Re: [time-nuts] Z3801A OCXO manual trimming

[paul swed]

Someone mentioned the right non-lazy approach with a summing/offset opamp.
Do agree. But then just for a try use a V supply and a 10K.
I seem to recall tracing the DAC to an opamp. The EFC line is pretty easily
accessed.
Its one of the little coax cables.
The other even lower risk approach is disconnect the coax and see what
voltage is required to 0 out the 10 MHz.
How far away is it from the DAC feeding the coax connector.
Regards
Paul

On Tue, Mar 6, 2018 at 9:40 AM, Bob kb8tq  wrote:

> Hi
>
> Assuming you can break the EFC lead to the OCXO, you aren’t going to
> damage anything
> inside by feeding the EFC line with +/- 5V. If you are going to tear open
> the OCXO, the line
> will need to be pulled anyway. Without knowing what they drive the EFC
> line with, it’s hard to
> know if the driver on the line would be happy with a back fed voltage.
> Best to be careful ….
>
> Bob
>
> > On Mar 6, 2018, at 3:30 AM, gandalfg8--- via time-nuts <
> time-nuts@febo.com> wrote:
> >
> >
> >
> >
> >
> > Crazy thought.Could you just force a DC offset into the EFC assuming the
> > internal varicap is not out of range.
> > It would be simply adding a resistor to pull up or down to see if you can
> > get a bit of pull and allow the dac to move back in range a bit. Its a
> band
> > aid.
> > I know its sort of crazy. But ripping the oven apart really is no fun at
> > all.
> > Regards
> > Paul
> > WB8TSL
> >
> >
> >
> > **
> >
> > Not really such a crazy thought, I've done this on a Trimble-Nortel
> NTGS50AA where the original 34310-T oscillator had "aged" beyond the 3 to 6
> Volt EFC range.
> >
> > On a unit that was refusing to lock the oscillator was removed and
> confirmed to require an EFC voltage of approx 6.5 Volts for an output
> frequency of 10 MHz. As other tested samples of this oscillator, although
> admittedly not many, required around 4.5 volts there does remain the
> possibility of an actual internal fault but it did test on the bench as
> otherwise ok.
> >
> > Using a simple unity gain level shifter based on a few resistors and a
> TL071 op amp, just because there was one to hand, the EFC voltage from the
> control circuit was shifted 2 Volts high and the unit then behaved as
> expected.
> >
> > The effects of temperature, supply variation, etc on the modified
> circuit were not investigated as this was only a short term test but it
> certainly looked to be a viable proposition, to the extent that rather than
> fit a replaccement 34310-T that board was fitted with SMB connectors using
> the pads provided to keep as a test bed.
> >
> > Nigel GM8PZR
> >
> >
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[time-nuts] Z3801A OCXO manual trimming

[Joe Hobart]

Success!

I disassembled the oven and adjusted the OCXO frequency up about 5 Hz.  Lady
Heather reported the DAC changed from +99.99% with no lock to -90% with lock to
GPS.  Hopefully I did not increase the frequency too much.  The long term
aging/drift direction has been down - which caused the loss of lock.  At this
time the DAC has increased slightly to -90.5 as the system settles.

Paul, I also thought about adding an offset voltage to the DAC, but I was
concerned about stability.

Adrian, I thought about an access hole, but when I disassembled the oven, a
piece of the outer heater was partially covering the adjustment access cover and
adjustment.  That required careful moving to access the oscillator adjustment.

Disassembling (ripping is more descriptive) the oven was not difficult.  Putting
everything back together was more tedious.

A huge thanks for all the replies, links to pictures, encouragement, etc.

Joe, W7LUX
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Re: [time-nuts] Z3801A OCXO manual trimming

[Bob kb8tq]

Hi

Assuming you can break the EFC lead to the OCXO, you aren’t going to damage 
anything 
inside by feeding the EFC line with +/- 5V. If you are going to tear open the 
OCXO, the line
will need to be pulled anyway. Without knowing what they drive the EFC line 
with, it’s hard to
know if the driver on the line would be happy with a back fed voltage. Best to 
be careful ….

Bob

> On Mar 6, 2018, at 3:30 AM, gandalfg8--- via time-nuts  
> wrote:
> 
> 
> 
> 
> 
> Crazy thought.Could you just force a DC offset into the EFC assuming the
> internal varicap is not out of range.
> It would be simply adding a resistor to pull up or down to see if you can
> get a bit of pull and allow the dac to move back in range a bit. Its a band
> aid.
> I know its sort of crazy. But ripping the oven apart really is no fun at
> all.
> Regards
> Paul
> WB8TSL
> 
> 
> 
> **
> 
> Not really such a crazy thought, I've done this on a Trimble-Nortel NTGS50AA 
> where the original 34310-T oscillator had "aged" beyond the 3 to 6 Volt EFC 
> range.
> 
> On a unit that was refusing to lock the oscillator was removed and confirmed 
> to require an EFC voltage of approx 6.5 Volts for an output frequency of 10 
> MHz. As other tested samples of this oscillator, although admittedly not 
> many, required around 4.5 volts there does remain the possibility of an 
> actual internal fault but it did test on the bench as otherwise ok.
> 
> Using a simple unity gain level shifter based on a few resistors and a TL071 
> op amp, just because there was one to hand, the EFC voltage from the control 
> circuit was shifted 2 Volts high and the unit then behaved as expected.
> 
> The effects of temperature, supply variation, etc on the modified circuit 
> were not investigated as this was only a short term test but it certainly 
> looked to be a viable proposition, to the extent that rather than fit a 
> replaccement 34310-T that board was fitted with SMB connectors using the pads 
> provided to keep as a test bed.
> 
> Nigel GM8PZR
> 
> 
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Re: [time-nuts] Z3801A OCXO manual trimming

[Bob kb8tq]

Hi

The control range should be +/- 5V if I remember correctly. If it’s not, the
only other standard would be 0-5V. There is zero logic in running a wider
swing mod to an OCXO at a lower EFC range. 

