HP 5370B low frequency modulation
Hi fellow time-nuts,
As I was going to make a casual measurement of the HP 5370B 10 MHz output, i.e.
that of its HP 10811-60111 OCXO, I came to see an unexpected modulation. It has
a slow modulation frequency modulation of about 5,2 mHz or there abouts. Quite
digital/squarewave-like I might add. Not actually squarewave, but rather some
form of PWM signal. Another interesting aspect was that it had a fairly steady
high, abrupt fall down a slight recovery, a jump upwards and then fall up to
the steady high level. The high frequency was the longer part of the time.
The cycle-time of these are low, for the 200 5 sec samples I took, I had about
10 cycles or so. So it is about two minutes cycles. The rate varied greatly.
I have not seen any specific details in the HP 5370B service manual about where
the HP 10811-60111 EFC is hooked up to anything, but I have noticed that more
or less everything is grounded on the connector. Now, if there is low-frequency
modulations of any large current there, it may kreep in. But it seems a bit
high for that.
I used both a Pendelum CNT-90 as well as a HP 5372A to measure this. I used
both the Cs and Rb as reference and it made no difference. The CNT-90 between
the two showed only noise, so this quick and dirty three-cornered hat certainly
pointed its crookied finger at the HP 5370B. The HP 5372A was using its own
well heated 10811-60111 as reference but that told the same story.
I might add that the 5370B was running in "cabed" condition, i.e. top and
bottom lids where off as well as the right side. The top lid needs to be off if
you want to have a chance of trimming it. The 5370B has been in bypass 9 days,
so I consider the 10811 fairly heated.
Has anyone else seen this? Tom?
Cheers,
Magnus
Magnus Danielson wrote:
Hi fellow time-nuts,
As I was going to make a casual measurement of the HP 5370B 10 MHz output, i.e.
that of its HP 10811-60111 OCXO, I came to see an unexpected modulation. It has
a slow modulation frequency modulation of about 5,2 mHz or there abouts. Quite
digital/squarewave-like I might add. Not actually squarewave, but rather some
form of PWM signal. Another interesting aspect was that it had a fairly steady
high, abrupt fall down a slight recovery, a jump upwards and then fall up to
the steady high level. The high frequency was the longer part of the time.
The cycle-time of these are low, for the 200 5 sec samples I took, I had about
10 cycles or so. So it is about two minutes cycles. The rate varied greatly.
I have not seen any specific details in the HP 5370B service manual about where
the HP 10811-60111 EFC is hooked up to anything, but I have noticed that more
or less everything is grounded on the connector. Now, if there is low-frequency
modulations of any large current there, it may kreep in. But it seems a bit
high for that.
I used both a Pendelum CNT-90 as well as a HP 5372A to measure this. I used
both the Cs and Rb as reference and it made no difference. The CNT-90 between
the two showed only noise, so this quick and dirty three-cornered hat certainly
pointed its crookied finger at the HP 5370B. The HP 5372A was using its own
well heated 10811-60111 as reference but that told the same story.
I might add that the 5370B was running in "cabed" condition, i.e. top and
bottom lids where off as well as the right side. The top lid needs to be off if
you want to have a chance of trimming it. The 5370B has been in bypass 9 days,
so I consider the 10811 fairly heated.
Has anyone else seen this? Tom?
Cheers,
Magnus
Hej Magnus
Oscillation/cycling of oven temperature?
Oven controller oscillation?
Bruce
From: Dr Bruce Griffiths bruce.griffiths@xtra.co.nz
Subject: Re: [time-nuts] HP 5370B low frequency modulation
Date: Mon, 23 Jul 2007 11:14:25 +1200
Message-ID: 46A3E4D1.2000900@xtra.co.nz
Hej Magnus
Hej Bruce,
Oscillation/cycling of oven temperature?
Oven controller oscillation?
Might be, but then my "loadingcondition" has caused the oven control out of
stability. This would certainly supprice me. The oven control in the 10811 is
linear and for most practical purposes behave like a first-degree linear
diffrential system. OK, there might be a second degree aspect, but the poles
should be fairly stable and it would be more a pure "amplitude" problem.
Now as I was down putting the hood on (and removing some of the residues from
the not so very smart packaging, using isopropanol) the down-spikes had started
to become fewer and rare, and it had 490 uHz of Allan Deviation, i.e. 4,9E-11
for tau = 5 s. I beleive it will considerably lower as the spiking stops.
The full 10811 seems powered during standby mode. Some solutions will only have
the oven powered in standby. What does change on powerup of the rest of the
counter is that you turn on alot more heat, current, the fan (which has a fat
metall wall between the flow and the 10811, but that piece of metal wrapps the
10811 so the cool-of-effect may be there never the less.
