what you are doing I am not sure the outer ovens really needed. Its use
> would have been for locations like Cel Towers and such that can be very
> poorly heated if at all. I might guess you could put a temp probe in and
> set it at some temp like 100 F and let it go. Or as I say not use it at all.
> Others will have stronger opinions.
> Regards
> Paul
> WB8TSL
> 
> On Wed, Dec 7, 2022 at 5:28 AM Andy Talbot via time-nuts <
> time-nuts at lists.febo.com> wrote:
> 
>>> I've been given a defunct Z3801 with a fully working ovened oscillator.
>>> The rest of the GPSDO circuitry is just junk and will be chucked, but I
>>> want to get the DOXCO running as a backup high stability reference here.
>>> 
>>> I've worked out the power connections for the oscillator and inner oven,
>>> and have powered it up with +12V & +24V supplies.   It's currently just
>>> warmed up and is happily generating a nice sine at 10MHz, with +0.3V (at
>>> the moment) t on the EFC.
>>> 
>>> I applied 24V to the outer oven earlier to see what happened, and
>> measured
>>> the thermistor resistance as it warmed, watching it fall from 110kΩat
>> room
>>> temp to 30kΩ where I stopped.  I know the controller for the outer oven
>> is
>>> in external circuitry, but a brief web search failed to show a) what
>>> temperature it should run at, To, and b) what the thermistor resistance
>>> would be at that temperature, Ro.
>>> 
>>> Does anyone here know these figures off hand, or do I need to go to the
>>> web and download the circuit and trace out the outer oven controller
>>> details.   I'll be doing my own controller circuitry, so just need To and
>>> Ro.
>>> 
>>> Andy
>>> www.g4jnt.com
>>> 
>>> 
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