It indeed sounds like the DAC has trouble. 

Bob

> On Mar 6, 2018, at 1:24 AM, Mark Sims  wrote:
> 
> I'm not sure what the Z3801A uses for EFC range.   Heather uses the EFC 
> relative command to report the EFC setting.  That command reports values from 
> -100% to 100%.   There is a command that reports the DAC input in counts, but 
> nothing documented that shows volts/count.
> 
> Since the DAC is at -2V with a 99+% DAC setting, it looks like the DAC 
> circuit has issues, or power supply problems.   I think the DAC circuit is a 
> 16 bit DAC with 4 more bits of resolution created by dithering the DAC inputs.
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Re: [time-nuts] Z3801A OCXO manual trimming

[gandalfg8--- via time-nuts]

 


Crazy thought.Could you just force a DC offset into the EFC assuming the
internal varicap is not out of range.
It would be simply adding a resistor to pull up or down to see if you can
get a bit of pull and allow the dac to move back in range a bit. Its a band
aid.
I know its sort of crazy. But ripping the oven apart really is no fun at
all.
Regards
Paul
WB8TSL

 

**

Not really such a crazy thought, I've done this on a Trimble-Nortel NTGS50AA 
where the original 34310-T oscillator had "aged" beyond the 3 to 6 Volt EFC 
range.

On a unit that was refusing to lock the oscillator was removed and confirmed to 
require an EFC voltage of approx 6.5 Volts for an output frequency of 10 MHz. 
As other tested samples of this oscillator, although admittedly not many, 
required around 4.5 volts there does remain the possibility of an actual 
internal fault but it did test on the bench as otherwise ok.

Using a simple unity gain level shifter based on a few resistors and a TL071 op 
amp, just because there was one to hand, the EFC voltage from the control 
circuit was shifted 2 Volts high and the unit then behaved as expected.

The effects of temperature, supply variation, etc on the modified circuit were 
not investigated as this was only a short term test but it certainly looked to 
be a viable proposition, to the extent that rather than fit a replaccement 
34310-T that board was fitted with SMB connectors using the pads provided to 
keep as a test bed.

Nigel GM8PZR


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[time-nuts] Z3801A OCXO manual trimming

[Mark Sims]

I'm not sure what the Z3801A uses for EFC range.   Heather uses the EFC 
relative command to report the EFC setting.  That command reports values from 
-100% to 100%.   There is a command that reports the DAC input in counts, but 
nothing documented that shows volts/count.

Since the DAC is at -2V with a 99+% DAC setting, it looks like the DAC circuit 
has issues, or power supply problems.   I think the DAC circuit is a 16 bit DAC 
with 4 more bits of resolution created by dithering the DAC inputs.
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Re: [time-nuts] Z3801A OCXO manual trimming

[Tom Curlee]

What is the rail to rail EFC voltage on the Z3801A?  Is it different than the 
single oven 10811?  My 10811 manual says that the EFC is -5V to +5V, while the 
EFC voltage on my ailing Z3801 is ~-2.0V with LH reporting the DAC at 
99.996902%.
Haven't had time to dig any further - been moving/installing antennas including 
one of my GPS antennas.


  From: Mark Sims <hol...@hotmail.com>
 To: "time-nuts@febo.com" <time-nuts@febo.com> 
 Sent: Monday, March 5, 2018 7:36 PM
 Subject: [time-nuts] Z3801A OCXO manual trimming
   
Or, it you are sure it's the OCXO,  go shopping for a new one.    There is a 
reputable seller with them (the double oven version) for $100 on Ebay.

A couple of things to try...  monitor the EFC voltage, power up the unit, and 
see if it is changing as it attempts to lock.  If  it does not, you may have a 
DAC problem... I don't think the Z3801 remembers the last DAC voltage to speed 
up the initial lock, so it should be searching for the lock voltage.

Also monitor the OCXO output and see how it changes as it warms up.  It should 
start out several Hz off and converge to 10 MHz as it warms up.  



> Either tear into the OCXO or go shopping for a new(er) GPSDO.
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[time-nuts] Z3801A OCXO manual trimming

[Mark Sims]

Or, it you are sure it's the OCXO,   go shopping for a new one.There is a 
reputable seller with them (the double oven version) for $100 on Ebay.

A couple of things to try...  monitor the EFC voltage, power up the unit, and 
see if it is changing as it attempts to lock.   If  it does not, you may have a 
DAC problem... I don't think the Z3801 remembers the last DAC voltage to speed 
up the initial lock, so it should be searching for the lock voltage.

Also monitor the OCXO output and see how it changes as it warms up.   It should 
start out several Hz off and converge to 10 MHz as it warms up.   



> Either tear into the OCXO or go shopping for a new(er) GPSDO.
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Re: [time-nuts] Z3801A OCXO manual trimming

[rfnuts]

The easiest solution would be to drill a hole in the right place in
order to access the screw that covers the trimmer hole of the inner OCXO
housing.

Does anyone have a disassembled double oven 10811 at hands and could
take the required measures plus check if any vital parts of the outer
oven are in the way?

