Re: [time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad?

[Bob Camp]

Hi

If the part is 50 years old that pre-dates the invention of the SC cut. AFIK, 
all of the 
QK glass bottle crystals date to the “pre SC” era. The BT is about the only 
other 
alternative from that era. HP made it their “goto cut” for OCXO’s back then. 
Others
may have followed along ….

Bob
 
> On Nov 21, 2016, at 7:00 PM, Azelio Boriani  wrote:
> 
> A comparison between AT and SC cuts' temperature stability can be found here:
> 
> 
> 
> On Mon, Nov 21, 2016 at 4:21 AM, Bob Camp  wrote:
>> Hi
>> 
>> If the frequency drops as the oven warms up, you have an AT cut crystal. If
>> the frequency goes up as the oven warms up, you have a BT cut crystal. With 
>> an
>> AT or a BT, the frequency change between room and “hot” will depend a lot on
>> the details of the proper oven temperature. A frequency shift of 20 to 40 
>> ppm is not
>> at all unusual as the oven warms up. The oscillator will only tune on 
>> frequency
>> once the oven is hot.
>> 
>> http://www.aextal.com/tutorial-frequency-stability.htm
>> 
>> Regardless of which cut you have (an AT is the best guess). The oven 
>> temperature
>> would be adjusted to put the crystal at it’s minimum sensitivity point. For 
>> an AT that
>> is the lowest frequency. If the oven is not heating to the correct 
>> temperature, you will
>> probably be unable to get the oscillator on frequency.
>> 
>> If there is a circuit problem, the most likely culprit are the inductors. 
>> They form tuned
>> traps that put the circuit onto the correct overtone. This increases the 
>> circuit’s sensitivity
>> to changes in inductance. 50 year old inductors may have been made with core 
>> materials
>> that aged more than just a little bit. I have empirical data on this :)
>> 
>> As others have suggested, check the oven heater along with the oscillator 
>> circuit. The
>> issues you see might come from either one.
>> 
>> Bob
>> 
>>> On Nov 20, 2016, at 6:49 PM, Michael Ulbrich  wrote:
>>> 
>>> Hi there,
>>> 
>>> I'm new to this list and have some interest in quartz crystal and
>>> rubidium oscillators - GPS, NTP, PPS and "clock watching" in general ;-)
>>> 
>>> I snatched an R XSD frequency standard accompanied by an XKE frequency
>>> controller. Found the manuals on KO4BB's site (Thanks a lot for that!
>>> BTW there's a slight mix-up of pages in that some of the XKE pages have
>>> found their way into the XSD manual).
>>> 
>>> My initial hope of a quick and easy restoration project faded a bit when
>>> I looked at the XSD output frequency after heating up the oven. It was
>>> off by about -1 * 10-5 and after cranking the fine tuning for some time
>>> and having another look at the specs I realized that the frequency was
>>> too far off to be dialed in by the fine tuning which only covers about
>>> +/- 2 * 10-7.
>>> 
>>> Next step was to take apart the oven and check series capacitor,
>>> oscillator and the crystal itself. I found that even the coarse
>>> adjustment range of the cylindrical series capacitor (40 - 110 pF) would
>>> not allow to pull the crystal to it's specified frequency. When
>>> replacing the series cap by a ceramic and lowering the value to just
>>> before the oscillation breaks down (about 10 pF) I managed to set the
>>> oscillator frequency offset to  +2.5 * 10-6 at room temperature. But
>>> even this will not suffice when taking into account that the frequency
>>> will drop by a few parts in 10-5 (cf. XSD manual) when the oven heats up
>>> to its operating temperature. I also checked some of the components on
>>> the oscillator PCB which might have an influence on frequency but could
>>> not find any fault.
>>> 
>>> The crystal itself is a disk of about 30 mm diameter mounted in a sealed
>>> glass cylinder of about 38 mm dia. and 43 mm height. There is no socket
>>> just 2 bare wires.. It does not show any visual signs of damage.
>>> According to a reference given in the R XSD manual the crystal's
>>> construction follows a publication from A.W. Warner "Design and
>>> Performance of Ultraprecise 2.5-mc Quartz Crystal Units" in Vol 39,
>>> Issue 5 of Bell Labs Technical Journal (Sept. 1960). According to that
>>> it is an AT-cut 5th overtone design.
>>> 
>>> Now my questions:
>>> 
>>> a) Considering that this gear is about 50 years old, a "crystal gone
>>> bad" situation shouldn't be that much of a surprise, right?  But could
>>> there be any other cause of the "huge" frequency offset besides a bad
>>> crystal? I would very much appreciate any idea that I could try to get
>>> this baby back on spec.
>>> 
>>> b) if nothing else helps: Could any of you give me a hint about who
>>> might be able to supply a spare crystal? I tried my directly reachable
>>> contacts but unfortunately to no avail so far. Please consider that
>>> similar crystals might also have found their way into other
>>> manufacturer's constructions from that era - Sulzer, Racal, HP 

