[time-nuts] How can I measure GPS Antenna quality?

[Mark Sims]

When I was developing the precision survey code for Lady Heather,  I used a lot 
of antennas.  My definition of antenna quality boiled down to how well the 
results of a 48 hour survey compared to the cm level survey point that I had 
for my antenna position (from a Ashtech Z12 receiver / matched choke ring 
antenna).

One thing you can try is running Lady Heather with various antennas with the 
receiver in 3D positioning mode and enabling the lat/lon "scattergram" display 
(G I command in the next release).  This will produce an X-Y plot of fixes from 
the point when the display was enabled.   Better antennas will produce 
"tighter" scattergrams.

Another thing to try is running Lady Heather's precision survey command.  This 
will display the scattergram and also write all the position fix data to the 
file "lla.lla" that you can process as you see fit.

Also, the next version of Lady Heather can write GPX, XML and KML   format log 
files that have the lat/lon/alt info in them.
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Re: [time-nuts] 53132 replacement fan

[Tom Knox]

Hi John;

The exact part in a 2010 Agilent 53132A is EFB0412MD 12VDC 0.10A Brushless 
motor.

Operating Supply Voltage12 VDC

Airflow7.17 CFM

Speed6300 RPM

Pressure Type5.5 mmAq

Bearing TypeBall

Noise24 dBA

Power Rating0.72 W

Housing MaterialPlastic TypeD

Height40 mmLength40 mm


I have a FBK04F12U

Same exact form factor.

Voltage - Rated 12VDC
 Size / Dimension Square - 40mm L x 40mm H
 Width 20.00mm
 Air Flow 9.2 CFM (0.260m³/min)
 Static Pressure 0.472 in H2O (117.6 Pa)
 Bearing Type Ball
 Fan Type Tubeaxial
 Features -  Noise 42 dB(A)  Power (Watts) 2.04W  RPM 9500 RPM


Please feel free to contact me if you want me to ship one.

Cheers;


Thomas Knox
1-303-554-0307
tom.k...@nist.gov and act...@hotmail.com



From: time-nuts  on behalf of John Ackermann N8UR 

Sent: Sunday, November 20, 2016 12:14 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] 53132 replacement fan

Does anyone have a part number for the 53132 fan (or equivalent)?  Mine
is getting pretty noisy.

Thanks!
John
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Re: [time-nuts] How can I measure GPS Antenna quality?

[Mike Cook]

> Le 21 nov. 2016 à 02:57, Tom Van Baak  a écrit :
> 
> Hi Hal,
> 
> That's a very sensible question. I've often wondered the same, but I'm 
> embarrassed to say I have never done a thorough job with it. You know the 
> constellation repeats approximately every 24 hours so you want your X hours 
> to be a multiple of days.
> 
> Looking at SNR seems obvious and may even be sufficient. Alternatively you 
> could track the deviation of the per-SV timing solutions and draw conclusions 
> from that. I suspect multi-path effects would show up in these residuals more 
> than they would show up with just NSV (number of satellites received) or SNR 
> (signal to noise ratio)
> 
> But in some respects, the bottom line is not NSV or SNR or multi-path or 
> anything like that. What counts is only how well the 1PPS matches a local 
> high-quality time standard (e.g., Cesium or better).
> 
> Another issue is that it's possible that the quality of a set of N antenna 
> would sort differently for you than for me: different latitude, different 
> sky-view, different weather. Some time nuts (not me) get lucky with a 
> perfectly clear 360 degree horizon view.
> 
> I agree that N antennas and N receivers makes the experiment easier, because 
> you might spend as much time validating that a set of receivers are all the 
> same as later comparing various antennas.

Sensible question but not easy to answer directly without a  spectrum analyser 
directly connected. Not having one of those I went the n receivers/ m antenna 
method since all I wanted was to get the best subset from what I had. My 
antenna are of the €5-€25 puck variety and I tested about eight 5V, 5/3V active 
Noname and Trimble antenna with  half a dozen receiver types. I am unlucky in 
having just a north looking sky view and in built up area which gets me 
significant multi path at certain times. So I first of all selected a period 
during the day where all receivers were reporting best SNR and max NSV and most 
stable 1PPS . I then measured the 8 antenna over the same time interval (IIRC 
it was 08h-11h) against the 1PPS of a PRS10 rubidium ref.  The GPS 1PPS was 
verified to see if it held the manufacturers stability spec which they mostly 
did. It was easy to see this against the rubidium signal. So I picked the best 
4 and use them to feed my receiver pen via Mini-Circuits distribut
 ers ( There is a small signal loss here but in spec. 3db IIRC ). They have 
been in place for about 3-4 years at least without issue. 

