Re: [time-nuts] How to get unknown frequency quartz crystals oscillating

[Bob Camp]

Hi

The original question related to crystals that ran down into the 10’s of KHz 
range. For those, a
high resistance is not unreasonable at all. For more “normal” AT cut resonators 
in “big" packages
it is not unreasonable to expect the resistance on the fundamental to be 
approximately the same 
as the frequency in MHz. As the overtone goes up, it is not unusual for the 
resistance to go up
as the overtone number. There are an almost infinite number of qualifiers on 
all of that. 

The range of crystal resistance between things like 3 MHz AT’s and 32 KHz watch 
crystals is one
of the things that makes building an one size fits all oscillator difficult. 

Bob


> On Jun 5, 2016, at 9:04 AM, Tim Shoppa  wrote:
> 
> Bob -
> 
>  Crystal resistance of 100K probably applies to the large low frequency
> crystals. Modern HF fundamental crystals tend to be around 50 ohms at their
> fundamental and I think higher for overtone crystals. Older crystals in the
> HF range in the FT-247 holders seem to usually be several hundred ohms.
> 
>  I've certainly swept crystals before to look for spurs, but I usually use
> small sweep ranges like a few hundred Hz around where I know the spur to be
> anyway. This is kinda like the drunk light only looking under the
> streetlights for his keys because he knows he'll never find them if they're
> anywhere else. Not to sound too pessimistic but when applying this to
> crystals from the 50's it seemed like it was a lot easier to find the spurs
> than the fundamental!
> 
> Tim N3QE
> 
> On Sat, Jun 4, 2016 at 8:29 AM, Bob Camp  wrote:
> 
>> Hi
>> 
>> Simple approach is to assume that you have a crystal resistance in the
>> range of 100K ohms. If you guess to
>> high, the oscillator will just work to well :)
>> 
>> Multiple JFETS in cascade for the higher frequency stuff should work. For
>> anything below 20 KHz, an op-amp
>> is likely your best bet.
>> 
>> A spectrum analyzer with a tracking generator will give you some idea of
>> their impedance and *if* they still have
>> any activity at all.
>> 
>> Bob
>> 
>>> On Jun 4, 2016, at 4:46 AM, Mike Cook  wrote:
>>> 
>>> Hi,
>>> 
>>> I have a number of crystals either in glass, bakelite, ceramic or metal
>> housings that I would like to get resonating . They are of three basic
>> types.
>>> Square, or rectangular flat
>>> Round flat
>>> Bar  square section
>>> Sizes range from 2-10cm or more in the longest face.
>>> 
>>> Some have frequency markings. ranging from IKHz 5MHz.
>>> Others have none.
>>> Some are of  Military origin, probably radios and as they have markings
>> I can probably find a schematic from the radios to see how to proceed.
>> There may be dedicated testers still around. I am not so interested in this
>> bunch at the moment.
>>> Others have no known origin so I have no idea what oscillator circuits
>> were used with them.
>>> In terms of vintage, I would guess pre 1940  to late 50s
>>> 
>>> I have built a little Pierce circuit an tried a few. Some of the later
>> 1-5MHz crystals will oscillate but there are a lot of parasitic signals as
>> well as the supposed fundamental. I cannot make any of the low frequency /
>> big crystals to react.
>>> 
>>> So my question:
>>> If you had a crystal with unknown frequency and drive requirements that
>> you wanted to investigate. How would you go about it?
>>> 
>>> If I can get them going I will share the Adevs. I don’t have a spectrum
>> analyser so I can’t do phase noise.
>>> 
>>> Regards
>>> 
>>> "The power of accurate observation is commonly called cynicism by those
>> who have not got it. »
>>> George Bernard Shaw
>>> 
>>> ___
>>> 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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>> and follow the instructions there.
>> 
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Re: [time-nuts] How to get unknown frequency quartz crystals oscillating

[Tim Shoppa]

Bob -

  Crystal resistance of 100K probably applies to the large low frequency
crystals. Modern HF fundamental crystals tend to be around 50 ohms at their
fundamental and I think higher for overtone crystals. Older crystals in the
HF range in the FT-247 holders seem to usually be several hundred ohms.

  I've certainly swept crystals before to look for spurs, but I usually use
small sweep ranges like a few hundred Hz around where I know the spur to be
anyway. This is kinda like the drunk light only looking under the
streetlights for his keys because he knows he'll never find them if they're
anywhere else. Not to sound too pessimistic but when applying this to
crystals from the 50's it seemed like it was a lot easier to find the spurs
than the fundamental!