Re: [time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad?

[Bob Camp]

Hi

Thanks for the pictures !!!

Another possible thing to watch for: It may take a *long* time for the oven to 
stabilize at the correct temperature. 

Bob

> On Nov 21, 2016, at 6:31 PM, Michael Ulbrich  wrote:
> 
> Hi all,
> 
> thanks a lot for your helpful suggestions and pointers to sources of
> additional information.
> 
> I also got a few replies off list and one list member may actually have
> a spare crystal!
> 
> Will report to the list as this project (hopefully) progresses.
> 
> BTW what is the "attachment policy" of this list? I will try to attach 2
> - small - images of the crystal (side and top view) and see if they get
> through somehow.
> 
> Thanks again ... Michael
> 
> 
> 
> ___
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Re: [time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad?

[Azelio Boriani]

A comparison between AT and SC cuts' temperature stability can be found here:



On Mon, Nov 21, 2016 at 4:21 AM, Bob Camp  wrote:
> Hi
>
> If the frequency drops as the oven warms up, you have an AT cut crystal. If
> the frequency goes up as the oven warms up, you have a BT cut crystal. With an
> AT or a BT, the frequency change between room and “hot” will depend a lot on
> the details of the proper oven temperature. A frequency shift of 20 to 40 ppm 
> is not
> at all unusual as the oven warms up. The oscillator will only tune on 
> frequency
> once the oven is hot.
>
> http://www.aextal.com/tutorial-frequency-stability.htm
>
> Regardless of which cut you have (an AT is the best guess). The oven 
> temperature
> would be adjusted to put the crystal at it’s minimum sensitivity point. For 
> an AT that
> is the lowest frequency. If the oven is not heating to the correct 
> temperature, you will
> probably be unable to get the oscillator on frequency.
>
> If there is a circuit problem, the most likely culprit are the inductors. 
> They form tuned
> traps that put the circuit onto the correct overtone. This increases the 
> circuit’s sensitivity
> to changes in inductance. 50 year old inductors may have been made with core 
> materials
> that aged more than just a little bit. I have empirical data on this :)
>
> As others have suggested, check the oven heater along with the oscillator 
> circuit. The
> issues you see might come from either one.
>
> Bob
>
>> On Nov 20, 2016, at 6:49 PM, Michael Ulbrich  wrote:
>>
>> Hi there,
>>
>> I'm new to this list and have some interest in quartz crystal and
>> rubidium oscillators - GPS, NTP, PPS and "clock watching" in general ;-)
>>
>> I snatched an R XSD frequency standard accompanied by an XKE frequency
>> controller. Found the manuals on KO4BB's site (Thanks a lot for that!
>> BTW there's a slight mix-up of pages in that some of the XKE pages have
>> found their way into the XSD manual).
>>
>> My initial hope of a quick and easy restoration project faded a bit when
>> I looked at the XSD output frequency after heating up the oven. It was
>> off by about -1 * 10-5 and after cranking the fine tuning for some time
>> and having another look at the specs I realized that the frequency was
>> too far off to be dialed in by the fine tuning which only covers about
>> +/- 2 * 10-7.
>>
>> Next step was to take apart the oven and check series capacitor,
>> oscillator and the crystal itself. I found that even the coarse
>> adjustment range of the cylindrical series capacitor (40 - 110 pF) would
>> not allow to pull the crystal to it's specified frequency. When
>> replacing the series cap by a ceramic and lowering the value to just
