I probably should have called it more correctly frequency control. Thanks to the help from Scott N5TNL we clearly where able to watch the DDS as fan cooling was added and removed from the Rb. Only a small change resulted in the DDS tuning word changing by 89 which is a frequency change of 6 e-11. The source has to be a temperature sensing element feeding one input to the 4 channel 12 bit ADC. Some one please work this issue identify and disable that sensor and run a test verifying that tuning is not lost. Thank you Bert Kehren _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.