Tim N3QE

On Sat, Jun 4, 2016 at 8:29 AM, Bob Camp  wrote:

> Hi
>
> Simple approach is to assume that you have a crystal resistance in the
> range of 100K ohms. If you guess to
> high, the oscillator will just work to well :)
>
> Multiple JFETS in cascade for the higher frequency stuff should work. For
> anything below 20 KHz, an op-amp
> is likely your best bet.
>
> A spectrum analyzer with a tracking generator will give you some idea of
> their impedance and *if* they still have
> any activity at all.
>
> Bob
>
> > On Jun 4, 2016, at 4:46 AM, Mike Cook  wrote:
> >
> > Hi,
> >
> > I have a number of crystals either in glass, bakelite, ceramic or metal
> housings that I would like to get resonating . They are of three basic
> types.
> > Square, or rectangular flat
> > Round flat
> > Bar  square section
> > Sizes range from 2-10cm or more in the longest face.
> >
> > Some have frequency markings. ranging from IKHz 5MHz.
> > Others have none.
> > Some are of  Military origin, probably radios and as they have markings
> I can probably find a schematic from the radios to see how to proceed.
> There may be dedicated testers still around. I am not so interested in this
> bunch at the moment.
> > Others have no known origin so I have no idea what oscillator circuits
> were used with them.
> > In terms of vintage, I would guess pre 1940  to late 50s
> >
> > I have built a little Pierce circuit an tried a few. Some of the later
> 1-5MHz crystals will oscillate but there are a lot of parasitic signals as
> well as the supposed fundamental. I cannot make any of the low frequency /
> big crystals to react.
> >
> > So my question:
> > If you had a crystal with unknown frequency and drive requirements that
> you wanted to investigate. How would you go about it?
> >
> > If I can get them going I will share the Adevs. I don’t have a spectrum
> analyser so I can’t do phase noise.
> >
> > Regards
> >
> > "The power of accurate observation is commonly called cynicism by those
> who have not got it. »
> > George Bernard Shaw
> >
> > ___
> > 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] How to get unknown frequency quartz crystals oscillating

[Azelio Boriani]

In the July/August 2008 QEX magazine there is an article by VE5FP
"Some Thoughts On Crystal Parameter Measurement" that may be of
interest.

On Sat, Jun 4, 2016 at 11:01 PM, Bob Camp  wrote:
> Hi
>
> There are two things you may be talking about:
>
> 1) The pressure springs on things like FT-243 holders, they are generic 
> springs.
>
> 2) The connection leads on plated blanks, they are indeed strange *and* 
> soldering to the blank is a big problem.
>
> I’m guessing you are in bucket number 2.
>
> Bob
>
>
>> On Jun 4, 2016, at 1:41 PM, Mike Cook  wrote:
>>
>> Thanks all for your advice, hints, tips and links. Lots to read , do and 
>> some hardware to check.  I don’t have a frequency generator so I’ll have to 
>> go another route.
>>
>> Oh. One last Q. Has anyone tried repairing the « spring » wire electric 
>> connections on large quartz plates. In one large unit I have they had 
>> corroded and dropped the plate, luckily no damage.  I have done one, but I 
>> have no Idea what the original wire composition was so have certainly 
>> induced some stray capacitance/resistance. It is possible that it was a 
>> filter rather than a frequency source as it was not in a vacuum.
>>
>> Have a good one.
>>
>>> Le 4 juin 2016 à 18:49, Bernd Neubig  a écrit :
>>>
>>>
>>> Tim Shoppa wrote:
 The Pierce logic-gate-biased-active oscillator is pretty reliable to start 
 and will oscillate somewhere with most crystals from kHz to MHz.
 As you found out, it will often come up on one of many overtones.
 To reduce chance of coming at an overtone, a series resistor from logic 
 gate output to the crystal is often enough. If not, a RC low-pass will cut 
 down even further (although of course adding phase shift.)
>>>
>>> This is certainly the easiest and fastest way for a go/no-go test and to 
>>> find the approximate resonance frequency.
>>> In the attached circuit diagram make CX1 and CX2 about 10 pF and RGK 
>>> several MegOhms.
>>> The inverter gate should be preferably an unbuffered HCMOS or other fast 
>>> inverter.
>>> For crystals in the MHz range you can replace RV by a short, for kHz 
>>> crystals make it a few kOhms. If testing small watch crystals @ 32768 kHz 
>>> or around, RV should be 100 kOhm at least. RV reduces the crystal drive 
>>> level (RF current) to an acceptable level to avoid overloading or even 
>>> damaging of the crystal. For low frequency crystals the RV-CX2 lowpass also 
>>> avoids start-up at the overtone.
>>> It is recommended to add a second inverter gate at the output to isolate 
>>> your oscilloscope or counter input from the oscillator stage. Add some >330 
>>> ohm in series to the output of the 2nd inverter, if you connect a coaxial 
>>> cable. Then terminate the coax at the oscilloscope or frequency counter end 
>>> with 50 Ohms, so the square wave form will be roughly maintained.
>>>
>>> In this circuit the crystal will not operate at its series resonance, but 
>>> at a load resonance with load capacitance of something between 8 pF and 10 
>>> pF (depending on the inverter input and output capacitance plus the stray 
>>> capacitances of your test fixture).
>>> If you want to operate the oscillator at a (low) overtone, such as 3rd (or 
>>> maybe 5th), you must add a series combination of 10 nF plus an inductor in 
>>> parallel to CX2. The 10 nF is to avoid DC short-circuiting of the output. 
>>> The inductor together with CX2 must have a resonance frequency mid between 
>>> fundamental mode and 3rd overtone (not at one of them). So the tuned 
>>> circuit acts like a capacitor at the 3rd OT and is inductive at fundamental 
>>> mode (thus the phase condition for oscillation is not fulfilled at the 
>>> fundamental mode)
>>> Have fun
>>>
>>> Bernd
>>> DK1AG
>>> ___
>>> 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.
>>
>> "The power of accurate observation is commonly called cynicism by those who 
>> have not got it. »
>> George Bernard Shaw
>>
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
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>> and follow the instructions there.
>
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Re: [time-nuts] How to get unknown frequency quartz crystals oscillating