After putting the lid on and letting it sit there the spikes is still evident
and last reading gives 5,8E-11 @ tau = 5s.
A comperative measure with another 10811 (which I just happend to have a
cable for lying around on the table) but which was unheated also gave time for
a little experiment, looking at the heat-up performance. Now, it started some
200 Hz hot, but went for a steady linear dive downwards which at about 400 s
curved upwards and had a gentle overshot (i.e. lower frequency) until it
stablized. However, subsequent measure showed a slow but steady rise and ADEV
measures was surely limited by the driftrate. It was however much lower, such
as 1.2E-11, and that includes the drift-rate tainting while the display
indicated a much smoother curve.
As I don't have a wiring aisle for my lab-bench (beleive me, I start to
consider it as a must have even if it would be a squeeze-in variant of 3-4
dm or so, I could not get the heated 10811 in my 5372A. I really need to hook
the backside panels up to a BNC patch any decade now. Anyway, otherwise I would
have a well heated alternative to measure on.
I wish I get a phonecall with good news from a fellow time-nut tomorrow. If so
I drive down to him. :-)
Cheers,
Magnus
Magnus Danielson wrote:
Hej Bruce,
Oscillation/cycling of oven temperature?
Oven controller oscillation?
Might be, but then my "loadingcondition" has caused the oven control out of
stability. This would certainly supprice me. The oven control in the 10811 is
linear and for most practical purposes behave like a first-degree linear
diffrential system. OK, there might be a second degree aspect, but the poles
should be fairly stable and it would be more a pure "amplitude" problem.
Now as I was down putting the hood on (and removing some of the residues from
the not so very smart packaging, using isopropanol) the down-spikes had started
to become fewer and rare, and it had 490 uHz of Allan Deviation, i.e. 4,9E-11
for tau = 5 s. I beleive it will considerably lower as the spiking stops.
The full 10811 seems powered during standby mode. Some solutions will only have
the oven powered in standby. What does change on powerup of the rest of the
counter is that you turn on alot more heat, current, the fan (which has a fat
metall wall between the flow and the 10811, but that piece of metal wrapps the
10811 so the cool-of-effect may be there never the less.
After putting the lid on and letting it sit there the spikes is still evident
and last reading gives 5,8E-11 @ tau = 5s.
A comperative measure with another 10811 (which I just happend to have a
cable for lying around on the table) but which was unheated also gave time for
a little experiment, looking at the heat-up performance. Now, it started some
200 Hz hot, but went for a steady linear dive downwards which at about 400 s
curved upwards and had a gentle overshot (i.e. lower frequency) until it
stablized. However, subsequent measure showed a slow but steady rise and ADEV
measures was surely limited by the driftrate. It was however much lower, such
as 1.2E-11, and that includes the drift-rate tainting while the display
indicated a much smoother curve.
As I don't have a wiring aisle for my lab-bench (beleive me, I start to
consider it as a must have even if it would be a squeeze-in variant of 3-4
dm or so, I could not get the heated 10811 in my 5372A. I really need to hook
the backside panels up to a BNC patch any decade now. Anyway, otherwise I would
have a well heated alternative to measure on.
I wish I get a phonecall with good news from a fellow time-nut tomorrow. If so
I drive down to him. :-)
Cheers,
Magnus
Hej Magnus
What I had in mind was perhaps a bad joint or component failure in the
oven regulator due to thermal cycling and or age of the oscillator.
Perhaps the oven regulator compensation capacitor??
Bruce
Hej Magnus
Could there perhaps be an intermittent thermal fuse in the 10811?
Bruce
Hej Magnus
Since the 10811 oven heater supply in a 5370 is unregulated one possible
cause is a quasi periodic variation of the mains supply voltage.
Bruce
I believe it is almost impossible to have an intermittent thermal fuse due
to their very clever design. Although over age they can open up. Once open,
however I do not believe they can connect again. The fuse is simply to
metallic contacts that are force to be in contact during assembly. Their
normal desired resting state would be to be not connected. When closed, the
fuse cavity is filled with wax, which mostly determines when the fuse opens
(temperature). With too much current through the fuse, the wax heats
allowing the contact to spring apart to their normal resting position. Now,
with no more current flowing, the wax hardens almost immediately, never
allowing the two contacts to meet again. - Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Dr Bruce Griffiths
Sent: Sunday, July 22, 2007 9:39 PM
To: Magnus Danielson; Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] HP 5370B low frequency modulation
); SAEximRunCond expanded to false
Errors-To: time-nuts-bounces+mfeher=eozinc.com+mfeher=eozinc.com@febo.com
Hej Magnus
Could there perhaps be an intermittent thermal fuse in the 10811?
