Mark wrote:

Nothing it does in the first 6 hours has anything to do with
anything.  (1) The oscillator will be swinging around wildly
(comparatively speaking, relative to its stability after it has been
running unmolested for months).  (2) Further, 6 hours is almost
certainly a shorter period than it normally uses to forecast PU, so a
forecast after ANY six-hour period of data collection (even when
fully warm and stable) will not be its best estimate.

I do not know HP's algorithm, but it sounds like it didn't seriously
try to compute PU until after 6 hours, then it started trying with
(1) too little data and (2) data from an unstable oscillator, so it's
no surprise it is wandering around.  I'll be very surprised if it
settles down near its long-term stability in less than a month of
continuous, undisturbed running (continuous meaning don't turn it
off, undisturbed meaning don't move it or bump it very hard -- if you
do either of these, start counting from zero again).

Be patient.  OCXOs need time to reach stability when re-started in a
new environment (particularly if they have been off for more than a
few days and/or bumped around, both of which are probably true of
yours).  Some are better about this than others, but what I've said
is pretty typical of the 10811-and-better class of OCXOs, IME.

Best regards,

Charles

Thanks Guys, you have instilled a great deal of confidence in these "smartclocks" for me.

Anyone know where I can buy a month's supply of patience then? ;)

On a more serious note, I have rack mounted both clocks with UPS power and they shall not be disturbed.
http://www.vk2hmc.net/blog/?p=86

Many thanks,
mark

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Charles P. Steinmetz
Sent: Wednesday, 17 April 2013 4:03 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Z3805A high value PU

Mark wrote:

Nothing it does in the first 6 hours has anything to do with anything.  (1) The oscillator will be swinging around wildly (comparatively speaking, relative to its stability after it has been running unmolested for months).  (2) Further, 6 hours is almost certainly a shorter period than it normally uses to forecast PU, so a forecast after ANY six-hour period of data collection (even when fully warm and stable) will not be its best estimate.

I do not know HP's algorithm, but it sounds like it didn't seriously try to compute PU until after 6 hours, then it started trying with
(1) too little data and (2) data from an unstable oscillator, so it's no surprise it is wandering around.  I'll be very surprised if it settles down near its long-term stability in less than a month of continuous, undisturbed running (continuous meaning don't turn it off, undisturbed meaning don't move it or bump it very hard -- if you do either of these, start counting from zero again).

Be patient.  OCXOs need time to reach stability when re-started in a new environment (particularly if they have been off for more than a few days and/or bumped around, both of which are probably true of yours).  Some are better about this than others, but what I've said is pretty typical of the 10811-and-better class of OCXOs, IME.

Best regards,

Charles

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On Wed, 17 Apr 2013 08:26:08 +0000, Mark C. Stephens wrote:

Is it wise to install an unregulated fan inside the 3805 housing , so
close to the OCXO ?

I'd have thought the OCXO would like it "Nice and warm" with out thermic
disturbances.

But the i'm just a t'nut beginner
CFO - Denmark

Hi CFO,

I am normally pretty quiet on the group but I have been lurking and learning for the last 5 or so years.
There is an amazing amount of information passed around the timenuts group to depths I often can't fathom.
The knowledge gap between me and some of the people here is just plain scary!

The 2 Z3805A I received have definitely been force air cooled, the way the dust built up on them suggests a constant flow of air across them.
They could have been mounted vertically, the air being sucked out from the top (right on the horizontal).
It would be interesting to know what the 'rack' that they came out of looked like and the cooling arrangement.

I am kind of hoping the Double oven can take care of itself, and the fan will keep the PSU board nice and cool.
I didn't drill holes in the chassis in case we deem it necessary to remove the fan(s) later on.

The fans are proper 48v blowers running off 24V.
When I removed the power switch, I took the input to the PSU board straight to the cannon connector on the back.
I have some young kids that love to play with switches, something I really want to avoid with my GPSDO ;)
I also took 2 more wires out of the Cannon connector (+ & - 24v) to a flying lead socket to plug the fan in.

I have kept all the bits safe so I can restore it to the original condition I received it in, just in case :)

mark

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of cfo
Sent: Thursday, 18 April 2013 4:32 AM
To: time-nuts@febo.com
Subject: Re: [time-nuts] Z3805A high value PU

On Wed, 17 Apr 2013 08:26:08 +0000, Mark C. Stephens wrote:

Is it wise to install an unregulated fan inside the 3805 housing , so close to the OCXO ?

I'd have thought the OCXO would like it "Nice and warm" with out thermic disturbances.

But the i'm just a t'nut beginner
CFO - Denmark

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