>> before the oscillation breaks down (about 10 pF) I managed to set the
>> oscillator frequency offset to  +2.5 * 10-6 at room temperature. But
>> even this will not suffice when taking into account that the frequency
>> will drop by a few parts in 10-5 (cf. XSD manual) when the oven heats up
>> to its operating temperature. I also checked some of the components on
>> the oscillator PCB which might have an influence on frequency but could
>> not find any fault.
>>
>> The crystal itself is a disk of about 30 mm diameter mounted in a sealed
>> glass cylinder of about 38 mm dia. and 43 mm height. There is no socket
>> just 2 bare wires.. It does not show any visual signs of damage.
>> According to a reference given in the R XSD manual the crystal's
>> construction follows a publication from A.W. Warner "Design and
>> Performance of Ultraprecise 2.5-mc Quartz Crystal Units" in Vol 39,
>> Issue 5 of Bell Labs Technical Journal (Sept. 1960). According to that
>> it is an AT-cut 5th overtone design.
>>
>> Now my questions:
>>
>> a) Considering that this gear is about 50 years old, a "crystal gone
>> bad" situation shouldn't be that much of a surprise, right?  But could
>> there be any other cause of the "huge" frequency offset besides a bad
>> crystal? I would very much appreciate any idea that I could try to get
>> this baby back on spec.
>>
>> b) if nothing else helps: Could any of you give me a hint about who
>> might be able to supply a spare crystal? I tried my directly reachable
>> contacts but unfortunately to no avail so far. Please consider that
>> similar crystals might also have found their way into other
>> manufacturer's constructions from that era - Sulzer, Racal, HP ... you
>> name it ...
>>
>> Many thanks in advance!
>>
>> Best regards ... Michael U.
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
> ___
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> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the 

Re: [time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad?

[Alexander Pummer]

"that should cause lowering the frequency" and it will lower the Q of 
the crystal too, therefore it will need more drive!


73

KJ6UHN

Alex


On 11/20/2016 5:00 PM, Alan Melia wrote:
Michael a couple of wild thoughts, make sure there is no 500kHz there 
(this is the crystal fundamental and the maintaining circuit should be 
degenerative there. (Is it a Meecham Bridge?)


That sounds like a baseless IO GT valve (tube in US ) enclosure which 
was probably originally evacuatedhas the vacuum gone soft in 50 
years?I dont know how you would check, but I think that would 
cause a lowering of the frequency.


Alan
G3NYK

- Original Message - From: "Michael Ulbrich" <m...@rentapacs.de>
To: "Time-Nuts" <time-nuts@febo.com>
Sent: Sunday, November 20, 2016 11:49 PM
Subject: [time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad?



Hi there,

I'm new to this list and have some interest in quartz crystal and
rubidium oscillators - GPS, NTP, PPS and "clock watching" in general ;-)

I snatched an R XSD frequency standard accompanied by an XKE frequency
controller. Found the manuals on KO4BB's site (Thanks a lot for that!
BTW there's a slight mix-up of pages in that some of the XKE pages have
found their way into the XSD manual).

My initial hope of a quick and easy restoration project faded a bit when
I looked at the XSD output frequency after heating up the oven. It was
off by about -1 * 10-5 and after cranking the fine tuning for some time
and having another look at the specs I realized that the frequency was
too far off to be dialed in by the fine tuning which only covers about
+/- 2 * 10-7.

