# Selecting an OXCO 10Mhz ref

#### Mikebits

##### Well-Known Member
I recognize the Trimble brand, very well known for high quality standards, although those pictures look like the units are very old. I would stick with sine wave output @ 0 dBm. Most of the test gear will couple the ext ref into a divider chain anyways. If you have a strong 10MHz squarewave running around your lab you will have harmonics every 10 MHz, and this will cause you headaches.

Jim B. Is the resident radio guy, so he may suggest otherwise.

#### JimB

##### Super Moderator
If you have a strong 10MHz squarewave running around your lab you will have harmonics every 10 MHz, and this will cause you headaches.
Should be OK if you use decent coax cable and connectors to connect it all together.
If it is a 50/50 square wave, there should only be odd harmonics any way.

Jim B. Is the resident radio guy, so he may suggest otherwise.
Thank you for the compliment, but please don't over estimate my abilities!

JimB

#### Tony Stewart

##### Well-Known Member
THe VNA will need low phase noise which you get from all SC cut crystals which are more than 100x better than common AT cut crystals. (higher Q)

They must be ovenized and double ovens can improve regulation in a smaller can. They will all run from 5V and sine out.

The Vectron ones will be around 1e-10 frequency stability.

I used them in the mid-70's and were stable to 1e-11 and ruggedized for 1e-10 over all environmental stresses and worth $450 40 years ago and they haven't got any cheaper.(new) Last edited: #### Mosaic ##### Well-Known Member I ordered a$16 Trimble 65256, 10Mhz sine wav, 12V OCXO from Ebay to try out as the risk seems low. It has the output level > 0 dBm that the Rigol DSA wants and I note Trimbles have very good Phase noise. .
I may have to make a low phase noise buffer amp (transistor is probably best) to feed the Rigol and the VNA etc at the same time. I don't think I want to use the RIGOL 10Mhz output for the VNA sync...due to added phase noise.
Also I'll make a custom linear PSU for it based around this approach:
http://www.wenzel.com/documents/finesse.html

Some PSU noise /GPS info:
http://www.leapsecond.com/pages/tbolt/noise.htm

Buffer distributiion amp.
http://home.teleport.com/~oldaker/buffer_amp.htm

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#### Tony Stewart

##### Well-Known Member
I have no idea what the requirements for your equipment are. They ought to be available.
1. Frequency Stability vs time, temp and supply
2. Phase Noise vs f

Then you can decide if your selection is ok.
Does it matter if you have two different instruments with separate 10MHz unsynchronized sources.

#### Mikebits

##### Well-Known Member
His network analyzer just needs 10MHz sine wave input at 0 dBm. Don't know about the Rigol.

#### Tony Stewart

##### Well-Known Member
0 dBm is the minimum, <1e-9 stability is offered with optional internal OCXO, Accuracy affects lowest f input as LO and 1st of 3 IF are above highest input f in GHz.

E.g. 0.1 ppm error at 5GHz is 500 Hz on results which is only significant on measurements below 5kHz

1e-9 error could be something like 5 Hz error .

It often takes 30 minutes for OCXO to stabilize after power on to 1e-8 and longer for 1e-10 which is possible after calibration for Time of day or Doppler applications on SC cut OCXO's since they have exceptionally high Q and null temperature curve near 65 (est)'C used for oven control point.

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#### throbscottle

##### Well-Known Member
I know this thread is old, but...
I just ordered one of these Trimble 65256 OCXO's from eBay. Trying to find out any info on them, some people are saying they are double ovened. Does anyone know if this is true?

I've got it for making a GPSDO, btw so I can buy flakey cheap old equipment and calibrate it...

#### Mosaic

##### Well-Known Member
I don't believe it is double. It seems too small.
I also have a rubidium clock in cal to fire up when I get time to calibrate the OXCO

#### throbscottle

##### Well-Known Member
And I can dream of such things...

#### throbscottle

##### Well-Known Member
Wow, you did well there. I've only seen the older, big ones listed over here. I stopped looking once I discovered they have to be calibrated and the rubidium modules can wear out. GPS is very attractive because calibration isn't an issue. Just the massive jitter to contend with...

#### Mosaic

##### Well-Known Member
I got an Sa.22C dated July 2k8 calibrated in 2011 to
<±5x10E-11