> 
> With that in mind, consider the slice & dice (chopper) idea -- use a VHF 
> relay switch / mux and round-robin N antenna across N receivers every, say, 
> 10 minutes. That gives you 144 points per receiver / antenna pair per day and 
> avoids the geometry and pre-calibration issues, as well as environment and 
> local reference effects. Rubidium would be sufficient. It's possible the 
> first minute of each segment may be weird (as the receiver switches from lost 
> to lock mode), but you can handle that in your data reduction.
> 
> /tvb
> 
> - Original Message - 
> From: "Hal Murray" 
> To: 
> Cc: "Hal Murray" 
> Sent: Sunday, November 20, 2016 2:13 PM
> Subject: [time-nuts] How can I measure GPS Antenna quality?
> 
> 
>> 
>> Is that even a sensible question?  Is there a better way to phrase it?
>> 
>> 
>> The problem I'm trying to avoid is that the weather and the satellite 
>> geometry change over time so I can't just collect data for X hours, switch 
>> to 
>> the other antenna or move the antenna to another location, collect more 
>> data, 
>> then compare the two chunks of data.
>> 
>> The best I can think of would be to setup a reference system so I can 
>> collect 
>> data from  2 antennas and 2 receivers at the same time.  It would probably 
>> require some preliminary work to calibrate the receivers.  I think I can do 
>> that by swapping the antenna cables.
>> 
>> 
>> If I gave you a pile of data, how would you compute a quality number?  Can I 
>> just sum up the S/N slots for each visible/working satellite?
>> 
>> 
>> -- 
>> These are my opinions.  I hate spam.
>> 
> 
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"The power of accurate observation is commonly called cynicism by those who 
have not got it. »
George Bernard Shaw

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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" 
To: "Time-Nuts" 
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.
> ___
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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 
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" 
> To: "Time-Nuts" 
> 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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Re: [time-nuts] How can I measure GPS Antenna quality?

[Chris Albertson]

If you run two antenna simultaneously then...

1) they both can't be at the same location and
2) What if the two antenna interfere one with the other.

I think maybe you need to collect data over a long enough period of tine
that wether averages out.   the satellite tracks repeate pretty much exactly

What you might want to know about an antenna is more than just S/N for good
locations but how it does with adverse conditions like multi path and a
nearby jammer and maybe gain vs. elevation and also dumb practical stuff
like if birds like to perch on it and if there is a way to route the cable
through the mast pipe or not


On Sun, Nov 20, 2016 at 2:13 PM, Hal Murray  wrote:

>
> Is that even a sensible question?  Is there a better way to phrase it?
>
>
> The problem I'm trying to avoid is that the weather and the satellite
> geometry change over time so I can't just collect data for X hours, switch
> to
> the other antenna or move the antenna to another location, collect more
> data,
> then compare the two chunks of data.
>
> The best I can think of would be to setup a reference system so I can
> collect
> data from  2 antennas and 2 receivers at the same time.  It would probably
> require some preliminary work to calibrate the receivers.  I think I can do
> that by swapping the antenna cables.
>
>
> If I gave you a pile of data, how would you compute a quality number?  Can
> I
> just sum up the S/N slots for each visible/working satellite?
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
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> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] How can I measure GPS Antenna quality?

[Tom Van Baak]

Hi Hal,

That's a very sensible question. I've often wondered the same, but I'm 
embarrassed to say I have never done a thorough job with it. You know the 
constellation repeats approximately every 24 hours so you want your X hours to 
be a multiple of days.

Looking at SNR seems obvious and may even be sufficient. Alternatively you 
could track the deviation of the per-SV timing solutions and draw conclusions 
from that. I suspect multi-path effects would show up in these residuals more 
than they would show up with just NSV (number of satellites received) or SNR 
(signal to noise ratio)

But in some respects, the bottom line is not NSV or SNR or multi-path or 
anything like that. What counts is only how well the 1PPS matches a local 
high-quality time standard (e.g., Cesium or better).

