[time-nuts] Environmental sensor recommendations

Bob kb8tq kb8tq at n1k.org
Fri Apr 6 10:25:28 EDT 2018


Hi

Since the DAC is integrated into the *guts* (FPGA) on the board, there really isn’t a way to
pull it out. There *might* be a way to feed it a better reference (which likely is the bigger 
issue). Since there are no schematics for a TBolt there’s not much of a way to do this or that.
If you *did* put in a new DAC, you would need to re-write the firmware to match up with that
part. Again you hit the same wall. There are no copies of the firmware source code “in the wild”.
You would have to figure out how to dump and reverse assemble the code that’s in there. 

Bottom line - since it’s a GPSDO and locked all the time …. not a big deal. If you used it in 
holdover, then it might be a big deal.

Bob

> On Apr 6, 2018, at 12:40 AM, David C. Partridge <david.partridge at perdrix.co.uk> wrote:
> 
>> The OCXO is not the temperature problem with the Tbolt. It is the DAC.
> 
> So is there a better one that can be used to replace it?
> 
> David
> 
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of ew via time-nuts
> Sent: 05 April 2018 10:43
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] Environmental sensor recommendations
> 
> I respectfully disagree. The OCXO is not the temperature problem with the Tbolt. It is the DAC. Again this is not a product developed for time nuts it did an excellent job for its intended purpose. Over a year we worked on the Tbolt using HP 10811, OSA 8600, FRK Rb, M100 Rb with excellent Warren support.
> Using up to 40 000 seconds and 6 E-17 per uV we probably know more about the Tbolt than any time nut. The DAC on the Tbolt is worse than 1 E-10, we have experimented with temperature control of the board. As a matter of fact the OCXO contributes to a certain amount of temperate stability.
> Attila visited Juerg and me on my Europe trip and observed 3 Tbolt's, original, 8600 and M100 in operation. Tracor 527 showed the jumps of the original.
> We plan on using the OCXO's pulled as offset OCXO's on our latest D/M project.
> Bert Kehren 
> 
> In a message dated 4/4/2018 11:46:09 PM Eastern Standard Time, holrum at hotmail.com writes:
> 
> 
> Lady Heather has a very nice temperature control PID in it (designed by Warren Sarkisen). It was originally designed to stabilize the temperature of a Thunderbolt GPSDO. The standard Thunderbolt OCXO is rather temperature sensitive. 
> 
> The standard/simple implementation involves sticking the Thunderbolt in a cardboard box with some thermal mass and baffling. Heather then PWMs a fan (at 1 Hz, using the serial port modem control signals and a DC solid state relay) to mix room temperature air into the box. It can control the temperature readings to around 0.01C with long term RMS errors in the low microdegree range (absolute accuracy depends upon the temp sensor).
> 
> -------------------
> 
>> I would suggest that if you are looking at taking temperature sensor 
>> data
> and attempting to control some type of heating/cooling device that you implement a PID loop for stability.
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