Next step was to take apart the oven and check series capacitor,
oscillator and the crystal itself. I found that even the coarse
adjustment range of the cylindrical series capacitor (40 - 110 pF) would
not allow to pull the crystal to it's specified frequency. When
replacing the series cap by a ceramic and lowering the value to just
before the oscillation breaks down (about 10 pF) I managed to set the
oscillator frequency offset to  +2.5 * 10-6 at room temperature. But
even this will not suffice when taking into account that the frequency
will drop by a few parts in 10-5 (cf. XSD manual) when the oven heats up
to its operating temperature. I also checked some of the components on
the oscillator PCB which might have an influence on frequency but could
not find any fault.

The crystal itself is a disk of about 30 mm diameter mounted in a sealed
glass cylinder of about 38 mm dia. and 43 mm height. There is no socket
just 2 bare wires.. It does not show any visual signs of damage.
According to a reference given in the R XSD manual the crystal's
construction follows a publication from A.W. Warner "Design and
Performance of Ultraprecise 2.5-mc Quartz Crystal Units" in Vol 39,
Issue 5 of Bell Labs Technical Journal (Sept. 1960). According to that
it is an AT-cut 5th overtone design.

Now my questions:

a) Considering that this gear is about 50 years old, a "crystal gone
bad" situation shouldn't be that much of a surprise, right?  But could
there be any other cause of the "huge" frequency offset besides a bad
crystal? I would very much appreciate any idea that I could try to get
this baby back on spec.

b) if nothing else helps: Could any of you give me a hint about who
might be able to supply a spare crystal? I tried my directly reachable
contacts but unfortunately to no avail so far. Please consider that
similar crystals might also have found their way into other
manufacturer's constructions from that era - Sulzer, Racal, HP ... you
name it ...

Many thanks in advance!

Best regards ... Michael U.
___
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-
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2016.0.7859 / Virus Database: 4664/13446 - Release Date: 
11/20/16


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Re: [time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad?

[Bob Camp]

Hi

If the frequency drops as the oven warms up, you have an AT cut crystal. If 
the frequency goes up as the oven warms up, you have a BT cut crystal. With an 
AT or a BT, the frequency change between room and “hot” will depend a lot on 
the details of the proper oven temperature. A frequency shift of 20 to 40 ppm 
is not
at all unusual as the oven warms up. The oscillator will only tune on frequency 
once the oven is hot. 

http://www.aextal.com/tutorial-frequency-stability.htm

Regardless of which cut you have (an AT is the best guess). The oven temperature
would be adjusted to put the crystal at it’s minimum sensitivity point. For an 
AT that
is the lowest frequency. If the oven is not heating to the correct temperature, 
you will
probably be unable to get the oscillator on frequency. 

If there is a circuit problem, the most likely culprit are the inductors. They 
form tuned
traps that put the circuit onto the correct overtone. This increases the 
circuit’s sensitivity 
to changes in inductance. 50 year old inductors may have been made with core 
materials 
that aged more than just a little bit. I have empirical data on this :)

As others have suggested, check the oven heater along with the oscillator 
circuit. The
issues you see might come from either one.