Another issue is that it's possible that the quality of a set of N antenna 
would sort differently for you than for me: different latitude, different 
sky-view, different weather. Some time nuts (not me) get lucky with a perfectly 
clear 360 degree horizon view.

I agree that N antennas and N receivers makes the experiment easier, because 
you might spend as much time validating that a set of receivers are all the 
same as later comparing various antennas.

With that in mind, consider the slice & dice (chopper) idea -- use a VHF relay 
switch / mux and round-robin N antenna across N receivers every, say, 10 
minutes. That gives you 144 points per receiver / antenna pair per day and 
avoids the geometry and pre-calibration issues, as well as environment and 
local reference effects. Rubidium would be sufficient. It's possible the first 
minute of each segment may be weird (as the receiver switches from lost to lock 
mode), but you can handle that in your data reduction.

/tvb

- Original Message - 
From: "Hal Murray" 
To: 
Cc: "Hal Murray" 
Sent: Sunday, November 20, 2016 2:13 PM
Subject: [time-nuts] How can I measure GPS Antenna quality?


> 
> Is that even a sensible question?  Is there a better way to phrase it?
> 
> 
> The problem I'm trying to avoid is that the weather and the satellite 
> geometry change over time so I can't just collect data for X hours, switch to 
> the other antenna or move the antenna to another location, collect more data, 
> then compare the two chunks of data.
> 
> The best I can think of would be to setup a reference system so I can collect 
> data from  2 antennas and 2 receivers at the same time.  It would probably 
> require some preliminary work to calibrate the receivers.  I think I can do 
> that by swapping the antenna cables.
> 
> 
> If I gave you a pile of data, how would you compute a quality number?  Can I 
> just sum up the S/N slots for each visible/working satellite?
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 

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Re: [time-nuts] How can I measure GPS Antenna quality?

[Graham / KE9H]

You need a definition of "Quality" to work with.

One definition might be "does it meet published specs? under what
conditions?"
Another definition might be associated with reliability and ruggedness.
Longevity in outdoor conditions.
Another might be with the antenna supporting your use case.
Another might be with suppression of reflections and spurious signals from
below the horizon.

So, the definition of "Quality" might change drastically with the use case
and from your expectations as to its cost.

If you have a definition of your quality criteria, then this crowd can
probably tell you what to measure and how to analyze the measurement data.

--- Graham

==

On Sun, Nov 20, 2016 at 4:13 PM, Hal Murray  wrote:

>
> Is that even a sensible question?  Is there a better way to phrase it?
>
>
> The problem I'm trying to avoid is that the weather and the satellite
> geometry change over time so I can't just collect data for X hours, switch
> to
> the other antenna or move the antenna to another location, collect more
> data,
> then compare the two chunks of data.
>
> The best I can think of would be to setup a reference system so I can
> collect
> data from  2 antennas and 2 receivers at the same time.  It would probably
> require some preliminary work to calibrate the receivers.  I think I can do
> that by swapping the antenna cables.
>
>
> If I gave you a pile of data, how would you compute a quality number?  Can
> I
> just sum up the S/N slots for each visible/working satellite?
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
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>
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Re: [time-nuts] 53132 replacement fan

[Christopher Hoover]

I was able to cross it easily to a well-known fan manufacturer's part.
If someone doesn't chime in, I'll dig through my notes and get you the
details.

-christopher.
73 de AI6KG

On Sun, Nov 20, 2016 at 11:14 AM, John Ackermann N8UR  wrote:

> Does anyone have a part number for the 53132 fan (or equivalent)?  Mine is
> getting pretty noisy.
>
> Thanks!
> John
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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" 

To: "Time-Nuts" 
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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[time-nuts] How can I measure GPS Antenna quality?

[Hal Murray]

Is that even a sensible question?  Is there a better way to phrase it?


The problem I'm trying to avoid is that the weather and the satellite 
geometry change over time so I can't just collect data for X hours, switch to 
the other antenna or move the antenna to another location, collect more data, 
then compare the two chunks of data.

The best I can think of would be to setup a reference system so I can collect 
data from  2 antennas and 2 receivers at the same time.  It would probably 
require some preliminary work to calibrate the receivers.  I think I can do 
that by swapping the antenna cables.


