[time-nuts] Environmental sensor recommendations

[Bob kb8tq]

Hi

Just to be very clear about this issue:

Your room temperature “moves” at a rate dimensioned in degrees / hour (like
2 degrees / hour) and the period should be out in the half hour to couple of 
hours range. Put another way, it’s a 1,800 to > 5,000 second sort of thing. 

Operating with typical loop parameters, a TBolt is locked to GPS past a few 
hundred seconds. The OCXO simply follows whatever the GPS happens to
suggest is correct. The temperature effects (whatever the source) are past
the GPS cutover point. 

Unless you are running the TBolt into something other than an OCXO, the 
loop will take out *any* of the temperature impacts on the output of the device. 
That’s just the way a control loop works. It’s how it was designed to work. It
also is (most likely) why none of this bothered the original design team. 

In holdover, you will see / do see / can see the impact of temperature. The
gotcha there is that the TBolt has a temperature sensor on it. In holdover 
that sensor “corrects” the EFC voltage. To the degree this process works, 
it takes out any temperature impact in holdover. Again, it’s probably why 
the original design team felt things were ok.

So, why when you change this or that (like to a different OCXO) does the 
temperature sensitivity plot change? Well, if the DAC / reference is the source
of the error *and* you reduce the sensitivity of the OCXO, the temperature
impact *is* reduced. Go to something like a normal 10811 with a 1x10^7 etc
range and the impact should go down by more than an order of magnitude. 
LH is *not* lying to you…..

What is a problem: You look at the plot on LH and conclude that the TBolt
is wandering around with temperature changes. That’s not what it’s telling you.
The only thing LH *can* observe with just a TBolt are variations that have 
been corrected for by the control loop. If the loop does not correct for them,
the DAC does not change, and LH has nothing to go on. With no data
to indicate a change, LH reports that nothing has happened. Again it’s not
lying to you. It simply can only do just so much with the information it has. 

None of this is to say that the various effects are un-interesting. They are 
fun to watch. What would be more interesting would be to be able to dig
a bit deeper. We already can go a lot further into a TBolt than any of the 
other commercial units. Complaining that we can’t go further is … well …
this is TimeNuts …. 

Bob

> On Apr 6, 2018, at 8:30 AM, ew via time-nuts <time-nuts at febo.com> wrote:
> 
> How did you measure temperature sensitivity
> Bert Kehren
>  
> In a message dated 4/6/2018 3:40:18 AM Eastern Standard Time, holrum at hotmail.com writes:
> 
>  
> I replaced the OCXO on one of my Thunderbolts with an Oscilloquartz 8663 and the temperature sensitivity went down by about 2/3, so I always assumed the main contributor was the OCXO. I didn't try mod-ing any other Tbolts. 
> 
> I also tried temperature stabilizing the power supply and it seemed to also have an influence.
> 
> -----------------
> 
>> I respectfully disagree. The OCXO is not the temperature problem with the Tbolt.
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