Vectron OCXO teardown - Page 1
Forum section: electronics / rf-microwave

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 12, 2024, 12:25:31 pm
content: I just got two Vectron C4550 10MHz OCXOs with a supposed SC-cut crystal inside. I bought them from ebay for $12 - of course they are not new.Their package was quite dented. I know people who scavenge old PCBs are not of the super cautious kind but why do they harm the stuff they wanna sell?One of the oscillators works and seems to be rock stable compared to another OCXO. It´s very fascinating to see two free running oscillators have very little phase shift on the scope.The other was dead on arrival - so I couldn't resist taking the Dremel and to invest two cutting wheels to have a look inside. For whoever wants to know what´s inside too, here are the pictures! And if anyone should see any hints if this special oscillator is really SC-cut or just of the usual AT-orientation then please let me know...EDIT: I just don't know if the broken crystal disc was the reason that the oscillator did not start. It may have split during the teardown, but I handled the part quite carefully. I suppose it was broken before.

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 13, 2024, 04:21:46 pm
content: Update: The OCXO seems to be of the SC-cut type.AT-crystals usually have a higher frequency at lower temperature, so that after power on the frequency falls until it stabilizes at 10MHz.This part starts around 9.999970MHz and rises up to 10MHz. AFAIK this is typical for SC-crystals.

author: 5U4GB
author_rank: Super Contributor
timestamp: October 14, 2024, 05:18:46 am
content: Vectron? You mean?

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 14, 2024, 06:54:20 am
content: Link is broken...

author: 5U4GB
author_rank: Super Contributor
timestamp: October 14, 2024, 07:54:40 am
content: Quote from: Phil1977 on October 14, 2024, 06:54:20 amSorry, edit fail, now corrected.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 14, 2024, 09:14:29 am
content: Quote from: Phil1977 on October 13, 2024, 04:21:46 pmThe change in frequency is only 3 ppm. The normal AT crystals can have a positive or negative TC - especially with the low quality ones it can be all over the place. The AT crysals have a wider range with low TC, while the SC cut ones are better near 45° C, but get worse when further off.That the frequency is going up with temperature is at least compatible with an SC cut.From the pictures it is hard to tell - the difference is just a slightly different orientation of the crystal lattice.

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 14, 2024, 10:01:12 am
content: Quote from: Kleinstein on October 14, 2024, 09:14:29 amUnfortunately my X-ray diffractometer is not available right now ;-)I thought maybe there are differences in the driver circuit. It was mentioned in a comparison that you need narrower frequency filters for SC-cut crystals because else they may oscillate in a wrong mode.Compared to the CTI-oscillators the onset behaviour is definitely different - the CTIs start around 100Hz over 10MHz and go down, the Vectron and one ISOTEMP OCXO that I could test start 20-30Hz below 10MHz and go up.My current goal is to have three oscillators - one of them is a GPSDO - and make a continuous phase measurement between all of them. I hope that this "triumvirate" allows to identify which oscillator is drifting without comparing to a rubidium standard.

author: tchicago
author_rank: Regular Contributor
timestamp: October 15, 2024, 07:51:48 pm
content: These small metal-case OCXOs don't have any thermal insulation inside. Which means their temperature will be affected by changing environmental conditions, like a nearby fan turning on, etc. The temperature stabilization circuitry will surely take care of that, but not immediately, which will lead to frequency fluctuations. Are you expected to put the whole thing into a some thermally insulated enclosure?Also, if it maintains the temperature of, say 70C and has no thermal insulation inside, this means the case will be hot and will emit heat and will consume extra power to maintain that temperature. I have one of these from the other Chinese manufacturer, and it gets so damn hot to touch when it reaches its working temperature. This is the teardown of the same type that I have:

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 16, 2024, 07:20:47 pm
content: Yep, as already mentioned in another thread I want to put the OCXO into a thermally insulated housing to keep the power consumption down. It will be part of a portable timestamp generator for offline measurements, and an accuracy of <1ms per day is required, <0.01ms would be ideal. (Should be doable - 1day are slightly less than 10^5 seconds. 1ms deviation refers to 10^-8 frequency accuracy.)