[Bob Camp]

Hi

There are two things you may be talking about:

1) The pressure springs on things like FT-243 holders, they are generic springs.

2) The connection leads on plated blanks, they are indeed strange *and* 
soldering to the blank is a big problem. 

I’m guessing you are in bucket number 2. 

Bob


> On Jun 4, 2016, at 1:41 PM, Mike Cook  wrote:
> 
> Thanks all for your advice, hints, tips and links. Lots to read , do and some 
> hardware to check.  I don’t have a frequency generator so I’ll have to go 
> another route. 
> 
> Oh. One last Q. Has anyone tried repairing the « spring » wire electric 
> connections on large quartz plates. In one large unit I have they had 
> corroded and dropped the plate, luckily no damage.  I have done one, but I 
> have no Idea what the original wire composition was so have certainly induced 
> some stray capacitance/resistance. It is possible that it was a filter rather 
> than a frequency source as it was not in a vacuum. 
> 
> Have a good one.
> 
>> Le 4 juin 2016 à 18:49, Bernd Neubig  a écrit :
>> 
>> 
>> Tim Shoppa wrote:
>>> The Pierce logic-gate-biased-active oscillator is pretty reliable to start 
>>> and will oscillate somewhere with most crystals from kHz to MHz.
>>> As you found out, it will often come up on one of many overtones.
>>> To reduce chance of coming at an overtone, a series resistor from logic 
>>> gate output to the crystal is often enough. If not, a RC low-pass will cut 
>>> down even further (although of course adding phase shift.)
>> 
>> This is certainly the easiest and fastest way for a go/no-go test and to 
>> find the approximate resonance frequency. 
>> In the attached circuit diagram make CX1 and CX2 about 10 pF and RGK several 
>> MegOhms.
>> The inverter gate should be preferably an unbuffered HCMOS or other fast 
>> inverter.
>> For crystals in the MHz range you can replace RV by a short, for kHz 
>> crystals make it a few kOhms. If testing small watch crystals @ 32768 kHz or 
>> around, RV should be 100 kOhm at least. RV reduces the crystal drive level 
>> (RF current) to an acceptable level to avoid overloading or even damaging of 
>> the crystal. For low frequency crystals the RV-CX2 lowpass also avoids 
>> start-up at the overtone.
>> It is recommended to add a second inverter gate at the output to isolate 
>> your oscilloscope or counter input from the oscillator stage. Add some >330 
>> ohm in series to the output of the 2nd inverter, if you connect a coaxial 
>> cable. Then terminate the coax at the oscilloscope or frequency counter end 
>> with 50 Ohms, so the square wave form will be roughly maintained.
>> 
>> In this circuit the crystal will not operate at its series resonance, but at 
>> a load resonance with load capacitance of something between 8 pF and 10 pF 
>> (depending on the inverter input and output capacitance plus the stray 
>> capacitances of your test fixture).
>> If you want to operate the oscillator at a (low) overtone, such as 3rd (or 
>> maybe 5th), you must add a series combination of 10 nF plus an inductor in 
>> parallel to CX2. The 10 nF is to avoid DC short-circuiting of the output. 
>> The inductor together with CX2 must have a resonance frequency mid between 
>> fundamental mode and 3rd overtone (not at one of them). So the tuned circuit 
>> acts like a capacitor at the 3rd OT and is inductive at fundamental mode 
>> (thus the phase condition for oscillation is not fulfilled at the 
>> fundamental mode)
>> Have fun
>> 
>> Bernd
>> DK1AG 
>> ___
>> 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.
> 
> "The power of accurate observation is commonly called cynicism by those who 
> have not got it. »
> George Bernard Shaw
> 
> ___
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> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Re: [time-nuts] How to get unknown frequency quartz crystals oscillating

