EEVblog #647 - Agilent 53131A Frequency Counter Oven Upgrade

[EEVblog]

What I have found using the Trimble OCXO's is that you need to wait only 10 minutes to get 99.9% of the way there, its not that bad at all really. I would honestly say its worth it, without a doubt its worth it, all of my counters now have OCXO's in them, once you know the extreme difference between an ovenized OCXO and a non-ovenized one you would not go back I am sure

Yes, I think my oven settles down to better than the built in non-oven xtal pretty darn quick, so a worthwhile upgrade for sure.

[SeanB]

I ovenised this crystal in a function generator about 25 years ago. Simple heater using a bipolar transistor with the Vbe drop switching it as it reaches a setpoint. Depends on the 5V supply feeding the base being stable, but it does work quite well. Transistor is soldered to the crystal case to improve heat transfer, ad the cardboard provides thermal isolation. Works well, though you can see the drift as it warms up if you feed a signal in, but it stays stable ( or at least as much as the Intersil chip will stay stable) when warm. No idea of long term stability, as I no longer have access to a precision frequency source, but it was a lot better than leaving it to drift with room temperature..

[David Hess]

They used to make little temperature stabilizing ovens that fit over TO-99 packaged operational amplifiers that used something like a positive temperature coefficient thermistor element to regulate the temperature.

[plesa]

The one thing that puts me off "upgrading" my Freq Counter to an OCXO is the necessary "wait" after power on.  I can think of loads of times i just want a quick single measurement, and unfortunately i haven't got the shelf/bench space to leave the thing out and switched on the whole time.
 Could you measure the "accuracy" vs time after switch on?  Even if you just write a few numbers on a piece of paper say every 30secs?  Be interesting to see how long you need to wait to get a better result that the build in oscillator??

What I have found using the Trimble OCXO's is that you need to wait only 10 minutes to get 99.9% of the way there, its not that bad at all really. I would honestly say its worth it, without a doubt its worth it, all of my counters now have OCXO's in them, once you know the extreme difference between an ovenized OCXO and a non-ovenized one you would not go back I am sure

Gerry

Based on my measurement there is big difference in lock time between double oven OCXO and single oven.
As double oven I used C-TEC 2055B the "lock in" time is about 11,5 min. Allan deviation about 100uHz (30min warm up)
Single oven IsoTemp 131-191 is ready in 40s, but Allan deviation is about 3x worse than the double oven OCXO.
Rubidium FE5680A is locked in about 2,5 min, but 3 times higher power consumption compared to double oven oscillator.

The best compromise is the double oven OCXO I suppose.

Measured with Agilent 53230A with genuine OCXO. I do not know the type of OCXO inside (no teardown yet).

Fora details about various OCXO you can check
http://www.meinbergglobal.com/english/specs/gpsopt.htm

[Macbeth]

Dave, have you checked out Shahriar's 3GHz Channel 3 upgrade vid?
That also looks to be a really cheap aftermarket upgrade well worth doing on the 53131A!

I'm going to keep my eyes peeled, but expect the ebay prices of 53131A's will have lifted a bit since both your and Signal Paths vids 

[HighVoltage]

I have the 53131A with Option "010 HS Oven"
Your video made me curious of how the original implementation was done with the oven crystal.
So I just opened it up and took some pictures.

Interestingly, it seems this one has two potentiometers for adjustment / calibration.
One at the back in the same position as the unit without the oven and one adjustment directly on the oven crystal.
 

[HighVoltage]

I wonder, why are there 2 Osc. Adjustments on this counter?

[edpalmer42]

The HP 10811 oscillator is a high-performance single oven SC oscillator that's used in many pieces of HP equipment.  Aging is spec'ed at 5e-10 per day.

The frequency adjustment on the oscillator is a coarse adjustment via a variable capacitor.  The range is +-1 ppm over 18 turns.  The potentiometer varies the DC level to the EFC (Electronic Frequency Control) lead.  The range is +-0.1 ppm for voltages of -5 V to +5 V.

There was a double-oven version of the 10811 that shows up for sale occasionally.  Unfortunately, the controller for the outer oven is on a different board so you'ld have to roll your own.

Ed

[HighVoltage]

Thank you Ed for this explanation.
There are a lot of these HP Oscillators on ebay for pretty high prices,
It seems like the option that Dave choose was much cheaper.

[Dave]

At 7:20, when you speak about short-term stability: The Morion datasheet shows Allan deviation figures, while the CSIRO rubidium datasheet shows Allan variance. According to the Wikipedia article, ADEV² = AVAR, so the figures from the two datasheets are not directly comparable.
But then again, if we do the calculation, the Allan variance (at 1s) of the Morion OCXO would be <4*10^-24, which just doesn't sound right, compared to the Allan variance of the CSIRO RbXO (<2*10^-11). Can we assume that they screwed up the Morion datasheet and they actually meant to write Allan variance?

Would anyone knowledgeable in the field be willing to comment on this?

[JonnyBoats]

Dave,

Not sure if this is the right section of the forum for this question but here goes anyway:

Obviously the 53131A is a keeper and not just fodder for teardown Tuesday else you would not be upgrading it. Do you plan on doing more upgrades like the prescaler and perhaps interfacing the GPIB to your computer?

[Ronald1962]

Hi Dave (or anybody else here),

Could you please tell me why / for what purposes this accuracy is needed?

I'm just a rooky so that I think now, my counter is just garbage because it has not this accuracy.

Regards

Ronald

[EEVblog]

Obviously the 53131A is a keeper and not just fodder for teardown Tuesday else you would not be upgrading it. Do you plan on doing more upgrades like the prescaler and perhaps interfacing the GPIB to your computer?

I'll probably get a prescaler kit for it.
And yes, I need a USB GPIB interface. I thought I had one somewhere but I can't find it 

[aggie72]

Dave,

I've watched more EEVB videos than I can count and finally decided to join EEVBlog and this is my first post.  Anyway watching this video I was wondering why you didn't use the X-Y mode of the oscilloscope to get a lissajous display.  For me it's so much easier to adjust oscillators this way using a reference.  Any way keep up the good work, I really enjoy the blog 

[Macbeth]

Dave,

I've watched more EEVB videos than I can count and finally decided to join EEVBlog and this is my first post.  Anyway watching this video I was wondering why you didn't use the X-Y mode of the oscilloscope to get a lissajous display.  For me it's so much easier to adjust oscillators this way using a reference.  Any way keep up the good work, I really enjoy the blog 

And with a good old analogue scope too! Can't beat XYZ on a CRO!

[edpalmer42]

Dave,

I've watched more EEVB videos than I can count and finally decided to join EEVBlog and this is my first post.  Anyway watching this video I was wondering why you didn't use the X-Y mode of the oscilloscope to get a lissajous display.  For me it's so much easier to adjust oscillators this way using a reference.  Any way keep up the good work, I really enjoy the blog 

I've tried that, but I don't like it.  It's too hard to see slow phase changes.  I prefer to overlap the two sine waves and make a note of where the two signals cross each other.  It's very easy to see if those points move, even if it takes 5 minutes.

Ed