If I gave you a pile of data, how would you compute a quality number?  Can I 
just sum up the S/N slots for each visible/working satellite?


-- 
These are my opinions.  I hate spam.



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[time-nuts] Nortel GPS hard to hold lock reciently

[Jeff AC0C]

I have a Nortel/Trimble GPSDO which has been holding lock for the last month – 
at least it’s been in lock whenever I have thought to check it.  But it seems 
like for the last several days LH has been indicating “RECOVERY MODE” or “OCXO 
COMP” instead of PHASE LOCKED.  

Appreciate any suggestions.  I really don’t know what I’m looking at with the 
LH screen so the reason for this is likely literally in front of my eyes but I 
just don’t know enough to interpret what I’m seeing.

73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie

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Re: [time-nuts] L1 L2 choke Ring Question

[bg]

Hi,
There is(was) a 26dB lna in that antenna.
--
   Björn

Sent from my smartphone.
 Original message From: Magnus Danielson 
 Date: 20/11/2016  21:42  (GMT+01:00) To: 
time-nuts@febo.com Cc: mag...@rubidium.se Subject: Re: [time-nuts] L1 L2 choke 
Ring Question 
Tom,

If I recall correctly, that antenna element is passive and I expect 
there to be an amplifier there. The antenna element you can find 
separately on ebay.

Cheers,
Magnus

On 11/20/2016 08:48 PM, Tom Knox wrote:
> I recently purchased a used L1 L2 Choke ring antenna AeroAntenna 
> AT2775-20W-000-05-26-NM, it has an AT2775 aircraft antenna with a 3.3" x 1.8" 
> bolt pattern at it's heart.
>
> Sadly the antenna is dead. I have been looking into the possibility of 
> replacing the aircraft antenna portion and was wondering what the critical 
> specs were and the approximate tolerances. I found an antenna from another 
> manufacturer with the exact bolt pattern, but it appears the phase center is 
> 1-2mm lower.
>
> Any thoughts would be greatly appreciated.
>
> Or if anyone has a AeroAntenna AT2775 aircraft antenna with a 3.3" x 1.8" 
> bolt pattern they would be willing to sell or trade contact me off list.
>
> Thanks!
>
>
> Thomas Knox
>
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Re: [time-nuts] L1 L2 choke Ring Question

[Attila Kinali]

On Sun, 20 Nov 2016 19:48:42 +
Tom Knox  wrote:

> I recently purchased a used L1 L2 Choke ring antenna AeroAntenna
> AT2775-20W-000-05-26-NM, it has an AT2775 aircraft antenna with a 3.3" x 
> 1.8" bolt pattern at it's heart.

Do you have pictures of the antenna module?

Have you tried to take it apart?
It is likely to be a standard passive antenna with a simple LNA.
As long as the antenna isn't mechanically damaged, it is likely
that just the LNA is fried (lightning strike?). One should be
able to replace the LNA chip or the whole LNA module.

> Sadly the antenna is dead. I have been looking into the possibility of
> replacing the aircraft antenna portion and was wondering what the critical
> specs were and the approximate tolerances. I found an antenna from another
> manufacturer with the exact bolt pattern, but it appears the phase center is
> 1-2mm lower.
> 
> Any thoughts would be greatly appreciated.

That shouldn't be a problem. The chocke ring acts like an high impedance
area around the antenna. You can see it as an "isolator" or resistor
for electromagnetic waves. I.e. if you are a bit lower, you will get
less from the reflections from the ground and proably have less reception
in the lower elevations. It could be, that an antenna that wasn't designed
for a choke ring will be slightly detuned. But that should pose any problem.
I'd guess the signal los would be minuscule.

 
> Or if anyone has a AeroAntenna AT2775 aircraft antenna with a 3.3" x 1.8" 
> bolt pattern they would be willing to sell or trade contact me off list.

The AT2775 is a whole family of antennas. One would need a bit more information
about which it actually is. They do pop up on ebay from time to time.

Attila Kinali

-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] 53132 replacement fan

[Tom Knox]

Hi John;

There is a good chance I have the exact fan. I will check later today and let 
you know. If I do have it I well send you one. At least I should be able to 
find the Agilent and manufacturer part number .