[Brooke Clarke]

Hi George:

A Crystal Activity Meter is the most straight forward way:
http://www.prc68.com/I/Xam.html

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

 Original Message 

Hi,

I have a number of crystals either in glass, bakelite, ceramic or metal 
housings that I would like to get resonating . They are of three basic types.
  Square, or rectangular flat
  Round flat
  Bar  square section
Sizes range from 2-10cm or more in the longest face.

Some have frequency markings. ranging from IKHz 5MHz.
Others have none.
Some are of  Military origin, probably radios and as they have markings I can 
probably find a schematic from the radios to see how to proceed.  There may be 
dedicated testers still around. I am not so interested in this bunch at the 
moment.
Others have no known origin so I have no idea what oscillator circuits were 
used with them.
In terms of vintage, I would guess pre 1940  to late 50s

I have built a little Pierce circuit an tried a few. Some of the later 1-5MHz 
crystals will oscillate but there are a lot of parasitic signals as well as the 
supposed fundamental. I cannot make any of the low frequency / big crystals to 
react.

So my question:
If you had a crystal with unknown frequency and drive requirements that you 
wanted to investigate. How would you go about it?

If I can get them going I will share the Adevs. I don’t have a spectrum 
analyser so I can’t do phase noise.

Regards

"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] How to get unknown frequency quartz crystals oscillating

[Szeker K.]

Mike,

XTALs does work in air, or better: dry gases (i.e. nitrogen) too, but OK;
quality exemplares are (for better, spurious free, oscillating) in vacuum...

Karl


Virenfrei.
www.avast.com

<#DDB4FAA8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

2016-06-04 19:41 GMT+02:00 Mike Cook :

> Thanks all for your advice, hints, tips and links. Lots to read , do and
> some hardware to check.  I don’t have a frequency generator so I’ll have to
> go another route.
>
> Oh. One last Q. Has anyone tried repairing the « spring » wire electric
> connections on large quartz plates. In one large unit I have they had
> corroded and dropped the plate, luckily no damage.  I have done one, but I
> have no Idea what the original wire composition was so have certainly
> induced some stray capacitance/resistance. It is possible that it was a
> filter rather than a frequency source as it was not in a vacuum.
>
> Have a good one.
>
> > Le 4 juin 2016 à 18:49, Bernd Neubig  a écrit :
> >
> >
> > Tim Shoppa wrote:
> >> The Pierce logic-gate-biased-active oscillator is pretty reliable to
> start and will oscillate somewhere with most crystals from kHz to MHz.
> >> As you found out, it will often come up on one of many overtones.
> >> To reduce chance of coming at an overtone, a series resistor from logic
> gate output to the crystal is often enough. If not, a RC low-pass will cut
> down even further (although of course adding phase shift.)
> >
> > This is certainly the easiest and fastest way for a go/no-go test and to
> find the approximate resonance frequency.
> > In the attached circuit diagram make CX1 and CX2 about 10 pF and RGK
> several MegOhms.
> > The inverter gate should be preferably an unbuffered HCMOS or other fast
> inverter.
> > For crystals in the MHz range you can replace RV by a short, for kHz
> crystals make it a few kOhms. If testing small watch crystals @ 32768 kHz
> or around, RV should be 100 kOhm at least. RV reduces the crystal drive
> level (RF current) to an acceptable level to avoid overloading or even
> damaging of the crystal. For low frequency crystals the RV-CX2 lowpass also
> avoids start-up at the overtone.
> > It is recommended to add a second inverter gate at the output to isolate
> your oscilloscope or counter input from the oscillator stage. Add some >330
> ohm in series to the output of the 2nd inverter, if you connect a coaxial
> cable. Then terminate the coax at the oscilloscope or frequency counter end
> with 50 Ohms, so the square wave form will be roughly maintained.
> >
> > In this circuit the crystal will not operate at its series resonance,
> but at a load resonance with load capacitance of something between 8 pF and
> 10 pF (depending on the inverter input and output capacitance plus the
> stray capacitances of your test fixture).
> > If you want to operate the oscillator at a (low) overtone, such as 3rd
> (or maybe 5th), you must add a series combination of 10 nF plus an inductor
> in parallel to CX2. The 10 nF is to avoid DC short-circuiting of the
> output. The inductor together with CX2 must have a resonance frequency mid
> between fundamental mode and 3rd overtone (not at one of them). So the
> tuned circuit acts like a capacitor at the 3rd OT and is inductive at
> fundamental mode (thus the phase condition for oscillation is not fulfilled
> at the fundamental mode)
> > Have fun
> >
> > Bernd
> > DK1AG
> > ___
> > 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.
>
> "The power of accurate observation is commonly called cynicism by those
> who have not got it. »
> George Bernard Shaw
>
> ___
> 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] How to get unknown frequency quartz crystals oscillating