Bruce
Mike Feher wrote:
); SAEximRunCond expanded to false
Errors-To: time-nuts-bounces+bruce.griffiths=xtra.co.nz+bruce.griffiths=xtra.co.nz@febo.com
I believe it is almost impossible to have an intermittent thermal fuse due
to their very clever design. Although over age they can open up. Once open,
however I do not believe they can connect again. The fuse is simply to
metallic contacts that are force to be in contact during assembly. Their
normal desired resting state would be to be not connected. When closed, the
fuse cavity is filled with wax, which mostly determines when the fuse opens
(temperature). With too much current through the fuse, the wax heats
allowing the contact to spring apart to their normal resting position. Now,
with no more current flowing, the wax hardens almost immediately, never
allowing the two contacts to meet again. - Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
Mike
Whilst the fuse itself may not be the problem, it is a plugin component
and the contacts may be problematic.
Bruce
Highly unlikely, but, possible, especially if it was in a corrosive
atmosphere. Of course then I would expect to see evidence of corrosion on
other components. When we do not know the answer we can come up with so many
possibilities and not have one of them correct. I have run across a lot of
those defective fuses over the years as HP has been using them forever.
There was no real evidence as to why they opened, and that is why before I
guessed at just plain ageing and the wax eventually getting soft. I just
checked the current flow within the oscillator where the fuse used to be
plugged in, which was at least nice of them, and always found it to be
normal. I just took a piece of buss wire and plugged it into the same two
pins were the fuse used to be and never had a problem again. The situation
Magnus describes of course is very unusual, and, in reality would only be
found by a time nut as it is so miniscule. There is also some periodicity to
it, which does suggest some control loop problem, but, I would hate to even
take a guess. - Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Dr Bruce Griffiths
Sent: Sunday, July 22, 2007 10:32 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] HP 5370B low frequency modulation
Mike Feher wrote:
); SAEximRunCond expanded to false
Errors-To:
time-nuts-bounces+bruce.griffiths=xtra.co.nz+bruce.griffiths=xtra.co.nz@febo
.com
I believe it is almost impossible to have an intermittent thermal fuse due
to their very clever design. Although over age they can open up. Once
open,
however I do not believe they can connect again. The fuse is simply to
metallic contacts that are force to be in contact during assembly. Their
normal desired resting state would be to be not connected. When closed,
the
fuse cavity is filled with wax, which mostly determines when the fuse
opens
(temperature). With too much current through the fuse, the wax heats
allowing the contact to spring apart to their normal resting position.
Now,
with no more current flowing, the wax hardens almost immediately, never
allowing the two contacts to meet again. - Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
Mike
Whilst the fuse itself may not be the problem, it is a plugin component
and the contacts may be problematic.
Bruce
From: "Mike Feher" mfeher@eozinc.com
Subject: Re: [time-nuts] HP 5370B low frequency modulation
Date: Sun, 22 Jul 2007 22:58:00 -0400
Message-ID: 00b101c7ccd5$490ae6a0$0201a8c0@gsmacdq14es
Mike,
Highly unlikely, but, possible, especially if it was in a corrosive
atmosphere. Of course then I would expect to see evidence of corrosion on
other components. When we do not know the answer we can come up with so many
possibilities and not have one of them correct. I have run across a lot of
those defective fuses over the years as HP has been using them forever.
There was no real evidence as to why they opened, and that is why before I
guessed at just plain ageing and the wax eventually getting soft. I just
checked the current flow within the oscillator where the fuse used to be
plugged in, which was at least nice of them, and always found it to be
normal. I just took a piece of buss wire and plugged it into the same two
pins were the fuse used to be and never had a problem again. The situation
Magnus describes of course is very unusual, and, in reality would only be
found by a time nut as it is so miniscule. There is also some periodicity to
it, which does suggest some control loop problem, but, I would hate to even
take a guess. - Mike
May I also point out that there may be as low as short low period per 1000 s or
about 3-8 (rought estimate).
I am considering all kinds of possible reasons for it. The group certainly has
more experience shared among them than I have on these, so I concentrate on
observations.
I wonder if it may be some form of initial shock burnout that I am witnessing.
I have no idea how they are suppposed to look. It is not like you want to toss
your 10811s to the floor just to see how they behave as a result, now is there?
If I where making them I would, but with a thad more of science attached to it.
Cheers,
Magnus