Frequency stability of an HP3310A function generator - Page 1
Forum section: electronics / testgear

author: KJDS
author_rank: Super Contributor
timestamp: February 04, 2015, 05:26:19 pm
content: I've just been asked what the stability is like for an old analogue HP3310A function generator that I've sold so thought I'd run some tests this evening.I let it warm up, set it to 100kHz and it measured 100.454kHz.I'll keep the thread updated to report how it drifts.

author: KJDS
author_rank: Super Contributor
timestamp: February 04, 2015, 06:11:13 pm
content: It's now at 100.366kHz

author: Yago
author_rank: Frequent Contributor
timestamp: February 04, 2015, 06:36:45 pm
content: How are you measuring it?Just guessing here, but interested, I imagine a counter would have drift too.

author: KJDS
author_rank: Super Contributor
timestamp: February 04, 2015, 06:42:22 pm
content: Quote from: Yago on February 04, 2015, 06:36:45 pmI'm using a Keithley 2015THD, which has a not very accurate frequency reference, but it's likely to be way better than the HP3310A.It's now at 100.365kHz and I'm off to find a better counter as I've just seen that the ancient HP box is far more stable than expected.

author: Yago
author_rank: Frequent Contributor
timestamp: February 04, 2015, 06:51:06 pm
content: Oh to even have the choice!

author: KJDS
author_rank: Super Contributor
timestamp: February 04, 2015, 07:31:36 pm
content: It's now reading 100.360 on the Keithley and 100.359 on a HP5334B

author: Yago
author_rank: Frequent Contributor
timestamp: February 04, 2015, 08:10:01 pm
content: That's just showing off now Kev

author: KJDS
author_rank: Super Contributor
timestamp: February 04, 2015, 08:27:24 pm
content: They've both settled down to 100.355kHzGiven that the Keithley freq spec is only 0.01% and its not been calibrated in years it's doing well

author: KJDS
author_rank: Super Contributor
timestamp: February 04, 2015, 09:17:54 pm
content: 100.349I'm amazed at just how stable this is

author: Yago
author_rank: Frequent Contributor
timestamp: February 04, 2015, 10:17:05 pm
content: Tell you what, it's better than formula 1 this!

author: KJDS
author_rank: Super Contributor
timestamp: February 04, 2015, 11:03:42 pm
content: 100.352Time for bed, so that's all folks.

author: Yago
author_rank: Frequent Contributor
timestamp: February 04, 2015, 11:13:40 pm
content: Cya later KJDS.If you get time tomorrow, could you explain what we should look for when evaluating a gen like this?What might be obvious, may not be so to the likes of me!Cheers

author: Unknown
author_rank: Unknown
timestamp: February 08, 2015, 12:37:03 am
content: Quote from: KJDS on February 04, 2015, 06:42:22 pmI have a HP 3312A that is very _un_stable in frequency. Frequency drops about 20% over the course of two hours (even after warming up before starting), and doesn't really settle down even after 6 hours. I wish I knew where to start looking for the problem...

author: Paul Moir
author_rank: Frequent Contributor
timestamp: February 08, 2015, 02:21:40 am
content: The 3312A just has a simple VCO controlling it's frequency. Have a look at figure 7-5 in the manual, bottom or left hand side depending on which way you're looking at it. Either it's one of the power supplies drifting (17, 14 and -14), the VCO input, something coming in from the modulation generator or one of the half-dozen components that make up the VCO.Let me know if there's any specific measurements you want made.