Adrian

Am 03.03.2018 um 19:37 schrieb Tom Curlee:
> Since the Z3801A is being discussed, I thought I'd ask about an issue I'm 
> having with my unit.  I use my Z3801 as my working lab standard for the usual 
> pieces of RF test equipment.  In the past year or so I've had the unit drop 
> out of lock and go into standby mode.  Resetting/cycling power would bring it 
> back into lock for a while, but it generally got worse and now stays in hold 
> over mode.  LH (thanks Mark Sims!!) reports that everything is operating 
> normally except that the it has a PLL unlock.  The one highly suspicious item 
> is that the DAC is at 99.996902% - full output.
> The unit shows it has over 94.5K hours run time, so I suspect that the OCXO 
> has aged to the point that the EFC can't pull it into lock.  I disassembled 
> the OCXO to see if it had a trimmer capacitor like the standard 10811 units.  
> After removing the outer case and foam insulation, I see that the outer 
> heater is one of the thin printed circuit serpentine heaters on what I think 
> is Kapton.  That would need to be peeled off of the case to either get to the 
> hole for the trimmer (if there is one) or to remove the cover for the inner 
> case.
> What I don't understand is the purpose of what looks like another coil or 
> heater wrapped around the Kapton printed circuit heater stuck to the inner 
> case.  This second coil/heater is 2 layers of 1/8" thick red foam wrapped 
> completely around the inner case, with fine copper wires wrapped over each 
> layer.  At least I think there are wires on each layer.  This whole second 
> heater is taped down and I don't want to dig any further until I know a bit 
> more about what I'm doing or find that there isn't a trimmer on the double 
> oven 10811 oscillators.
> Any ideas on the purpose of the outer heater (or whatever it is)?  Does the 
> double oven 10811 have a manual trimmer that I can adjust to bring the 
> oscillator back to the center of the EFC range?  Assuming that I can manually 
> adjust the OCXO back into adjustment range, will there be any issues with the 
> Z3801 performance, things like phase noise, short term stability, etc?
> Any suggestions will be most appreciated.
> Thanks,
> Tom
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Re: [time-nuts] Z3801A OCXO manual trimming

[Bob kb8tq]

Hi

Either tear into the OCXO or go shopping for a new(er) GPSDO. The
Z38xx devices all had a lot more in common with each other than they
did differences. The OCXO design changed from the 10811 to various
more modern designs. The disciplining process seems to have remained
pretty much the same over the years. 

Bob

> On Mar 5, 2018, at 11:21 AM, Joe Hobart  wrote:
> 
> 
> Thank you, Hal, for these links and to others for your comments.
> 
> Setting the oven temperature on a turning point appears tedious.  Perhaps 
> there
> is enough range in the frequency adjustment to put the oscillator back on
> frequency - or close enough for the EFC to be effective.  If not, I may have 
> to
> adjust the temperature, but time is limited.
> 
> Some measurements with the EFC disconnected and a calibrated frequency 
> counter:
> 
> .815  KHz  at Z3801A turn on
> 
> .9984 KHz  highest frequency seen (temperature overshoot)
> 
> .9947 KHz  approximate final frequency
> 
> The EFC does have wide range; it can almost pull the 5.3 Hz offset onto 
> frequency.
> 
> Thanks again,
> Joe, W7LUX
> 
> 
>> Does the oscillator have an adjustment?  If so, is this somewhat accessible
>> without destroying the assembly?  Are there pictures of the oscillator
>> assembly?
> 
> https://www.realhamradio.com/GPS-oven-journey.htm
> 
> https://www.realhamradio.com/z3801a-turning-point.htm
> 
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Re: [time-nuts] Z3801A OCXO manual trimming

[paul swed]

Crazy thought.Could you just force a DC offset into the EFC assuming the
internal varicap is not out of range.
It would be simply adding a resistor to pull up or down to see if you can
get a bit of pull and allow the dac to move back in range a bit. Its a band
aid.
I know its sort of crazy. But ripping the oven apart really is no fun at
all.
Regards
Paul
WB8TSL

On Mon, Mar 5, 2018 at 11:21 AM, Joe Hobart  wrote:

>
> Thank you, Hal, for these links and to others for your comments.
>
> Setting the oven temperature on a turning point appears tedious.  Perhaps
> there
> is enough range in the frequency adjustment to put the oscillator back on
> frequency - or close enough for the EFC to be effective.  If not, I may
> have to
> adjust the temperature, but time is limited.
>
> Some measurements with the EFC disconnected and a calibrated frequency
> counter:
>
>  .815  KHz  at Z3801A turn on
>
>  .9984 KHz  highest frequency seen (temperature overshoot)
>
>  .9947 KHz  approximate final frequency
>
> The EFC does have wide range; it can almost pull the 5.3 Hz offset onto
> frequency.
>
> Thanks again,
> Joe, W7LUX
>
>
> > Does the oscillator have an adjustment?  If so, is this somewhat
> accessible
> > without destroying the assembly?  Are there pictures of the oscillator
> > assembly?
>
> https://www.realhamradio.com/GPS-oven-journey.htm
>
> https://www.realhamradio.com/z3801a-turning-point.htm
>
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Re: [time-nuts] Z3801A OCXO manual trimming

[Joe Hobart]

Thank you, Hal, for these links and to others for your comments.

Setting the oven temperature on a turning point appears tedious.  Perhaps there
is enough range in the frequency adjustment to put the oscillator back on
frequency - or close enough for the EFC to be effective.  If not, I may have to
adjust the temperature, but time is limited.

Some measurements with the EFC disconnected and a calibrated frequency counter:

 .815  KHz  at Z3801A turn on

 .9984 KHz  highest frequency seen (temperature overshoot)

 .9947 KHz  approximate final frequency

The EFC does have wide range; it can almost pull the 5.3 Hz offset onto 
frequency.