Bob

> On Nov 20, 2016, at 6:49 PM, Michael Ulbrich  wrote:
> 
> Hi there,
> 
> I'm new to this list and have some interest in quartz crystal and
> rubidium oscillators - GPS, NTP, PPS and "clock watching" in general ;-)
> 
> I snatched an R XSD frequency standard accompanied by an XKE frequency
> controller. Found the manuals on KO4BB's site (Thanks a lot for that!
> BTW there's a slight mix-up of pages in that some of the XKE pages have
> found their way into the XSD manual).
> 
> My initial hope of a quick and easy restoration project faded a bit when
> I looked at the XSD output frequency after heating up the oven. It was
> off by about -1 * 10-5 and after cranking the fine tuning for some time
> and having another look at the specs I realized that the frequency was
> too far off to be dialed in by the fine tuning which only covers about
> +/- 2 * 10-7.
> 
> Next step was to take apart the oven and check series capacitor,
> oscillator and the crystal itself. I found that even the coarse
> adjustment range of the cylindrical series capacitor (40 - 110 pF) would
> not allow to pull the crystal to it's specified frequency. When
> replacing the series cap by a ceramic and lowering the value to just
> before the oscillation breaks down (about 10 pF) I managed to set the
> oscillator frequency offset to  +2.5 * 10-6 at room temperature. But
> even this will not suffice when taking into account that the frequency
> will drop by a few parts in 10-5 (cf. XSD manual) when the oven heats up
> to its operating temperature. I also checked some of the components on
> the oscillator PCB which might have an influence on frequency but could
> not find any fault.
> 
> The crystal itself is a disk of about 30 mm diameter mounted in a sealed
> glass cylinder of about 38 mm dia. and 43 mm height. There is no socket
> just 2 bare wires.. It does not show any visual signs of damage.
> According to a reference given in the R XSD manual the crystal's
> construction follows a publication from A.W. Warner "Design and
> Performance of Ultraprecise 2.5-mc Quartz Crystal Units" in Vol 39,
> Issue 5 of Bell Labs Technical Journal (Sept. 1960). According to that
> it is an AT-cut 5th overtone design.
> 
> Now my questions:
> 
> a) Considering that this gear is about 50 years old, a "crystal gone
> bad" situation shouldn't be that much of a surprise, right?  But could
> there be any other cause of the "huge" frequency offset besides a bad
> crystal? I would very much appreciate any idea that I could try to get
> this baby back on spec.
> 
> b) if nothing else helps: Could any of you give me a hint about who
> might be able to supply a spare crystal? I tried my directly reachable
> contacts but unfortunately to no avail so far. Please consider that
> similar crystals might also have found their way into other
> manufacturer's constructions from that era - Sulzer, Racal, HP ... you
> name it ...
> 
> Many thanks in advance!
> 
> Best regards ... Michael U.
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

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Re: [time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad?

[Graham / KE9H]

Is your oven doing what it is supposed to be doing?

Sounds more like an oven problem than a crystal problem.

--- Graham

==

On Sun, Nov 20, 2016 at 7:00 PM, Alan Melia <alan.me...@btinternet.com>
wrote:

