[time-nuts] The 10811 double oven mystery

[Bob kb8tq]

Hi

Well, based on conversations with the people who designed the part, 
the outer oven’s only function was to take care of a potential cold end 
problem. At the time, the telecom guys were thinking of putting GPSDO’s
in systems with no heating on the enclosures. That idea died when they
ran into a variety of issues with the digital side of things at cold temperatures.

The issue isn’t the *sensitivity* as much as the simple fact that the 
10811 will not warm up at all from a really cold temperature. There just 
isn’t enough heater power. If you want to dig into just why a “jacket” like 
this is not going to give you super oven performance, the various papers
Rick published on his single oven are a good start.

Bob




> On Apr 8, 2020, at 3:53 PM, Jarl Risum <jarl.risum at gmail.com> wrote:
> 
> I have been puzzled by a mistake which has been published recently on this
> list and elsewhere as well. It concerns the operation of the HP 10811
> double oven TCXO used in the HP Z3801 GPSDO.
> 
> It is claimed that the outer oven is only in use during start up or during
> extremely low ambient temperatures and is not operating during normal
> conditions. This is not correct.
> 
> The 10811 outer oven circuit in the HP Z3801 is designed to maintainin a
> stable temperature around the 10811-60158 OCXO somewhere in the interval
> between 60 and 65 deg. C in order to reduce the 10811-60158 OCXO's
> sensitivity to temperature changes which – without the outer oven - is
> specified as 4,5 x 10 e-9 from 0 to 71 deg. C.
> 
> The HP Z3801 was made as a GPS disciplined timebase for synchronization of
> CDMA Cellular Wireless Land Network base stations and was required to
> maintain system syncronization for up to 24 hours in situations with
> failure of GPS reception. In order to satisfy this requirement, the HP
> Z3801's internal processor keep track of the gradual ageing of the 10811
> during normal GPS-disciplined operation and applies a calculated, predicted
> correction voltage to keep the OCXO on frequency during periods with no GPS
> signal (HP's Smart Clock technology).
> 
> A diagram and detailed description of the 10811 outer oven circuit can be
> found at KO4BB's manual collection under
> http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=02_GPS_Timing/Z3801.
> Pictures of the outer oven can be found at
> www.realhamradio.com/GPS_Frequency_Standard.htm.
> 
> In 2013 Warren Sarkison published an improved 10811 Outer Oven Controller
> with improved temperature regulation. Description and numerous references
> to his design can be found by Googling ”Warren S. Design 10811 Outer Oven
> Controller”. This circuit - or something similar - is much to be
> recommended if optimum operation of the dual oven 10811 outside of the HP
> Z3801 is considered.
> 
> Jarl
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