Jellybean resistors can have a tempco in the 100s of PPM per degree C. Some precision resistors are as low as 25 PPM/C while really good resistors can be had at 5 PPM/C. Better yet look for a resistor array where part tracking is called out. Some arrays get below 5 PPM tracking so the division ratio holds much better than the absolute value. (I find the DigiKey part search tool helpful in finding the low PPM parts I want.)
Another possibility is an integrated resistive divider like the Maxim MAX549x series. The have pre-trimmed dividers in a number of ratios and values, typically with 35 PPM/C absolute tempcos but ratiotempcos as low as 2 PPM/C. Bob LaJeunesse >________________________________ > From: Bob Stewart <b...@evoria.net> >To: Discussion of precise time and frequency measurement <time-nuts@febo.com> >Sent: Friday, January 31, 2014 12:01 PM >Subject: [time-nuts] EFC divider resistors > > >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.