> Michael a couple of wild thoughts, make sure there is no 500kHz there
> (this is the crystal fundamental and the maintaining circuit should be
> degenerative there. (Is it a Meecham Bridge?)
>
> That sounds like a baseless IO GT valve (tube in US ) enclosure which was
> probably originally evacuatedhas the vacuum gone soft in 50 years?I
> dont know how you would check, but I think that would cause a lowering of
> the frequency.
>
> Alan
> G3NYK
>
> - Original Message - From: "Michael Ulbrich" <m...@rentapacs.de>
> To: "Time-Nuts" <time-nuts@febo.com>
> Sent: Sunday, November 20, 2016 11:49 PM
> Subject: [time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad?
>
>
>
> Hi there,
>>
>> I'm new to this list and have some interest in quartz crystal and
>> rubidium oscillators - GPS, NTP, PPS and "clock watching" in general ;-)
>>
>> I snatched an R XSD frequency standard accompanied by an XKE frequency
>> controller. Found the manuals on KO4BB's site (Thanks a lot for that!
>> BTW there's a slight mix-up of pages in that some of the XKE pages have
>> found their way into the XSD manual).
>>
>> My initial hope of a quick and easy restoration project faded a bit when
>> I looked at the XSD output frequency after heating up the oven. It was
>> off by about -1 * 10-5 and after cranking the fine tuning for some time
>> and having another look at the specs I realized that the frequency was
>> too far off to be dialed in by the fine tuning which only covers about
>> +/- 2 * 10-7.
>>
>> Next step was to take apart the oven and check series capacitor,
>> oscillator and the crystal itself. I found that even the coarse
>> adjustment range of the cylindrical series capacitor (40 - 110 pF) would
>> not allow to pull the crystal to it's specified frequency. When
>> replacing the series cap by a ceramic and lowering the value to just
>> before the oscillation breaks down (about 10 pF) I managed to set the
>> oscillator frequency offset to  +2.5 * 10-6 at room temperature. But
>> even this will not suffice when taking into account that the frequency
>> will drop by a few parts in 10-5 (cf. XSD manual) when the oven heats up
>> to its operating temperature. I also checked some of the components on
>> the oscillator PCB which might have an influence on frequency but could
>> not find any fault.
>>
>> The crystal itself is a disk of about 30 mm diameter mounted in a sealed
>> glass cylinder of about 38 mm dia. and 43 mm height. There is no socket
>> just 2 bare wires.. It does not show any visual signs of damage.
>> According to a reference given in the R XSD manual the crystal's
>> construction follows a publication from A.W. Warner "Design and
>> Performance of Ultraprecise 2.5-mc Quartz Crystal Units" in Vol 39,
>> Issue 5 of Bell Labs Technical Journal (Sept. 1960). According to that
>> it is an AT-cut 5th overtone design.
>>
>> Now my questions:
>>
>> a) Considering that this gear is about 50 years old, a "crystal gone
>> bad" situation shouldn't be that much of a surprise, right?  But could
>> there be any other cause of the "huge" frequency offset besides a bad
>> crystal? I would very much appreciate any idea that I could try to get
>> this baby back on spec.
>>
>> b) if nothing else helps: Could any of you give me a hint about who
>> might be able to supply a spare crystal? I tried my directly reachable
>> contacts but unfortunately to no avail so far. Please consider that
>> similar crystals might also have found their way into other
>> manufacturer's constructions from that era - Sulzer, Racal, HP ... you
>> name it ...
>>
>> Many thanks in advance!
>>
>> Best regards ... Michael U.
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/m
>> ailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
> ___
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> To unsubscribe, go to https://www.febo.com/cgi-bin/m
> ailman/listinfo/time-nuts
> and follow the instructions there.
>
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Re: [time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad?

[KA2WEU--- via time-nuts]

http://www.classicbroadcast.de/downloads/rohde_XSD.pdf
 
 
Greetings,
 
I am surprised that this is the 2.5 MHz  (XSD)and not the new 5 Mhz  
crystal. XSD2 ) Bernd Neubig , on distribution always has a wealth of  
information 
and part. 
 
There was a later R ( XSD 2 )  5 MHz frequency standard,  interchangeable 
with the XSRM Rb standard..
 
I looked at the Internet but did not find a surplus one . Sorry , Ulrich  
Rohde  N1UL
 
 
In a message dated 11/20/2016 7:05:11 P.M. Eastern Standard Time,  
m...@rentapacs.de writes:

Hi  there,

I'm new to this list and have some interest in quartz crystal  and
rubidium oscillators - GPS, NTP, PPS and "clock watching" in general  ;-)

I snatched an R XSD frequency standard accompanied by an XKE  frequency
controller. Found the manuals on KO4BB's site (Thanks a lot for  that!
BTW there's a slight mix-up of pages in that some of the XKE pages  have
found their way into the XSD manual).

My initial hope of a  quick and easy restoration project faded a bit when
I looked at the XSD  output frequency after heating up the oven. It was
off by about -1 * 10-5  and after cranking the fine tuning for some time
and having another look at  the specs I realized that the frequency was
too far off to be dialed in by  the fine tuning which only covers about
+/- 2 * 10-7.