[Charles Steinmetz]

Tim wrote:


The Pierce logic-gate-biased-active oscillator is pretty reliable to start
and will oscillate somewhere with most crystals from kHz to MHz.

As you found out, it will often come up on one of many overtones.

To reduce chance of coming at an overtone, a series resistor from logic
gate output to the crystal is often enough. If not, a RC low-pass will cut
down even further (although of course adding phase shift.)


The general strategy for discouraging overtone operation and other 
unwanted modes at frequencies above the crystal fundamental is to design 
the gain element to have decreasing gain at higher frequencies.  The 
figure attached below (from Hayward's "introduction to RF Design") shows 
one common implementation.


One of Bernd's papers has some helpful information about low-frequency 
crystals and oscillator circuits.  See pp. 1-3 of:




Best regards,

Charles


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Re: [time-nuts] How to get unknown frequency quartz crystals oscillating

[Mike Cook]

Thanks all for your advice, hints, tips and links. Lots to read , do and some 
hardware to check.  I don’t have a frequency generator so I’ll have to go 
another route. 

Oh. One last Q. Has anyone tried repairing the « spring » wire electric 
connections on large quartz plates. In one large unit I have they had corroded 
and dropped the plate, luckily no damage.  I have done one, but I have no Idea 
what the original wire composition was so have certainly induced some stray 
capacitance/resistance. It is possible that it was a filter rather than a 
frequency source as it was not in a vacuum. 

Have a good one.

> Le 4 juin 2016 à 18:49, Bernd Neubig  a écrit :
> 
> 
> Tim Shoppa wrote:
>> The Pierce logic-gate-biased-active oscillator is pretty reliable to start 
>> and will oscillate somewhere with most crystals from kHz to MHz.
>> As you found out, it will often come up on one of many overtones.
>> To reduce chance of coming at an overtone, a series resistor from logic gate 
>> output to the crystal is often enough. If not, a RC low-pass will cut down 
>> even further (although of course adding phase shift.)
> 
> This is certainly the easiest and fastest way for a go/no-go test and to find 
> the approximate resonance frequency. 
> In the attached circuit diagram make CX1 and CX2 about 10 pF and RGK several 
> MegOhms.
> The inverter gate should be preferably an unbuffered HCMOS or other fast 
> inverter.
> For crystals in the MHz range you can replace RV by a short, for kHz crystals 
> make it a few kOhms. If testing small watch crystals @ 32768 kHz or around, 
> RV should be 100 kOhm at least. RV reduces the crystal drive level (RF 
> current) to an acceptable level to avoid overloading or even damaging of the 
> crystal. For low frequency crystals the RV-CX2 lowpass also avoids start-up 
> at the overtone.
> It is recommended to add a second inverter gate at the output to isolate your 
> oscilloscope or counter input from the oscillator stage. Add some >330 ohm in 
> series to the output of the 2nd inverter, if you connect a coaxial cable. 
> Then terminate the coax at the oscilloscope or frequency counter end with 50 
> Ohms, so the square wave form will be roughly maintained.
> 
> In this circuit the crystal will not operate at its series resonance, but at 
> a load resonance with load capacitance of something between 8 pF and 10 pF 
> (depending on the inverter input and output capacitance plus the stray 
> capacitances of your test fixture).
> If you want to operate the oscillator at a (low) overtone, such as 3rd (or 
> maybe 5th), you must add a series combination of 10 nF plus an inductor in 
> parallel to CX2. The 10 nF is to avoid DC short-circuiting of the output. The 
> inductor together with CX2 must have a resonance frequency mid between 
> fundamental mode and 3rd overtone (not at one of them). So the tuned circuit 
> acts like a capacitor at the 3rd OT and is inductive at fundamental mode 
> (thus the phase condition for oscillation is not fulfilled at the fundamental 
> mode)
> Have fun
> 
> Bernd
> DK1AG 
> ___
> 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.

