[time-nuts] [hp_agilent_equipment] Re: Upgrade an HP 5342A microwave frequency counter to have an oven oscillator.

[Bob Camp]

Hi

One clarification - there are multiple ways you can design an OCXO:

1) You can use an outer oven to improve the temperature stability under normal conditions.

2) You can use a second oven to “help” at the cold end of the  range (maybe below -20C)

3) You can simply do a really good single oven. 

Of the three, number 2 is pretty much useless unless you are outdoors in the winter. 

Number 3 works because oven design is a bit complicated. Gradients / gain balance / correct gain does all matter. 

Number 1 works when the gain and set points of both the inner and outer ovens are optimized for best performance. This is done by (possibly multiple) temperature runs and adjustments. To much or to little gain and performance degrades. Wrong set point on either oven and performance degrades. 

The 10811 “double oven” versions are #2 above. The later Z3815’s have an OCXO from category #3. A 260 or MV89 is an example of category #1.

Typically single ovens are doing well at 2x10^-9 over -30 to +70C. A reasonable double oven should be able to do < 2x10^-10 over -30 to +70C. Packing a whole bunch of insulation around a single oven may turn it from 2x10^-9 to 5x10^-9 over -30 to +70C. Optimizing one is not “trivial”.

Bob

> On Dec 2, 2014, at 4:53 AM, Dr. David Kirkby (Kirkby Microwave Ltd) <drkirkby at kirkbymicrowave.co.uk> wrote:
> 
> On 2 Dec 2014 03:10, "wb6dgn_tom at att.net[hp_agilent_equipment]" <
> hp_agilent_equipment at yahoogroups.com> wrote:
>> 
>> Isn't the 10811 a "double oven" oscillator (an oven within an oven)?  I
> also believe it has anticipator circuitry to predict changes based on
> environmental parameters.  Or...am I confusing this with another oscillator?
> 
> http://www.leapsecond.com/museum/10811a/10811a.pdf
> 
> Has a data sheet.  I believe that there are variants of the 10811A that are
> double oven, but not all are.
> 
> The fan is not blowing directly onto the oscillator,  as they are on
> opposite sides of the case. But they are both at the rear and given the
> instrument is only half the width of a 19" rack, maybe it is too close.
> 
> I have not checked this myself,  but someone said that the 5342A pre-dates
> the 10811A, so if purchased a 5342A new with the high stability
> oscillator,  one would get another oscillator with a poorer specification.
> 
> The  5342A/10811A combination is one of those things one would have to
> test, rather than guess. It would need some careful thought about how to do
> a worthwhile experiment.
> 
> Anyway, as far as I am concerned,  it is certainly worth while fitting the
> 10811A, as even without any equipment other than my eyes, I can see the
> last few digits are not constantly changing every second or so.  There's a
> dramatic improvement in short term stability.  I would guess it has  2-3
> orders of magnitude better short term stability, based just at looking at
> the display.  Actual measurements would quantify the improvement.
> 
> If I can get 100-1000x better performance,  for an upgrade that costs less
> than 25% of the instrument, that is worthwhile to me. Waiting 6 or so
> minutes to get a dramatic improvement in performance is not a big deal.
> Keeping it plugged in 24/7, for a bit more performance, is not worthwhile
> to me, but others may feel otherwise.
> 
> Dave.
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