Tim,
The shape does not look exactly what I would expect from a less than
critical damped oven, it looks a little to peaky, but maybe it is the
resolution of the graph that fools my eye.
Agree that you end up in critical damped oven with fast warmup requirement.
Cheers,
Magnus
On 10/02/2014 02:41 PM, Tim Shoppa wrote:
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) <
[email protected]> wrote:
On 2 Oct 2014 07:10, "Magnus Danielson" <[email protected]>
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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