"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] How to get unknown frequency quartz crystals oscillating

[Bernd Neubig]

Tim Shoppa wrote:
>The Pierce logic-gate-biased-active oscillator is pretty reliable to start and 
>will oscillate somewhere with most crystals from kHz to MHz.
>As you found out, it will often come up on one of many overtones.
>To reduce chance of coming at an overtone, a series resistor from logic gate 
>output to the crystal is often enough. If not, a RC low-pass will cut down 
>even further (although of course adding phase shift.)

This is certainly the easiest and fastest way for a go/no-go test and to find 
the approximate resonance frequency. 
In the attached circuit diagram make CX1 and CX2 about 10 pF and RGK several 
MegOhms.
The inverter gate should be preferably an unbuffered HCMOS or other fast 
inverter.
For crystals in the MHz range you can replace RV by a short, for kHz crystals 
make it a few kOhms. If testing small watch crystals @ 32768 kHz or around, RV 
should be 100 kOhm at least. RV reduces the crystal drive level (RF current) to 
an acceptable level to avoid overloading or even damaging of the crystal. For 
low frequency crystals the RV-CX2 lowpass also avoids start-up at the overtone.
It is recommended to add a second inverter gate at the output to isolate your 
oscilloscope or counter input from the oscillator stage. Add some >330 ohm in 
series to the output of the 2nd inverter, if you connect a coaxial cable. Then 
terminate the coax at the oscilloscope or frequency counter end with 50 Ohms, 
so the square wave form will be roughly maintained.

In this circuit the crystal will not operate at its series resonance, but at a 
load resonance with load capacitance of something between 8 pF and 10 pF 
(depending on the inverter input and output capacitance plus the stray 
capacitances of your test fixture).
If you want to operate the oscillator at a (low) overtone, such as 3rd (or 
maybe 5th), you must add a series combination of 10 nF plus an inductor in 
parallel to CX2. The 10 nF is to avoid DC short-circuiting of the output. The 
inductor together with CX2 must have a resonance frequency mid between 
fundamental mode and 3rd overtone (not at one of them). So the tuned circuit 
acts like a capacitor at the 3rd OT and is inductive at fundamental mode (thus 
the phase condition for oscillation is not fulfilled at the fundamental mode)
Have fun

Bernd
DK1AG 
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Re: [time-nuts] How to get unknown frequency quartz crystals oscillating

[Tim Shoppa]

With random old crystals in holders, it often helps to disassemble the
holder and clean crystal and holder plates with alcohol (my favorite back
in my youth was carbon tetracholoride but not so easy to find these days.)
I'm guessing most of your round blanks were for FT-243 type holders.

The Pierce logic-gate-biased-active oscillator is pretty reliable to start
and will oscillate somewhere with most crystals from kHz to MHz.

As you found out, it will often come up on one of many overtones.

To reduce chance of coming at an overtone, a series resistor from logic
gate output to the crystal is often enough. If not, a RC low-pass will cut
down even further (although of course adding phase shift.)

Many surplus crystals from the 50's will be marked with their series
resonant frequency. The military surplus tank crystals are marked with
channel number. By the 60's and 70's, crystals for VHF radios were often
marked with the channel frequency (that's after multiplication and mixing
with IF if a receive crystal.)

Tim N3QE

On Sat, Jun 4, 2016 at 4:46 AM, Mike Cook  wrote:

> Hi,
>
> I have a number of crystals either in glass, bakelite, ceramic or metal
> housings that I would like to get resonating . They are of three basic
> types.
>  Square, or rectangular flat
>  Round flat
>  Bar  square section
> Sizes range from 2-10cm or more in the longest face.
>
> Some have frequency markings. ranging from IKHz 5MHz.
> Others have none.
> Some are of  Military origin, probably radios and as they have markings I
> can probably find a schematic from the radios to see how to proceed.  There
> may be dedicated testers still around. I am not so interested in this bunch
> at the moment.
> Others have no known origin so I have no idea what oscillator circuits
> were used with them.
> In terms of vintage, I would guess pre 1940  to late 50s
>
> I have built a little Pierce circuit an tried a few. Some of the later
> 1-5MHz crystals will oscillate but there are a lot of parasitic signals as
> well as the supposed fundamental. I cannot make any of the low frequency /
> big crystals to react.
>
> So my question:
> If you had a crystal with unknown frequency and drive requirements that
> you wanted to investigate. How would you go about it?
>
> If I can get them going I will share the Adevs. I don’t have a spectrum
> analyser so I can’t do phase noise.
>
> Regards
>
> "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] How to get unknown frequency quartz crystals oscillating