Thanks again,
Joe, W7LUX


> Does the oscillator have an adjustment?  If so, is this somewhat accessible
> without destroying the assembly?  Are there pictures of the oscillator
> assembly?

https://www.realhamradio.com/GPS-oven-journey.htm

https://www.realhamradio.com/z3801a-turning-point.htm

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Re: [time-nuts] Z3801A OCXO manual trimming

[paul swed]

I dug in deep and there is an adjustment. Thats the great news. The bad
news was never able to put the oven back together.
It was a mess. The insulation stuff deteriorated. (Might mean over heated
oven)
The various wires going to the oscillator are wrapped about 4 times around
the oven. I am sure the reason is to stop temperature variations but seems
painful.
Regards
Paul
WB8TSL

On Sun, Mar 4, 2018 at 11:38 PM, Hal Murray  wrote:

>
> n...@npgcable.com said:
> > Does the oscillator have an adjustment?  If so, is this somewhat
> accessible
> > without destroying the assembly?  Are there pictures of the oscillator
> > assembly?
>
> https://www.realhamradio.com/GPS-oven-journey.htm
>
> https://www.realhamradio.com/z3801a-turning-point.htm
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
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[time-nuts] Z3801A OCXO manual trimming

[Mark Sims]

Oops... I checked and the Z38xx devices don't have a DAC setting command.  It 
was the UCCM GPSDOs that have a SCPI command for controlling the DAC manually,

-

> When I press "D" Lady Heather replies:
Manual disciplining not supported by this receiverpress ESC
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Re: [time-nuts] Z3801A OCXO manual trimming

[Hal Murray]

n...@npgcable.com said:
> Does the oscillator have an adjustment?  If so, is this somewhat accessible
> without destroying the assembly?  Are there pictures of the oscillator
> assembly? 

https://www.realhamradio.com/GPS-oven-journey.htm

https://www.realhamradio.com/z3801a-turning-point.htm


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Z3801A OCXO manual trimming

[Bob kb8tq]

Hi

> On Mar 4, 2018, at 10:30 PM, Joe Hobart  wrote:
> 
> 
> Mark,
> 
> When I press "D" Lady Heather replies:
> 
> Manual disciplining not supported by this receiverpress ESC
> 
> 
> Questions about the Z3801A:
> 
> Does the oscillator have an adjustment?  If so, is this somewhat accessible

Yes, if you dig deep enough

> without destroying the assembly?

Depends on how good you are at ripping into things 

>  Are there pictures of the oscillator assembly?

I believe there are in the archives

> 
> Is there an adjustment for temperature?

Yes, by changing the select resistor 

>  Is this accessible?

Yes, once you have the inside oven board out of the enclosure. Accessible is a 
relative term. I would not dig that deep. Others on the list seem to be happy 
going
that far into the assembly. 

Bob

> 
> Thanks,
> Joe, W7LUX
> 
> 
> Lady Heather has a command that lets you set the DAC voltage.  It's in the "D"
> menu.   Depending upon the firmware, you may need to disable disciplining 
> first
> (also in the "D" menu).  If the DAC  command works to change the OCXO freq,  
> the
> osc EFC and DAC are probably OK.  If it does not, I'd suspect the DAC or the
> osc EFC input... or perhaps your firmware does no support the DAC setting 
> command.
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Re: [time-nuts] Z3801A OCXO manual trimming

[Joe Hobart]

Mark,

When I press "D" Lady Heather replies:

Manual disciplining not supported by this receiverpress ESC


Questions about the Z3801A:

Does the oscillator have an adjustment?  If so, is this somewhat accessible
without destroying the assembly?  Are there pictures of the oscillator assembly?

Is there an adjustment for temperature?  Is this accessible?

Thanks,
Joe, W7LUX


Lady Heather has a command that lets you set the DAC voltage.  It's in the "D"
menu.   Depending upon the firmware, you may need to disable disciplining first
(also in the "D" menu).  If the DAC  command works to change the OCXO freq,  the
osc EFC and DAC are probably OK.  If it does not, I'd suspect the DAC or the
osc EFC input... or perhaps your firmware does no support the DAC setting 
command.
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[time-nuts] Z3801A OCXO manual trimming

[Mark Sims]

Lady Heather has a command that lets you set the DAC voltage.  It's in the "D" 
menu.   Depending upon the firmware, you may need to disable disciplining first 
(also in the "D" menu).  If the DAC  command works to change the OCXO freq,  
the osc EFC and DAC are probably OK.  If it does not, I'd suspect the DAC or 
the  osc EFC input... or perhaps your firmware does no support the DAC setting 
command.
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Re: [time-nuts] Z3801A OCXO manual trimming

[Bob kb8tq]

Hi

> On Mar 4, 2018, at 1:13 PM, Joe Hobart  wrote:
> 
> My Z3801A failed about a year ago (there was a warning the electronic 
> frequency
> control was nearing a limit).
> 
> Symptoms (most from GPS Control and Lady Heather:
> 
>   Frequency about 1E-8 low
> 
>   Time Invalid  (many hours off)
>   Date 6 months old
>   DAC 99.9969 percent
>   Life 72K Hours
> 
> Lady Heather shows the following as OK:
> 
>   ROM, RAM, OSC GPS, Power, EEPROM, Antenna, Discipline, 5 satellites
> 
> GPS Con shows the following:
> 
>   EFC: ERR
>   No time display
>   Outputs Invalid
> 
> Only the front panel power light is lit.
> 
> This suggests either the crystal has aged or the heater temperature has 
> drifted
> slightly.  I hear/read that opening the oscillator is difficult.  Is there a
> usable adjustment?
> 
> What have others done to restore operation?  Is it time to consider a 
> different
> time & frequency standard?

With enough effort and enough time spent troubleshooting, you probably can 
fix the beast. You might have to swap out the OCXO, but that’s still just a 
repair
process. The bigger question is indeed how much work to put in. 

The basic approach is to fire up a counter and get into the EFC voltage line.
Swing it to both limits and see what the frequency does. That will give you 
an idea if it’s the OCXO or if it’s the DAC side of things. 