Next step was  to take apart the oven and check series capacitor,
oscillator and the  crystal itself. I found that even the coarse
adjustment range of the  cylindrical series capacitor (40 - 110 pF) would
not allow to pull the  crystal to it's specified frequency. When
replacing the series cap by a  ceramic and lowering the value to just
before the oscillation breaks down  (about 10 pF) I managed to set the
oscillator frequency offset to   +2.5 * 10-6 at room temperature. But
even this will not suffice when taking  into account that the frequency
will drop by a few parts in 10-5 (cf. XSD  manual) when the oven heats up
to its operating temperature. I also checked  some of the components on
the oscillator PCB which might have an influence  on frequency but could
not find any fault.

The crystal itself is a  disk of about 30 mm diameter mounted in a sealed
glass cylinder of about 38  mm dia. and 43 mm height. There is no socket
just 2 bare wires.. It does  not show any visual signs of damage.
According to a reference given in the  R XSD manual the crystal's
construction follows a publication from  A.W. Warner "Design and
Performance of Ultraprecise 2.5-mc Quartz Crystal  Units" in Vol 39,
Issue 5 of Bell Labs Technical Journal (Sept. 1960).  According to that
it is an AT-cut 5th overtone design.

Now my  questions:

a) Considering that this gear is about 50 years old, a  "crystal gone
bad" situation shouldn't be that much of a surprise,  right?  But could
there be any other cause of the "huge" frequency  offset besides a bad
crystal? I would very much appreciate any idea that I  could try to get
this baby back on spec.

b) if nothing else helps:  Could any of you give me a hint about who
might be able to supply a spare  crystal? I tried my directly reachable
contacts but unfortunately to no  avail so far. Please consider that
similar crystals might also have found  their way into other
manufacturer's constructions from that era - Sulzer,  Racal, HP ... you
name it ...

Many thanks in advance!

Best  regards ... Michael  U.
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Re: [time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad?

[Alan Melia]

Michael a couple of wild thoughts, make sure there is no 500kHz there (this 
is the crystal fundamental and the maintaining circuit should be 
degenerative there. (Is it a Meecham Bridge?)


That sounds like a baseless IO GT valve (tube in US ) enclosure which was 
probably originally evacuatedhas the vacuum gone soft in 50 years?I 
dont know how you would check, but I think that would cause a lowering of 
the frequency.


Alan
G3NYK

- Original Message - 
From: "Michael Ulbrich" <m...@rentapacs.de>

To: "Time-Nuts" <time-nuts@febo.com>
Sent: Sunday, November 20, 2016 11:49 PM
Subject: [time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad?



Hi there,

I'm new to this list and have some interest in quartz crystal and
rubidium oscillators - GPS, NTP, PPS and "clock watching" in general ;-)

I snatched an R XSD frequency standard accompanied by an XKE frequency
controller. Found the manuals on KO4BB's site (Thanks a lot for that!
BTW there's a slight mix-up of pages in that some of the XKE pages have
found their way into the XSD manual).

My initial hope of a quick and easy restoration project faded a bit when
I looked at the XSD output frequency after heating up the oven. It was
off by about -1 * 10-5 and after cranking the fine tuning for some time
and having another look at the specs I realized that the frequency was
too far off to be dialed in by the fine tuning which only covers about
+/- 2 * 10-7.

Next step was to take apart the oven and check series capacitor,
oscillator and the crystal itself. I found that even the coarse
adjustment range of the cylindrical series capacitor (40 - 110 pF) would
not allow to pull the crystal to it's specified frequency. When
replacing the series cap by a ceramic and lowering the value to just
before the oscillation breaks down (about 10 pF) I managed to set the
oscillator frequency offset to  +2.5 * 10-6 at room temperature. But
even this will not suffice when taking into account that the frequency
will drop by a few parts in 10-5 (cf. XSD manual) when the oven heats up
to its operating temperature. I also checked some of the components on
the oscillator PCB which might have an influence on frequency but could
not find any fault.

