I just realized that I have a pot in the mix. I see one on Mouser with 25PPM/C, so I suppose I'll try that. Here's the circuit I'll use with the replacements. What I have in there now has the values of R3, R4, and R5 multiplied by 10 and R2 is 3.9K. I suppose it won't matter so much for the pot.
http://www.evoria.net/AE6RV/GPSstd_PLL/EFC%20Divider/EFC2.png Bob >________________________________ > From: Robert LaJeunesse <rlajeune...@sbcglobal.net> >To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency >measurement <time-nuts@febo.com> >Sent: Friday, January 31, 2014 11:40 AM >Subject: Re: [time-nuts] EFC divider resistors > > > >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.