The 3801 was made for a while. Some are hitting 20 years old at this point. 
Mine seem to eat power supply components from time to time. One of these
days, whatever it is that pops the fuse will do more damage. 

Back when the 3801 hit the surplus market there really was not a whole lot
else to look at. These days, we’re hip deep in a whole range of units sourced
mostly from “China Electronic Salvage Inc”.  Who knows …. maybe one day
there will be another TimeNuts TBolt “sale”…..

Bob


> 
> Thanks,
> Joe, W7LUX
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Re: [time-nuts] Z3801A OCXO manual trimming

[Joe Hobart]

My Z3801A failed about a year ago (there was a warning the electronic frequency
control was nearing a limit).

Symptoms (most from GPS Control and Lady Heather:

   Frequency about 1E-8 low

   Time Invalid  (many hours off)
   Date 6 months old
   DAC 99.9969 percent
   Life 72K Hours

Lady Heather shows the following as OK:

   ROM, RAM, OSC GPS, Power, EEPROM, Antenna, Discipline, 5 satellites

GPS Con shows the following:

   EFC: ERR
   No time display
   Outputs Invalid

Only the front panel power light is lit.

This suggests either the crystal has aged or the heater temperature has drifted
slightly.  I hear/read that opening the oscillator is difficult.  Is there a
usable adjustment?

What have others done to restore operation?  Is it time to consider a different
time & frequency standard?

Thanks,
Joe, W7LUX
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Re: [time-nuts] Z3801A OCXO manual trimming

[Bob kb8tq]

Hi

Heater failure is pretty easy to spot. You will be *way* off frequency. No need 
for a 
GPSDO in your counter to see if it’s out by 0.0001 Hz. You should be > 20 Hz low
in frequency. Since there *are* multiple heaters, there are some odd 
combinations
in a 3801. Your inner heater can be dead, but the outer heater still works. The 
unit
will look like it’s warming up but doing so *really* slowly. 

Based on seeing a lot of 10811’s and a lot of modern OCXO’s, a crystal that 
ages out
is pretty rare. The “something else” category is way more likely when diving 
into one
that is off frequency. That wasn’t always true so you can go back far enough in 
time 
(like into the 60’s) and find units that have aged out. They also aged out in 
the first 
ten years after they left the factory. Things got a lot better over the years 
in terms of
long term precision crystal aging ….

Bob

> On Mar 3, 2018, at 10:12 PM, Tom Holmes <thol...@woh.rr.com> wrote:
> 
> Bob...
> 
> Interesting point about the heater not working vs the XTAL having drifted too 
> far. Mine has the same symptoms as the others reported (EFC at the end of its 
> rope) but have not tackled it yet, figuring I'd have to dismantle the whole 
> thing. Certainly troubleshooting a non-operating heater would be much more 
> pleasant.
> 
> Thanks for that insight.
> 
> Tom Holmes, N8ZM
> 
> -Original Message-
> From: time-nuts <time-nuts-boun...@febo.com> On Behalf Of Bob kb8tq
> Sent: Saturday, March 03, 2018 2:07 PM
> To: Tom Curlee <tcur...@sbcglobal.net>; Discussion of precise time and 
> frequency measurement <time-nuts@febo.com>
> Subject: Re: [time-nuts] Z3801A OCXO manual trimming
> 
> Hi
> 
> First off some basics about OCXO’s.
> 
> In a single oven design, you have a heater that warms up the entire crystal 
> and the guts of the oscillator. It is on all the time and 
> it gets things up to a temperature that makes sense for a given crystal. It 
> can be adjusted based on manufacturing data or by 
> trial and error to match the characteristics of that crystal. 
> 
> In a double oven design, you have two ovens that are on all the time. One 
> heats up the other one. They both work together to
> achieve the end result. The gain of one adds to the gain of the other to give 
> an improved result. On some double ovens, the 
> entire heat range of the inner oven is only 10’s of degrees ….
> 
> In a boosted oven, you have a second heater to get things going when it is 
> very cold. This is an unusual approach and rarely 
> seen. Its normally easier to just design a bit more power into the main oven 
> circuit. In a boosted design, the boost heat goes
> away in normal operation at typical temperatures. In normal operation, the 
> gain of the boost circuit does not count. 
> 
> SO ….
> 
> The oscillator in the Z3801 is a boosted 10811. It is boosted to allow them 
> to hit a spec of -40C on the unit. At the time it was
> designed, there was talk about mounting these things in un-heated boxes 
> outdoors. After they got a bit further into all the 
> details of the designs … that part went away. The spec still hung around long 
> enough to apply to very early designs. 
> 
> The net result is that you can pretty much destroy the outer heater stuff and 
> the oscillator will work fine. There is no need 
> for it in a typical lab. There are some alarm triggers that need to be wired 
> “ok” when you do so. The details are in the archives. 
> 
> But …
> 
> Best guess if your unit is at max EFC = the “real” heater on the 10811 has 
> quit working. To get at that, you will need to dig 
> into the guts of the unit. Given the massive EFC on the Z3801 version of the 
> oscillator, it would take a crazy amount of aging
> to hit limit.
> 
> Bob
> 
> 
>> On Mar 3, 2018, at 1:37 PM, Tom Curlee <tcur...@sbcglobal.net> wrote:
>> 
>> Since the Z3801A is being discussed, I thought I'd ask about an issue I'm 
>> having with my unit.  I use my Z3801 as my working lab standard for the 
>> usual pieces of RF test equipment.  In the past year or so I've had the unit 
>> drop out of lock and go into standby mode.  Resetting/cycling power would 
>> bring it back into lock for a while, but it generally got worse and now 
>> stays in hold over mode.  LH (thanks Mark Sims!!) reports that everything is 
>> operating normally except that the it has a PLL unlock.  The one highly 
>> suspicious item is that the DAC is at 99.996902% - full output.
>> The unit shows it has over 94.5K hours run time, so I suspect that the OCXO 
>> has aged to the point that the EFC can't pull it into lock.  I disassembled 
>> the OCXO to see if it had a trimmer capacitor like the standard 

Re: [time-nuts] Z3801A OCXO manual trimming

[Tom Van Baak]

> Interesting point about the heater not working vs. the XTAL having drifted 
> too far.

