[time-nuts] Different Survey Results

Bob Camp lists at rtty.us
Fri Aug 20 12:04:01 UTC 2010


The TBolt is rated to 70 C. You probably are ok running them at 50 C. The OCXO does not mind the heat and there's nothing else in there that has any noticeable heat rise.

If you text search for "pool of mercury" in the archives you will hit a thread that goes into the details (and impracticality) of very long thermal time constants. The wood box with foam is a good way to go. Past that active control makes sense.


On Aug 20, 2010, at 3:23 AM, Arnold Tibus <arnold.tibus at gmx.de> wrote:

> Peter,
> My TB is running continuously during months.
> It draws about 7 W using the black PWR-supply proposed by Tom (TvB).
> In the room at about 22 °C it does show 32.43 °C, I never passed 37 °C.
> So I would propose to net go beyond the 40 °C internal temp. reading. I
> will manufacture a wooden box with thick walls to stabilize the temp.
> Wood does of course not shield, but because the high thermal capacitance
> together with its isolation (moderate)it should result in a
> long thermal constant. Of course the temperature will come up, hopefully
> not surpassing 42 °C. Low temperature = longer lifetime.
> Your osc. Adev values are similar to mine, that should be ok (good).
> I can confirm the experience by Warren. I use 490 s,0.68 damp factor and
> a gain of -3.55 Hz/V actually resulting to
> @ 1 tau 5.096E-11,
> @ 100 tau 3.05E-11,
> @ 500 tau 6.43E-12
> @ 1000 tau 2.92E-12
> Osc. ADEV
> @ 1 tau 3.39E-09,
> @ 100 tau 3.45E-11,
> @ 500 tau 7.05E-12
> @ 1000 tau 3.32E-12
> read by Lady Heather, which does not mean that these values are exact!
> This with the original OCXO, perhaps with an external oscillator one
> could get better results, but I had no luck yet.
> The PPS does very seldom exceed +- 5 ns, normally it does move just
> around +- 2 to 3 ns. The DAC-Voltage changes are in the range of +- 3
> steps of around 25µV (a step presesents close to 8 µV)
> These are my observations, I hope it does help you.
> regards,
> Arnold
> Am 19.08.2010 23:59, schrieb Peter Krengel:
>> To John WA4WDL:
>> The coordinates out of my current (fixed) position  calculated by
>> the SirF GPS and the tbold during a 48h survey are different.
>> On a map this differences makes up a shift of up to 100m around
>> my true qth. With other words if I would (and could) use the tbold 
>> as a mobile GPS I would come off road at once ;)
>> To ws:
>> Thanks for the interesting answer and tips for modifying factory settings.
>> My tbold works in a good stable (temperature) environment. I tried out
>> to put it in a temp-isolated box but Osc temperature went up to about 50°C
>> (not too hot?).
>> Secondly I tried it without a box at normal 20°C room temperature (varying a little bit) and it showed OSC 41.75°C. 
>> What is the better choice?
>> It also got fine antenna conditions (mostly 8 sats are recognized having
>> signals between 38 and 48dBc) by using a roof top ceramic chip antenna (it has a inner preamp)  followed by a 20dB wideband amp and about 20m
>> coax. As I am located on a hill top it "sees" a 360° free sky down to 0° elevation.
>> I got the following results using factory settings after cold start and 10 hours running with my true (are they really my true coords?) qth coordinates saved after self-survey:
>> 1        tau  2.7E-09
>> 10000 tau  7.0E-13
>> My intension (of cause..) is to get the best out of the tbold in short and
>> long term stability.
>> The tbold isnt modified in any way running the original oscillator.
>> What do you think ?
>> ------------------------------------
>> To Mark:
>> I too got a LPRO rubidium but it I'm not very satisfied because of the need of long time warm up after power fail and the need of a heat sink.
>> In addition the tube wont last for ever and is used for 10(?) years...
>> Anyway I would like to compare both tbold and Lpro if the tbold is
>> setup best as possible.
>> Thanks and regards
>> Peter  DG4EK
>> _______________________________________________
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