The crystal itself is a disk of about 30 mm diameter mounted in a sealed
glass cylinder of about 38 mm dia. and 43 mm height. There is no socket
just 2 bare wires.. It does not show any visual signs of damage.
According to a reference given in the R XSD manual the crystal's
construction follows a publication from A.W. Warner "Design and
Performance of Ultraprecise 2.5-mc Quartz Crystal Units" in Vol 39,
Issue 5 of Bell Labs Technical Journal (Sept. 1960). According to that
it is an AT-cut 5th overtone design.

Now my questions:

a) Considering that this gear is about 50 years old, a "crystal gone
bad" situation shouldn't be that much of a surprise, right?  But could
there be any other cause of the "huge" frequency offset besides a bad
crystal? I would very much appreciate any idea that I could try to get
this baby back on spec.

b) if nothing else helps: Could any of you give me a hint about who
might be able to supply a spare crystal? I tried my directly reachable
contacts but unfortunately to no avail so far. Please consider that
similar crystals might also have found their way into other
manufacturer's constructions from that era - Sulzer, Racal, HP ... you
name it ...

Many thanks in advance!

Best regards ... Michael U.
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[time-nuts] Rohde & Schwarz XSD 2.5 MHz crystal gone bad?

[Michael Ulbrich]

Hi there,

I'm new to this list and have some interest in quartz crystal and
rubidium oscillators - GPS, NTP, PPS and "clock watching" in general ;-)

I snatched an R XSD frequency standard accompanied by an XKE frequency
controller. Found the manuals on KO4BB's site (Thanks a lot for that!
BTW there's a slight mix-up of pages in that some of the XKE pages have
found their way into the XSD manual).

My initial hope of a quick and easy restoration project faded a bit when
I looked at the XSD output frequency after heating up the oven. It was
off by about -1 * 10-5 and after cranking the fine tuning for some time
and having another look at the specs I realized that the frequency was
too far off to be dialed in by the fine tuning which only covers about
+/- 2 * 10-7.

Next step was to take apart the oven and check series capacitor,
oscillator and the crystal itself. I found that even the coarse
adjustment range of the cylindrical series capacitor (40 - 110 pF) would
not allow to pull the crystal to it's specified frequency. When
replacing the series cap by a ceramic and lowering the value to just
before the oscillation breaks down (about 10 pF) I managed to set the
oscillator frequency offset to  +2.5 * 10-6 at room temperature. But
even this will not suffice when taking into account that the frequency
will drop by a few parts in 10-5 (cf. XSD manual) when the oven heats up
to its operating temperature. I also checked some of the components on
the oscillator PCB which might have an influence on frequency but could
not find any fault.

The crystal itself is a disk of about 30 mm diameter mounted in a sealed
glass cylinder of about 38 mm dia. and 43 mm height. There is no socket
just 2 bare wires.. It does not show any visual signs of damage.
According to a reference given in the R XSD manual the crystal's
construction follows a publication from A.W. Warner "Design and
Performance of Ultraprecise 2.5-mc Quartz Crystal Units" in Vol 39,
Issue 5 of Bell Labs Technical Journal (Sept. 1960). According to that
it is an AT-cut 5th overtone design.

Now my questions:

a) Considering that this gear is about 50 years old, a "crystal gone
bad" situation shouldn't be that much of a surprise, right?  But could
there be any other cause of the "huge" frequency offset besides a bad
crystal? I would very much appreciate any idea that I could try to get
this baby back on spec.

b) if nothing else helps: Could any of you give me a hint about who
might be able to supply a spare crystal? I tried my directly reachable
contacts but unfortunately to no avail so far. Please consider that
similar crystals might also have found their way into other
manufacturer's constructions from that era - Sulzer, Racal, HP ... you
name it ...

Many thanks in advance!

Best regards ... Michael U.
___
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and follow the instructions there.