Any logs you made of EFC percent over the past few months or years will help 
verify the off-the-rail theory.

Another thing to try -- turn-off the Z3801A for a couple of hours to let it 
cool. Disconnect the GPS antenna. Then power it up and monitor the frequency, 
say every 10 s or a minute, until it stabilizes. The shape of this warm-up 
curve will give you a hint if the oven(s) are working. Repeat the test with the 
outer oven disconnected to test the inner oven by itself.

/tvb

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Re: [time-nuts] Z3801A OCXO manual trimming

[Bruce Griffiths]

Monitoring the output frequency whilst the oven "heats" up may give additional 
clues as will monitoring the heater current.

Bruce

> 
> On 04 March 2018 at 16:12 Tom Holmes <thol...@woh.rr.com> wrote:
> 
> Bob...
> 
> Interesting point about the heater not working vs the XTAL having drifted 
> too far. Mine has the same symptoms as the others reported (EFC at the end of 
> its rope) but have not tackled it yet, figuring I'd have to dismantle the 
> whole thing. Certainly troubleshooting a non-operating heater would be much 
> more pleasant.
> 
> Thanks for that insight.
> 
> Tom Holmes, N8ZM
> 
> -Original Message-
> From: time-nuts <time-nuts-boun...@febo.com> On Behalf Of Bob kb8tq
> Sent: Saturday, March 03, 2018 2:07 PM
> To: Tom Curlee <tcur...@sbcglobal.net>; Discussion of precise time and 
> frequency measurement <time-nuts@febo.com>
> Subject: Re: [time-nuts] Z3801A OCXO manual trimming
> 
> Hi
> 
> First off some basics about OCXO’s.
> 
> In a single oven design, you have a heater that warms up the entire 
> crystal and the guts of the oscillator. It is on all the time and
> it gets things up to a temperature that makes sense for a given crystal. 
> It can be adjusted based on manufacturing data or by
> trial and error to match the characteristics of that crystal.
> 
> In a double oven design, you have two ovens that are on all the time. One 
> heats up the other one. They both work together to
> achieve the end result. The gain of one adds to the gain of the other to 
> give an improved result. On some double ovens, the
> entire heat range of the inner oven is only 10’s of degrees ….
> 
> In a boosted oven, you have a second heater to get things going when it 
> is very cold. This is an unusual approach and rarely
> seen. Its normally easier to just design a bit more power into the main 
> oven circuit. In a boosted design, the boost heat goes
> away in normal operation at typical temperatures. In normal operation, 
> the gain of the boost circuit does not count.
> 
> SO ….
> 
> The oscillator in the Z3801 is a boosted 10811. It is boosted to allow 
> them to hit a spec of -40C on the unit. At the time it was
> designed, there was talk about mounting these things in un-heated boxes 
> outdoors. After they got a bit further into all the
> details of the designs … that part went away. The spec still hung around 
> long enough to apply to very early designs.
> 
> The net result is that you can pretty much destroy the outer heater stuff 
> and the oscillator will work fine. There is no need
> for it in a typical lab. There are some alarm triggers that need to be 
> wired “ok” when you do so. The details are in the archives.
> 
> But …
> 
> Best guess if your unit is at max EFC = the “real” heater on the 10811 
> has quit working. To get at that, you will need to dig
> into the guts of the unit. Given the massive EFC on the Z3801 version of 
> the oscillator, it would take a crazy amount of aging
> to hit limit.
> 
> Bob
> 
> > > 
> > On Mar 3, 2018, at 1:37 PM, Tom Curlee <tcur...@sbcglobal.net> 
> > wrote:
> > 
> > Since the Z3801A is being discussed, I thought I'd ask about an 
> > issue I'm having with my unit. I use my Z3801 as my working lab standard 
> > for the usual pieces of RF test equipment. In the past year or so I've had 
> > the unit drop out of lock and go into standby mode. Resetting/cycling power 
> > would bring it back into lock for a while, but it generally got worse and 
> > now stays in hold over mode. LH (thanks Mark Sims!!) reports that 
> > everything is operating normally except that the it has a PLL unlock. The 
> > one highly suspicious item is that the DAC is at 99.996902% - full output.
> > The unit shows it has over 94.5K hours run time, so I suspect that 
> > the OCXO has aged to the point that the EFC can't pull it into lock. I 
> > disassembled the OCXO to see if it had a trimmer capacitor like the 
> > standard 10811 units. After removing the outer case and foam insulation, I 
> > see that the outer heater is one of the thin printed circuit serpentine 
> > heaters on what I think is Kapton. That would need to be peeled off of the 
> > case to either get to the hole for the trimmer (if there is one) or to 
> > remove the cover for the inner case.
> > What I don't understand is the purpose of what looks like another 
> > coil or heater wrapped around the Kapton printed circuit heater stuck to 
> >

Re: [time-nuts] Z3801A OCXO manual trimming

[Tom Holmes]

Bob...

Interesting point about the heater not working vs the XTAL having drifted too 
far. Mine has the same symptoms as the others reported (EFC at the end of its 
rope) but have not tackled it yet, figuring I'd have to dismantle the whole 
thing. Certainly troubleshooting a non-operating heater would be much more 
pleasant.

Thanks for that insight.