Cheers;

Thomas Knox
Sr Test and Measurement Engineer
Boulder Colorado 80305
1-303-554-0307
act...@hotmail.com



From: time-nuts  on behalf of John Ackermann N8UR 

Sent: Sunday, November 20, 2016 12:14 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] 53132 replacement fan

Does anyone have a part number for the 53132 fan (or equivalent)?  Mine
is getting pretty noisy.

Thanks!
John
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Enterprises
www.febo.com
time-nuts is a low volume, high SNR list for the discussion of precise time and 
frequency measurement and related topics. To see the collection of prior 
postings to ...


and follow the instructions there.
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Re: [time-nuts] 53132 replacement fan

[Peter Vince]

Hi John,

 I have a copy of the Agilent 53132 components list from 2007, but it
seems to only cover the circuit boards :-(  Anyway, for what its worth, I
have put it in my dropbox as it is a 3.2 megabyte PDF - see:


https://www.dropbox.com/s/f9qd42g6qr5cnhx/HP53132A%20Components%205989-6308EN.pdf?dl=0

I have also put a similar file for the 53131:


https://www.dropbox.com/s/sgp9z9vmmbruelg/HP53131A%20Components%205989-6307EN.pdf?dl=0

  Regards,

Peter


On 20 November 2016 at 19:14, John Ackermann N8UR  wrote:

> Does anyone have a part number for the 53132 fan (or equivalent)?  Mine is
> getting pretty noisy.
>
> Thanks!
> John
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> ailman/listinfo/time-nuts
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>
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Re: [time-nuts] L1 L2 choke Ring Question

[Magnus Danielson]

Tom,

If I recall correctly, that antenna element is passive and I expect 
there to be an amplifier there. The antenna element you can find 
separately on ebay.


Cheers,
Magnus

On 11/20/2016 08:48 PM, Tom Knox wrote:

I recently purchased a used L1 L2 Choke ring antenna AeroAntenna AT2775-20W-000-05-26-NM, 
it has an AT2775 aircraft antenna with a 3.3" x 1.8" bolt pattern at it's heart.

Sadly the antenna is dead. I have been looking into the possibility of 
replacing the aircraft antenna portion and was wondering what the critical 
specs were and the approximate tolerances. I found an antenna from another 
manufacturer with the exact bolt pattern, but it appears the phase center is 
1-2mm lower.

Any thoughts would be greatly appreciated.

Or if anyone has a AeroAntenna AT2775 aircraft antenna with a 3.3" x 1.8" bolt 
pattern they would be willing to sell or trade contact me off list.

Thanks!


Thomas Knox

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[time-nuts] L1 L2 choke Ring Question

[Tom Knox]

I recently purchased a used L1 L2 Choke ring antenna AeroAntenna 
AT2775-20W-000-05-26-NM, it has an AT2775 aircraft antenna with a 3.3" x 1.8" 
bolt pattern at it's heart.

Sadly the antenna is dead. I have been looking into the possibility of 
replacing the aircraft antenna portion and was wondering what the critical 
specs were and the approximate tolerances. I found an antenna from another 
manufacturer with the exact bolt pattern, but it appears the phase center is 
1-2mm lower.

Any thoughts would be greatly appreciated.

Or if anyone has a AeroAntenna AT2775 aircraft antenna with a 3.3" x 1.8" bolt 
pattern they would be willing to sell or trade contact me off list.

Thanks!


Thomas Knox

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[time-nuts] 53132 replacement fan

[John Ackermann N8UR]

Does anyone have a part number for the 53132 fan (or equivalent)?  Mine 
is getting pretty noisy.


Thanks!
John
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Re: [time-nuts] HP 55300A

[Bob Camp]

Hi

At normal room temperatures, you simply can not run enough air past the OCXO
to “cool it to much”. The OCXO heater will simply put out a bit more power as 
you
increase the air flow. That’s not to say that the performance will improve any 
as the
OCXO is quickly following any twitch or bump in the room temperature. 