[Bob Camp]

Hi

Simple approach is to assume that you have a crystal resistance in the range of 
100K ohms. If you guess to 
high, the oscillator will just work to well :)

Multiple JFETS in cascade for the higher frequency stuff should work. For 
anything below 20 KHz, an op-amp
is likely your best bet.

A spectrum analyzer with a tracking generator will give you some idea of their 
impedance and *if* they still have 
any activity at all. 

Bob

> On Jun 4, 2016, at 4:46 AM, Mike Cook  wrote:
> 
> Hi,
> 
> I have a number of crystals either in glass, bakelite, ceramic or metal 
> housings that I would like to get resonating . They are of three basic types.
> Square, or rectangular flat   
> Round flat 
> Bar  square section
> Sizes range from 2-10cm or more in the longest face.
> 
> Some have frequency markings. ranging from IKHz 5MHz. 
> Others have none.
> Some are of  Military origin, probably radios and as they have markings I can 
> probably find a schematic from the radios to see how to proceed.  There may 
> be dedicated testers still around. I am not so interested in this bunch at 
> the moment. 
> Others have no known origin so I have no idea what oscillator circuits were 
> used with them. 
> In terms of vintage, I would guess pre 1940  to late 50s 
> 
> I have built a little Pierce circuit an tried a few. Some of the later 1-5MHz 
> crystals will oscillate but there are a lot of parasitic signals as well as 
> the supposed fundamental. I cannot make any of the low frequency / big 
> crystals to react.
> 
> So my question:
> If you had a crystal with unknown frequency and drive requirements that you 
> wanted to investigate. How would you go about it?
> 
> If I can get them going I will share the Adevs. I don’t have a spectrum 
> analyser so I can’t do phase noise.
> 
> Regards
> 
> "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] How to get unknown frequency quartz crystals oscillating

[Bruce Griffiths]

A vector voltmeter can be replaced by a spectrum analyser or even a 14 bit 
scope with or without a preamp. In lieu of phase information one can measure 
the 3dB bandwidth to elicit the Q, combined with measurement of the low 
frequency shunt capacitance and the attenuation at resonance, the crystal 
parameters can be extracted without knowledge of the phase shift.
Bruce
  

On Saturday, 4 June 2016 11:01 PM, Bruce Griffiths 
 wrote:
 

 On reflection, building a jig to measure the crystal transmission as a 
function of frequency may be much easier than attempting to build an oscillator 
for an unknown crystal. However a suitable signal generator and detector are 
required.
Once the crystal parameters are known its much easier to design a suitable 
oscillator circuit. Measuring the location of spurious resonances may also be 
useful.

Bruce
 

    On Saturday, 4 June 2016 9:52 PM, Bruce Griffiths 
 wrote:
 

 Some idea of the crystal equivalent circuit at the oscillation frequency would 
help considerably. Usually lower frequency crystals have a considerably higher 
series resistance than those operated at 1MHz or above.
At frequencies below 100kHz or so a Meacham bridge using something likke a 
wideband FET opamp may be feasible.
Bruce
 

    On Saturday, 4 June 2016 9:01 PM, Mike Cook  wrote:
 

 Hi,

I have a number of crystals either in glass, bakelite, ceramic or metal 
housings that I would like to get resonating . They are of three basic types.
 Square, or rectangular flat  
 Round flat 
 Bar  square section
Sizes range from 2-10cm or more in the longest face.

Some have frequency markings. ranging from IKHz 5MHz. 
Others have none.
Some are of  Military origin, probably radios and as they have markings I can 
probably find a schematic from the radios to see how to proceed.  There may be 
dedicated testers still around. I am not so interested in this bunch at the 
moment. 
Others have no known origin so I have no idea what oscillator circuits were 
used with them. 
In terms of vintage, I would guess pre 1940  to late 50s 

I have built a little Pierce circuit an tried a few. Some of the later 1-5MHz 
crystals will oscillate but there are a lot of parasitic signals as well as the 
supposed fundamental. I cannot make any of the low frequency / big crystals to 
react.

So my question:
If you had a crystal with unknown frequency and drive requirements that you 
wanted to investigate. How would you go about it?