Tom Holmes, N8ZM

-Original Message-
From: time-nuts <time-nuts-boun...@febo.com> On Behalf Of Bob kb8tq
Sent: Saturday, March 03, 2018 2:07 PM
To: Tom Curlee <tcur...@sbcglobal.net>; Discussion of precise time and 
frequency measurement <time-nuts@febo.com>
Subject: Re: [time-nuts] Z3801A OCXO manual trimming

Hi

First off some basics about OCXO’s.

In a single oven design, you have a heater that warms up the entire crystal and 
the guts of the oscillator. It is on all the time and 
it gets things up to a temperature that makes sense for a given crystal. It can 
be adjusted based on manufacturing data or by 
trial and error to match the characteristics of that crystal. 

In a double oven design, you have two ovens that are on all the time. One heats 
up the other one. They both work together to
achieve the end result. The gain of one adds to the gain of the other to give 
an improved result. On some double ovens, the 
entire heat range of the inner oven is only 10’s of degrees ….

In a boosted oven, you have a second heater to get things going when it is very 
cold. This is an unusual approach and rarely 
seen. Its normally easier to just design a bit more power into the main oven 
circuit. In a boosted design, the boost heat goes
away in normal operation at typical temperatures. In normal operation, the gain 
of the boost circuit does not count. 

SO ….

The oscillator in the Z3801 is a boosted 10811. It is boosted to allow them to 
hit a spec of -40C on the unit. At the time it was
designed, there was talk about mounting these things in un-heated boxes 
outdoors. After they got a bit further into all the 
details of the designs … that part went away. The spec still hung around long 
enough to apply to very early designs. 

The net result is that you can pretty much destroy the outer heater stuff and 
the oscillator will work fine. There is no need 
for it in a typical lab. There are some alarm triggers that need to be wired 
“ok” when you do so. The details are in the archives. 

But …

Best guess if your unit is at max EFC = the “real” heater on the 10811 has quit 
working. To get at that, you will need to dig 
into the guts of the unit. Given the massive EFC on the Z3801 version of the 
oscillator, it would take a crazy amount of aging
to hit limit.

Bob


> On Mar 3, 2018, at 1:37 PM, Tom Curlee <tcur...@sbcglobal.net> wrote:
> 
> Since the Z3801A is being discussed, I thought I'd ask about an issue I'm 
> having with my unit.  I use my Z3801 as my working lab standard for the usual 
> pieces of RF test equipment.  In the past year or so I've had the unit drop 
> out of lock and go into standby mode.  Resetting/cycling power would bring it 
> back into lock for a while, but it generally got worse and now stays in hold 
> over mode.  LH (thanks Mark Sims!!) reports that everything is operating 
> normally except that the it has a PLL unlock.  The one highly suspicious item 
> is that the DAC is at 99.996902% - full output.
> The unit shows it has over 94.5K hours run time, so I suspect that the OCXO 
> has aged to the point that the EFC can't pull it into lock.  I disassembled 
> the OCXO to see if it had a trimmer capacitor like the standard 10811 units.  
> After removing the outer case and foam insulation, I see that the outer 
> heater is one of the thin printed circuit serpentine heaters on what I think 
> is Kapton.  That would need to be peeled off of the case to either get to the 
> hole for the trimmer (if there is one) or to remove the cover for the inner 
> case.
> What I don't understand is the purpose of what looks like another coil or 
> heater wrapped around the Kapton printed circuit heater stuck to the inner 
> case.  This second coil/heater is 2 layers of 1/8" thick red foam wrapped 
> completely around the inner case, with fine copper wires wrapped over each 
> layer.  At least I think there are wires on each layer.  This whole second 
> heater is taped down and I don't want to dig any further until I know a bit 
> more about what I'm doing or find that there isn't a trimmer on the double 
> oven 10811 oscillators.
> Any ideas on the purpose of the outer heater (or whatever it is)?  Does the 
> double oven 10811 have a manual trimmer that I can adjust to bring the 
> oscillator back to the center of the EFC range?  Assuming that I can manually 
> adjust the OCXO back into adjustment range, will there be any issues with the 
> Z3801 performance, things like phase noise, short term stability, etc?
> An

Re: [time-nuts] Z3801A OCXO manual trimming

[Ed Palmer]

On 2018-03-03 3:56 PM, Tom Curlee wrote:


What I don't understand is the purpose of what looks like another coil or heater 
wrapped around the Kapton printed circuit heater stuck to the inner case.  This 
second coil/heater is 2 layers of 1/8" thick red foam wrapped completely around 
the inner case, with fine copper wires wrapped over each layer.  At least I think 
there are wires on each layer.  This whole second heater is taped down and I don't 
want to dig any further until I know a bit more about what I'm doing or find that 
there isn't a trimmer on the double oven 10811 oscillators.


You might want to read the tear-down info here: 
http://www.realhamradio.com/GPS-oven-journey.htm .  The author suggests 
that this strange structure isn't a heater, but is just a way to 
thermally isolate the inside from the outside.  Seems a bit extreme, but 
HP sometimes did things like that.  Note that right at the bottom of the 
page, there's a link to another article where the fault is diagnosed and 
repaired.



Any ideas on the purpose of the outer heater (or whatever it is)?  Does the 
double oven 10811 have a manual trimmer that I can adjust to bring the 
oscillator back to the center of the EFC range?


According to the tear-down, yes it does.


Assuming that I can manually adjust the OCXO back into adjustment range, will 
there be any issues with the Z3801 performance, things like phase noise, short 
term stability, etc?


AFAIK, it's just a 10811 with extended EFC range, so I don't see why 
tweaking the tuning would compromise anything.


Ed

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Re: [time-nuts] Z3801A OCXO manual trimming

[Bob kb8tq]

Hi

First off some basics about OCXO’s.