Bob

> On Nov 20, 2016, at 9:41 AM, Gary Neilson  wrote:
> 
> I recently got a HP55300A on ebay for parts. It works fine but runs on 48V.
> 
> I am going  to install a AC supply inside and also place a fan on the top for 
> cooling.
> 
> I hope the air flow will not cool the OCXO too much.
> 
> I am also looking for documentation. I have the User manual but am looking 
> for the Programming Manual.
> 
> Thanks
> 
> Gary Neilson
> 
> K5DSR
> 
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Re: [time-nuts] Need for a document comparing time interval counters

[Bob Camp]

Hi

Once you get into used gear that is many decades old, the actual performance of 
*your* counter 
is likely to be different than the performance of mine. If you are willing to 
go through all of the 
detailed alignment steps (and possibly replace parts) yours will work better 
than mine. How much
better will be a “that depends” sort of thing. Best guess is quite a bit 
better. 

Even in sparkling new condition with everything working, you still have a very 
basic “are you 
after frequency or after time?” question. The newer counters (I would toss the 
CNT-90 into the 
batch) have various tricks in them to improve frequency estimation. The older 
stuff simply did 
not have the horsepower to do some of this. Time wise some of the older 
counters did pretty well. 

So, is a 53132 worth more than a 5335? Sure it is. Is a 53230 worth more than a 
53132? Yes. 
Are they worth the delta that people charge? That depends a lot on how much 
cash you have
lying around. If you have a $200K lab already and your yearly spend on gear is 
$50K that is very
different than a yearly spend of < $1,000. If you can afford the newer stuff, 
it comes with nice things
like replacement parts / factory repair. On the older gear, purchase of a 
“parts donor” unit may
be the only way to do a repair. 

On the new stuff (as you have already noted) the auction sites may not be your 
best source. The
price Keysight charges for a demo unit *may* be your best deal. A local (= in 
country) equipment 
rental guy might also be a better source. Neither one are likely to give you a 
great deal today. In
both cases it’s a “let them know” sort of thing. You might or might not get a 
call back in the next 
couple of months. 

Lots of issues and not much clarity in terms of do this or do that — sorry !

Bob

> On Nov 19, 2016, at 8:55 PM, Dr. David Kirkby  wrote:
> 
> If anyone has the time & inclination, a document comparing different time 
> interval counters would be useful to budding time nuts. There are quite a few 
> different models at prices that are affordable to many.
> 
> I have had a HP 5370B and a Stanford Research  SR620, but have neither now. I 
> regretted selling the HP, but then after buying the SR620, I swapped that and 
> a 4.2 GHz HP signal generator for an HP 4291B 1.8 GHz impedance and material 
> analyzer. 
> 
> I was looking for something cheap,  but see a used Keysight 53230A on eBay 
> for considerably more than a new one from Keysight. It had a "make offer" so 
> I could not resist pointing out a new one is much less, and making a 
> redicously low offer of $1000. I doubt it will be accepted,  but one never 
> knows.  I once got a current Ketsight product for 2% of the current price,  
> so anything is possible.  
> 
> But a  comparison of TI counters,  and a discussion of the important 
> specifications would be njce. 
> 
> 
> .Dave. 
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[time-nuts] HP 55300A

[Gary Neilson]

I recently got a HP55300A on ebay for parts. It works fine but runs on 48V.

I am going  to install a AC supply inside and also place a fan on the 
top for cooling.


I hope the air flow will not cool the OCXO too much.

I am also looking for documentation. I have the User manual but am 
looking for the Programming Manual.


Thanks

Gary Neilson

K5DSR

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Re: [time-nuts] Inside of FT1200-100

[Charles Steinmetz]

Christopher wrote:


Despite running out the three sloted screws on the "top" around the
circumference,  I'm not into the inside yet.   I don't have the  right
thin-walled socket to remove the nuts at the opposite end.


It looks like a standard 5/32" nut driver will work fine.



Best regards,

Charles



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Re: [time-nuts] Inside of FT1200-100

[J. L. Trantham]

Christopher,

Enjoyed the pictures.

You might want to look at these items on theBay.

381408412092

311736541103

I've had the same issue and broke down and bought a set of these small nut 
drivers.

Good luck.

Joe

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Christopher 
Hoover
Sent: Saturday, November 19, 2016 11:45 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Inside of FT1200-100

tl;dr: I've made some progress and have the1200  oscillator core out of the
dewar:

https://goo.gl/photos/SDHtvgFmftQq6vYJA



I got some 5 thou brass stock and worked it between the rubber sheet and the 
dewar.

