Trimble OCXO jitter - Page 1
Forum section: electronics / general

author: jadew
author_rank: Frequent Contributor
timestamp: March 25, 2014, 11:16:13 pm
content: Hello, I just got a Trimble 65256 OCXO (10 MHz), hoping that I could use it as a secondary frequency standard, so I don't have to keep my Rb running all day.Problem is it has a lot of jitter between every 2 cycles (the edges coincide perfectly each 2 cycles).I was wondering if anyone knows anything about this? Is it a common issue? Am I doing something wrong? Any chance of fixing it?The attached screenshots show how each cycle after the trigger varies.Thanks.Edit: Nevermind, I used a 50 Ohm termination and all it's fine now.

author: HighVoltage
author_rank: Super Contributor
timestamp: March 26, 2014, 10:16:27 am
content: Where did you get the Trimble 65256 OCXO and how much was it?

author: jadew
author_rank: Frequent Contributor
timestamp: March 26, 2014, 04:25:43 pm
content: Quote from: HighVoltage on March 26, 2014, 10:16:27 amGot it from ebay, it was $24, delivered.

author: rigrunner
author_rank: Frequent Contributor
timestamp: May 28, 2014, 08:19:41 pm
content: I don't suppose you got a datasheet or pinout with it?I've just acquired one with no information

author: Rufus
author_rank: Super Contributor
timestamp: May 28, 2014, 08:26:57 pm
content: Quote from: jadew on March 25, 2014, 11:16:13 pmIt sounds more like 5MHz amplitude modulation altering the trigger point. Did you try AC coupled input and/or trigger on the scope?

author: jadew
author_rank: Frequent Contributor
timestamp: May 28, 2014, 08:49:29 pm
content: @rigrunner: A quick google search turned this up:http://thumbs2.ebaystatic.com/d/l225/m/m7nQNXUOBrRbBYD1ywQbBaw.jpg@Rufus: I didn't try that, but even AC coupled, wouldn't have that simply reduced the jitter by half (at best)?

author: rigrunner
author_rank: Frequent Contributor
timestamp: May 28, 2014, 08:56:16 pm
content: I've come across a couple of different pinouts on google prior to posting.I was hoping for either a datasheet or "This is how i wired mine up and the smoke has stayed in"

author: jadew
author_rank: Frequent Contributor
timestamp: May 28, 2014, 09:10:06 pm
content: @rigrunner: The pinout in that picture is the same with what I had, however I noticed that other similar OCXOs, have different pinout, even tho the layout is the same.On the top left pin, where it says VL, you need to apply a voltage (don't know what the limits are) which will allow you to slightly adjust the frequency. I used a pot that I placed as close to the OCXO as possible so it gets heat up quickly.

author: Rufus
author_rank: Super Contributor
timestamp: May 28, 2014, 09:35:40 pm
content: Quote from: jadew on May 28, 2014, 08:49:29 pmI am suggesting there is no jitter on the signal it is just jitter in the scope trigger point because alternate cycles have different amplitudes.

author: rigrunner
author_rank: Frequent Contributor
timestamp: May 28, 2014, 10:05:06 pm
content: Quote from: jadew on May 28, 2014, 09:10:06 pmThanks. I'll power mine up tomorrow and see if it works.

author: jpb
author_rank: Super Contributor
timestamp: May 28, 2014, 10:19:49 pm
content: Quote from: Rufus on May 28, 2014, 09:35:40 pmI think the plots are different cycles on a single trigger i.e. he captured several wavelengths and then zoomed in on every odd one as can be seen from the value of D in nanosecs and the arrows pointing to where the trigger point is - but it is a bit academic as the OP states that using a 50 ohm termination has fixed it.

author: jadew
author_rank: Frequent Contributor
timestamp: May 28, 2014, 10:50:36 pm
content: Quote from: Rufus on May 28, 2014, 09:35:40 pmI understood that, my point was that even with the signal AC coupled, the scope would still see some jitter, due to the fact that the middle point would be an average across a big chunk of the signal and not on a per cycle basis, so each cycle's middle point would still be different than the signal's middle point, so the best case scenario would be 1/2 of the original jitter.Now, if it was indeed an amplitude issue, it's obvious to me that it wasn't symmetric, because I couldn't get a clean waveform no matter what trigger level I used, so for all intents and purposes, the jitter was real.As for the 50 Ohm termination, I'm still not sure if that's the correct value. This OCXO has clearly been designed to drive low impedance loads, but with out a datasheet it's hard to say what that value should be, especially since it's a custom oscillator and it seems to work fine with a wide range of impedances.Edit: I ran a little test and it turns out it was 5 MHz AM, just as you said, but AC coupling doesn't make any difference, just as I said