[time-nuts] Question for my new GPSDO

[djl]

Tobias: along the path suggested by TVb, might I suggest something like 
a small heater/cooler for your car?
lots at https://www.amazon.com/s?k=car+cooler+6+pak&ref=nb_sb_noss
a simple controller such as

eBay item number:
192112054053
  can be applied as well.

and Bob's your uncle.
Don

On 2019-10-08 06:35, Tom Van Baak wrote:
> Hi Tobias,
> 
> Very interesting project you have. Not just that it's a fresh GPSDO,
> but interesting because you seem to be taking so much care in the
> design. A couple of comments:
> 
> 1) The need for ultra low tempco is more important if you expect your
> GPSDO to be in holdover often; less so if it is permanently locked to
> GPS.
> 
> One approach is to spend the money for low tempco devices and trust
> them; another is to monitor the temperature and apply calibrated
> corrections in s/w. I can't predict which is better, but don't
> discount the latter approach.
> 
> Still, either method will have to be verified with actual experiment,
> strip charts, correlation analysis, and ADEV plots. So I hope you have
> the test equipment at hand to measure these subtle effects in a GPSDO.
> 
> 2) I suspect one can spend a great deal of time picking and testing
> optimal parts in a GPSDO based on tempco specs. But at what point is
> it cheaper to just control the environment of the GPSDO board itself?
> 
> You mention opening lab doors and windows and such. Wouldn't it be
> simpler to spent time to design a box that is wind-proof, or
> fan-controlled; maybe even oven controlled? That way you can relax all
> your worries about exotic passive and active components and just build
> a controlled enclosure.
> 
> That could not only take care of temperature, but humidity and
> pressure as well if they were found to be sources of instability. One
> advantage of this approach is that the same box design could then be
> applied to any other T&F projects like distribution amps or phase /
> frequency counters that you design in the future.
> 
> 3) About sensors.
> 
>> many GPSDOs I have tested (e.g. Trimble Thunderbolt, STAR4) show info 
>> about the OCXO temperature
> 
> The Trimble Thunderbolt (TBolt) uses an onboard DS1620 temperature
> sensor. I don't recall it ever being called "OCXO temperature"; it's
> ambient board temperature. Perhaps because the board is inside a
> larger aluminum enclosure the board temperature is related to OCXO
> case temperature. But as far as I know the reported temperature value
> from a TBolt is definitely not the temperature of the crystal
> resonator itself.
> 
> /tvb
> 
> 
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-- 
Dr. Don Latham  AJ7LL
PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304