[time-nuts] Re: Thunderbolts ...

[Charles Steinmetz]

Stewart wrote:

> A few days ago, Charles Steinmetz mentioned that even the "good"
> Thunderbolts with the 37265 OCXOs fall into two groups, one 100x worse than
> the other. Perhaps that difference is not due to the OCXOs themselves but
> to other parts on the board.

If that were true, it would mean that the actual EFC voltage in those 
units was varying with respect to the DAC voltage as reported over the 
Tbolt's serial port.  While not impossible (after all, we know almost 
nothing about the internal architecture of the Tbolt), for a number of 
reasons I think that is unlikely.

> We know that, during the production run, the high-resolution board
> temperature sensor was replaced by a software incompatible chip which
> resulted in much coarser temperature resolution. We don't know how that
> measurement was used in the control loop.

We do know that the temperature as reported by the DS1620 chip is used 
only to trim the OCXO frequency during holdover.  It plays *no* part in 
controlling the frequency during normal (GPS-controlled)  operation, nor 
during free-running operation (control loop off).

There is some discussion of this in the archive.

Best regards,

Charles