[time-nuts] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on

Tim Shoppa tshoppa at gmail.com
Thu Oct 2 08:41:57 EDT 2014


The overshoot behavior from 150 to 220 seconds is exactly what you expect
for slightly less than critical damping which is where many closed loops
end up when rapid lock or warmup is a criteria. Most rapid warmup is almost
always the design point of an OCXO oven.

Tim N3QE

On Thu, Oct 2, 2014 at 3:21 AM, Dr. David Kirkby (Kirkby Microwave Ltd) <
drkirkby at kirkbymicrowave.co.uk> wrote:

> On 2 Oct 2014 07:10, "Magnus Danielson" <magnus at rubidium.dyndns.org>
> wrote:
> >
> > David,
> >
> > The character of starting high/low and then stabilize some 5-30 min later
> is typical of oven oscillators. Underdamped ovens have been seen before, I
> have even seen one on the brink of oscillation.
>
> Thank you. Do you know the likely cause of the somewhat odd behaviour
> between about 150 and 220 s?
>
> This eBay auction,  which someone posted
>
> http://m.ebay.com/itm/151256172424
>
> says it's the high stability oscillator for an HP 8753D or 8753ES. I
> checked the part number at parts.keysight.comand it would appear it is the
> same as used in my VNA and several other microwave VNAs.
>
> That said,  I have noticed a few errors on parts.agilent.com, one of which
> resulted in me buying the wrong part. I was later warned by Agilent not to
> trust the accuracy too much, especially on older equipment. It is better to
> check with them before making purchases.
>
> But they have a very helpful parts service that does make every effort to
> sort out what parts are. They spent quite some time finding out what
> connectors were on am obsolete cable for me.
>
> > TCXO will not have the same wide range, as it compensate for the
> temperature.
>
> This answers my original curiosity now - did I have an OCXO  or TCXO.
>
> Although I am not going to bother, as it will be easier and more accurate
> to feed the VNA from a rubidium or GPS locked TCXO/OCXO, it would probably
> be possible to buy one of those off of eBay and replace the OCXO with a
> better one. Then stick it in my VNA - I would not want to modify the
> original one.
>
> There have some rather small double oven OCXOs on eBay recently for very
> little money.  From the earlier comments about this oscillator, it would
> appear its specification is quite poor for an OCXO.
>
> > Cheers,
> > Magnus
>
> Thank you.
>
> Dave
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