); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY In a message dated 11/7/2007 13:07:32 Pacific Standard Time, [EMAIL PROTECTED] writes:
>After that, oven current is relatively constant by comparison. >In a GPSDO the EFC is part of a closed loop. So even if there >is a small voltage offset in the EFC control or return path due to >heater current, it seems to me that it still has no effect on either >the accuracy or the stability of the GPSDO. So we ignore that >case too. >Is the worry, then, about the minor ambient temperature related >variations in steady-state oven current? Or something else? Hi Tom, yes, the ambient temperature variations will cause a significant heater current change, especially if they are very fast due to AC kicking-on etc. Current changes for a typical Euro-can size OCXO can vary from 0.09A to 0.16A due to these thermal changes in an ambient environment (lab bench). If the heater is exposed to the outdoors, this can be even worse. Any voltage induced into the EFC ground return due to these current changes can reduce the short term stability of the OCXO and cause phase drift. It's one more error source in the system. We see only typically 5 to 10 microvolt variations in the EFC voltage due to diurnal temperature changes (aging offset removed) on the best double oven OCXO's we have seen mounted onto Fury. Putting the OCXO on a long cable and having the current go from 90mA to 160mA can produce much more than 10 microvolts in EFC error, so the system's accuracy is reduced due to this. bye, Said ************************************** See what's new at http://www.aol.com _______________________________________________ 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.