If I can get them going I will share the Adevs. I don’t have a spectrum 
analyser so I can’t do phase noise.

Regards

"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] How to get unknown frequency quartz crystals oscillating

[Bruce Griffiths]

Some idea of the crystal equivalent circuit at the oscillation frequency would 
help considerably. Usually lower frequency crystals have a considerably higher 
series resistance than those operated at 1MHz or above.
At frequencies below 100kHz or so a Meacham bridge using something likke a 
wideband FET opamp may be feasible.
Bruce
 

On Saturday, 4 June 2016 9:01 PM, Mike Cook  wrote:
 

 Hi,

I have a number of crystals either in glass, bakelite, ceramic or metal 
housings that I would like to get resonating . They are of three basic types.
 Square, or rectangular flat  
 Round flat 
 Bar  square section
Sizes range from 2-10cm or more in the longest face.

Some have frequency markings. ranging from IKHz 5MHz. 
Others have none.
Some are of  Military origin, probably radios and as they have markings I can 
probably find a schematic from the radios to see how to proceed.  There may be 
dedicated testers still around. I am not so interested in this bunch at the 
moment. 
Others have no known origin so I have no idea what oscillator circuits were 
used with them. 
In terms of vintage, I would guess pre 1940  to late 50s 

I have built a little Pierce circuit an tried a few. Some of the later 1-5MHz 
crystals will oscillate but there are a lot of parasitic signals as well as the 
supposed fundamental. I cannot make any of the low frequency / big crystals to 
react.

So my question:
If you had a crystal with unknown frequency and drive requirements that you 
wanted to investigate. How would you go about it?

If I can get them going I will share the Adevs. I don’t have a spectrum 
analyser so I can’t do phase noise.

Regards

"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] How to get unknown frequency quartz crystals oscillating

[Bruce Griffiths]

On reflection, building a jig to measure the crystal transmission as a function 
of frequency may be much easier than attempting to build an oscillator for an 
unknown crystal. However a suitable signal generator and detector are required.
Once the crystal parameters are known its much easier to design a suitable 
oscillator circuit. Measuring the location of spurious resonances may also be 
useful.

Bruce
 

On Saturday, 4 June 2016 9:52 PM, Bruce Griffiths 
 wrote:
 

 Some idea of the crystal equivalent circuit at the oscillation frequency would 
help considerably. Usually lower frequency crystals have a considerably higher 
series resistance than those operated at 1MHz or above.
At frequencies below 100kHz or so a Meacham bridge using something likke a 
wideband FET opamp may be feasible.
Bruce
 

On Saturday, 4 June 2016 9:01 PM, Mike Cook  wrote:
 

 Hi,

I have a number of crystals either in glass, bakelite, ceramic or metal 
housings that I would like to get resonating . They are of three basic types.
 Square, or rectangular flat  
 Round flat 
 Bar  square section
Sizes range from 2-10cm or more in the longest face.

Some have frequency markings. ranging from IKHz 5MHz. 
Others have none.
Some are of  Military origin, probably radios and as they have markings I can 
probably find a schematic from the radios to see how to proceed.  There may be 
dedicated testers still around. I am not so interested in this bunch at the 
moment. 
Others have no known origin so I have no idea what oscillator circuits were 
used with them. 
In terms of vintage, I would guess pre 1940  to late 50s 

I have built a little Pierce circuit an tried a few. Some of the later 1-5MHz 
crystals will oscillate but there are a lot of parasitic signals as well as the 
supposed fundamental. I cannot make any of the low frequency / big crystals to 
react.

So my question:
If you had a crystal with unknown frequency and drive requirements that you 
wanted to investigate. How would you go about it?

If I can get them going I will share the Adevs. I don’t have a spectrum 
analyser so I can’t do phase noise.

Regards

"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] How to get unknown frequency quartz crystals oscillating

[Attila Kinali]

On Sat, 4 Jun 2016 10:46:40 +0200
Mike Cook  wrote:

> If you had a crystal with unknown frequency and drive requirements
> that you wanted to investigate. How would you go about it?

I would use some signal generator to generate a tunable sinusoid and
feed this to the quartz with the testing circuit from the standard
setup (see eg [1]) and measure the power on both sides of the quartz,
like in an VNA setup. You will probably not need the phase information,
so a simple power detector would be enough.

Bernd should be able to tell you way more about this than I can.

Attila Kinali

[1] "Load resonant measurements of quartz crystals", Dwane Rose, 1998
http://www.saunders-assoc.com/httpdocs/datasheets/paper/paper.pdf

-- 
Reading can seriously damage your ignorance.
-- unknown
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