In a single oven design, you have a heater that warms up the entire crystal and 
the guts of the oscillator. It is on all the time and 
it gets things up to a temperature that makes sense for a given crystal. It can 
be adjusted based on manufacturing data or by 
trial and error to match the characteristics of that crystal. 

In a double oven design, you have two ovens that are on all the time. One heats 
up the other one. They both work together to
achieve the end result. The gain of one adds to the gain of the other to give 
an improved result. On some double ovens, the 
entire heat range of the inner oven is only 10’s of degrees ….

In a boosted oven, you have a second heater to get things going when it is very 
cold. This is an unusual approach and rarely 
seen. Its normally easier to just design a bit more power into the main oven 
circuit. In a boosted design, the boost heat goes
away in normal operation at typical temperatures. In normal operation, the gain 
of the boost circuit does not count. 

SO ….

The oscillator in the Z3801 is a boosted 10811. It is boosted to allow them to 
hit a spec of -40C on the unit. At the time it was
designed, there was talk about mounting these things in un-heated boxes 
outdoors. After they got a bit further into all the 
details of the designs … that part went away. The spec still hung around long 
enough to apply to very early designs. 

The net result is that you can pretty much destroy the outer heater stuff and 
the oscillator will work fine. There is no need 
for it in a typical lab. There are some alarm triggers that need to be wired 
“ok” when you do so. The details are in the archives. 

But …

Best guess if your unit is at max EFC = the “real” heater on the 10811 has quit 
working. To get at that, you will need to dig 
into the guts of the unit. Given the massive EFC on the Z3801 version of the 
oscillator, it would take a crazy amount of aging
to hit limit.

Bob


> On Mar 3, 2018, at 1:37 PM, Tom Curlee  wrote:
> 
> Since the Z3801A is being discussed, I thought I'd ask about an issue I'm 
> having with my unit.  I use my Z3801 as my working lab standard for the usual 
> pieces of RF test equipment.  In the past year or so I've had the unit drop 
> out of lock and go into standby mode.  Resetting/cycling power would bring it 
> back into lock for a while, but it generally got worse and now stays in hold 
> over mode.  LH (thanks Mark Sims!!) reports that everything is operating 
> normally except that the it has a PLL unlock.  The one highly suspicious item 
> is that the DAC is at 99.996902% - full output.
> The unit shows it has over 94.5K hours run time, so I suspect that the OCXO 
> has aged to the point that the EFC can't pull it into lock.  I disassembled 
> the OCXO to see if it had a trimmer capacitor like the standard 10811 units.  
> After removing the outer case and foam insulation, I see that the outer 
> heater is one of the thin printed circuit serpentine heaters on what I think 
> is Kapton.  That would need to be peeled off of the case to either get to the 
> hole for the trimmer (if there is one) or to remove the cover for the inner 
> case.
> What I don't understand is the purpose of what looks like another coil or 
> heater wrapped around the Kapton printed circuit heater stuck to the inner 
> case.  This second coil/heater is 2 layers of 1/8" thick red foam wrapped 
> completely around the inner case, with fine copper wires wrapped over each 
> layer.  At least I think there are wires on each layer.  This whole second 
> heater is taped down and I don't want to dig any further until I know a bit 
> more about what I'm doing or find that there isn't a trimmer on the double 
> oven 10811 oscillators.
> Any ideas on the purpose of the outer heater (or whatever it is)?  Does the 
> double oven 10811 have a manual trimmer that I can adjust to bring the 
> oscillator back to the center of the EFC range?  Assuming that I can manually 
> adjust the OCXO back into adjustment range, will there be any issues with the 
> Z3801 performance, things like phase noise, short term stability, etc?
> Any suggestions will be most appreciated.
> Thanks,
> Tom
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[time-nuts] Z3801A OCXO manual trimming

[Tom Curlee]

Since the Z3801A is being discussed, I thought I'd ask about an issue I'm 
having with my unit.  I use my Z3801 as my working lab standard for the usual 
pieces of RF test equipment.  In the past year or so I've had the unit drop out 
of lock and go into standby mode.  Resetting/cycling power would bring it back 
into lock for a while, but it generally got worse and now stays in hold over 
mode.  LH (thanks Mark Sims!!) reports that everything is operating normally 
except that the it has a PLL unlock.  The one highly suspicious item is that 
the DAC is at 99.996902% - full output.
The unit shows it has over 94.5K hours run time, so I suspect that the OCXO has 
aged to the point that the EFC can't pull it into lock.  I disassembled the 
OCXO to see if it had a trimmer capacitor like the standard 10811 units.  After 
removing the outer case and foam insulation, I see that the outer heater is one 
of the thin printed circuit serpentine heaters on what I think is Kapton.  That 
would need to be peeled off of the case to either get to the hole for the 
trimmer (if there is one) or to remove the cover for the inner case.
What I don't understand is the purpose of what looks like another coil or 
heater wrapped around the Kapton printed circuit heater stuck to the inner 
case.  This second coil/heater is 2 layers of 1/8" thick red foam wrapped 
completely around the inner case, with fine copper wires wrapped over each 
layer.  At least I think there are wires on each layer.  This whole second 
heater is taped down and I don't want to dig any further until I know a bit 
more about what I'm doing or find that there isn't a trimmer on the double oven 
10811 oscillators.
Any ideas on the purpose of the outer heater (or whatever it is)?  Does the 
double oven 10811 have a manual trimmer that I can adjust to bring the 
oscillator back to the center of the EFC range?  Assuming that I can manually 
adjust the OCXO back into adjustment range, will there be any issues with the 
Z3801 performance, things like phase noise, short term stability, etc?
Any suggestions will be most appreciated.
Thanks,
Tom
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