View Full Version : Crystal Q measurement

Virgil Smith

December 29th 03, 04:35 AM

I have a bunch of oddball crystals that I want to test. I know I can just

build up a generic oscillator to find the

resonant frequency, but out of curiousity I would like to

know the quality of the things, too.

Anyone know of any neat ideas for measuring the Q of a

crystal?

I would welcome any and all suggestions,

-vs-

Tom Bruhns

December 29th 03, 08:08 AM

If you have access to old QSTs, you should be able to find articles

about measuring crystal parameters. