10 Mhz OCXO standard - Page 1
Forum section: electronics / beginners

author: M0BSW
author_rank: Frequent Contributor
timestamp: December 09, 2013, 10:13:09 am
content: Hello Everyone,What I've made a start on building is a 10 Mhz square wave frequency standard, which is something I've been itching to build for quite a while, and I'm sure you will know is very useful device in my radio shack.I do have a couple of questions regarding this project, you may I hope like to ponder over and hopefully give some advice on.1/ The ocxo is in a can, to I need to also mount it to a heat sink, or are they ok with out!!!.2/ I want to have 4 bnc outputs, so would it be advisable to make 4 buffer outputs one for each output, I'm not following any particular circuits. so "anyone ever built one". Always any of your help would be appreciated.PaulM0BSW UK Radio Amateur

author: peter.mitchell
author_rank: Super Contributor
timestamp: December 09, 2013, 11:07:40 am
content: http://gerrysweeney.com/build-a-10mhz-rubidium-frequency-standard-and-signal-distribution-amp-for-my-lab/this might help

author: KJDS
author_rank: Super Contributor
timestamp: December 09, 2013, 11:14:07 am
content: There is no need to try and cool an OCXO, the internal oven is designed to heat up and the less heat you drag away from it the better. Just make sure that the ambient doesn't get too near the oven temperature.

author: peter.mitchell
author_rank: Super Contributor
timestamp: December 09, 2013, 12:20:18 pm
content: I linked that mainly for the amp/buffer bit, the amp chip is EOL, but can still be found aroundhttp://octopart.com/partsearch#!?q=CLC409

author: M0BSW
author_rank: Frequent Contributor
timestamp: December 09, 2013, 04:12:28 pm
content: Thanks Peter

author: Matje
author_rank: Regular Contributor
timestamp: December 09, 2013, 11:57:45 pm
content: Quote from: M0BSW on December 09, 2013, 10:13:09 amThink about the square wave part again. Usually frequency standards use sine waves, because these have way less harmonics and are much easier to distribute. Most test equipment takes sine waves as reference inputs AFAIK.Lots of harmonics are a very bad thing in a radio shack I think.Quote from: M0BSW on December 09, 2013, 10:13:09 amNo heatsink needed, nor would it be a good idea.Quote from: M0BSW on December 09, 2013, 10:13:09 amThe keyword would be buffer amplifier or distribution amplifier.Think about and check what signal level you'll usually need, I think something like +7 to +10 dBm sine wave into 50 ohms is quite common.Also think about whether you want electrically isolated (floating) outputs. I personally feel these are very nice to have - but it's more effort/costs of course.

author: G0HZU
author_rank: Super Contributor
timestamp: December 10, 2013, 12:14:42 am
content: One thing I would advise (if you want to preserve accuracy and stability of a good OCXO) is that you buffer the output well before you then fan it out to 4 outputs. This is to prevent short term load pulling of the OCXO each time you connect something to one of the outputs.I wouldn't worry too much about using a 10MHz square wave as my 10MHz OCXO (in a box) has a square wave output and this makes it compatible as an external reference for various counters or signal generators I have here.You can always filter the square wave to a sine wave for some of your outputs anyway?A lot depends on what accuracy you want or expect from it. Don't get too drawn into trying for fabulous stability or accuracy because there is little point in having this. I'm happy if my 10MHz OCXO is within 0.2Hz of 10MHz over several months of ageing. Usually it's better than this but I have resisted going for Rubidium or GPS locked standards. I did design and build a 10MHz (locked to 198kHz) offair standard many years ago and I use this to check all my various 10MHz references and keep them within 0.2Hz at 10MHz

author: M0BSW
author_rank: Frequent Contributor
timestamp: December 10, 2013, 07:22:31 am
content: Quote from: G0HZU on December 10, 2013, 12:14:42 amThank you , I just want it for referencing , and for the experience of building one, because I'm at a stage where I can, I have emailed Gerry Sweeney, who has had a lot of experience with these, and has given me some valuable advice on the OCXO and in particular the one I've bought, plus how to make it go to sine wave by the use of a 10Mhz filter, re amplifying the signal in the buffer stage, so I could I guess have two sine wave and two square wave outputs.Paul