That seemed to help but it was insufficient free things up -- I busted off the 
unused solder lug trying to pull the core out with it.

Having not a lot to lose, I took a chance that the screws going into the
TO-23 went into threaded holes (rather than being clearance holes with nuts 
inside).  This was indeed the case.

With two 6-32 threaded rods into the TO-23 threaded holes and and an 
appropriately machined piece of mild steel bar stock suspended across the case 
, I was able to easily get the 
oscillator core out of the dewar by evenly tightening the the nuts on
the bar.Really easily -- I might have been able to pull it out by just
pulling on the bar stock.  I don't know if the shim stock shenanigans were even 
needed.

Despite running out the three sloted screws on the "top" around the
circumference,  I'm not into the inside yet.   I don't have the  right
thin-walled socket to remove the nuts at the opposite end.

I found an epoxy covered hole on the top.   It is/was under the green blob
midway between 1 and 2 o'clock in this picture here 
..  There was something blue and
at this point crumbly underneath it.   Not sure yet what, if anything, is
beyond all of that.  I'm hoping for a trimmer cap.  :-)

-- Christopher.
73 de AI6KG




On Mon, Sep 26, 2016 at 9:24 PM, Chuck Harris  wrote:

> Back when I was going to work on mine, I was thinking of prying the 
> rubber away from the aluminum oven with something like a feeler gauge, 
> but also using some naptha (lighter fluid) to help release any 
> adhesive...  I didn't get around to doing it, but that was the way I 
> was going to progress.
>
> -Chuck Harris
>
> Ed Palmer wrote:
> >
> >
> > On 2016-09-26 10:00 AM, Christopher Hoover  wrote:
> >>> >
> >>> >You might be able to slide something like a feeler guage down 
> >>> >between
> the
> >>> >oven and the rubber blanket to break the oscillator free.  The 
> >>> >oven
> on mine
> >>> >is a plain metal cylinder.  This way, the rubber sheet should 
> >>> >protect
> the
> >>> >Dewar from your feeler guage.  On mine, the mounting bolts for 
> >>> >the
> 2N3792
> >>> >transistor both have ground lugs.  I think I see them on yours.  
> >>> >You
> could
> >>> >hook something through the ground lugs and use that to pull the
> oscillator
> >>> >out of the rubber sheet and then remove the sheet later.
> >>> >
> >> Thanks Ed,
> >>
> >> I think the rubber sheet on mine is against metal.  I haven't yet 
> >> seen
> the
> >> glass dewar.
> >>
> >> The adhesion is huge.
> >>
> >> Do you know if the holes opposite the 2N3792 are threaded?   If they
> are, I
> >> might try running the screws out and using those holes with longer
> screws
> >> as my pull points.I can't pull on the lugs hard enough -- I've
> tried.
> >>
> >> -christopher.
> >> 73 de AI6KG
> >
> > Yes, you have seen the Dewar.  The silvery ring that's outside the
> rubber is the top
> > of the Dewar.  What you have to do is unstick and unfold the rubber
> starting from the
> > open area in the center.  Work your way outward.  The rubber is only 
> > 2
> or 3 mm
> > thick.  Once you completely clear the rubber out of the way, you'll 
> > see
> the edge of
> > the oven.  The TO-3 transistor is mounted on top of the oven assembly.
> Once you can
> > see the edge, you have to slide something like a long feeler gauge 
> > down
> along the
> > edge of the oven to break it free from the rubber.  Work your way 
> > all
> around the
> > oven.  It's about 85 mm long.  It'll still be stuck on the bottom, 
> > but
> you might be
> > able to pull it free.
> >
> > When I took mine apart, I ended up tearing off all the rubber at the 
> > top
> and then
> > cutting out that ring of hard foam to get at the Dewar so I could 
> > smash
> it more.  I'm
> > guessing you'd rather not do that! :)  But sacrificing the rubber on 
> > the
> top might be
> > okay, if you have to.
> >
> > Sorry, but I don't know if the mounting holes for the transistor are
> threaded or
> > not.  In any case, since the oven and Dewar are bonded to the 
> > rubber,
> you're pulling
> > on the Dewar when you pull on the oven.  Not a good plan until you 
> > break
> the oven
> > free from the