The problem is certainly real enough. What you're seeing is a drift of approx 2500ppm, and Vishay shows the temperature coefficient of their standard carbon film resistor, for example, to be approx 200ppm per degree C for a value of 20K. If yours is carbon film this would imply your measured resistor is seeing a temperature rise of around 10 or 12 degrees C, which might be a bit on the high side but is certainly feasible given a body temperature of around 35 degrees C. Standard metal film resistors have a lower temperature coefficient, say around 50ppm per degree C, so this might be one option for reducing the effect, another could be temperature control of your EFC network. There are more specialised resistors with much lower temeparature coefficients, the Vishay RCME series of metal film resistors for example can be as low as 5 to 6 ppm per degree C, although I don't know what the cost difference might be. And no, I don't have any shares in Vishay:-) Regards Nigel GM8PZR In a message dated 31/01/2014 17:04:24 GMT Standard Time, b...@evoria.net writes:
I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth of holding it between fingers moves it by about 50 ohms. What type of resistors should I put in there? Or am I chasing a problem that doesn't exist? Totally out of my league here. Bob - AE6RV _______________________________________________ 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. _______________________________________________ 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.
