It's hard to be sure without knowing the characteristics of the DAC ouput and the oscillator EFC, but if you're only making a one off I wonder if it might perhaps be possible to simplify that arrangement to just a potential divider using selected values and being fed from the DAC and tapped off into the EFC? Regards Nigel GM8PZR In a message dated 31/01/2014 18:04:39 GMT Standard Time, [email protected] writes:
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 <[email protected]> >To: Bob Stewart <[email protected]>; Discussion of precise time and frequency measurement <[email protected]> >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 <[email protected]> >>To: Discussion of precise time and frequency measurement <[email protected]> >>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 -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
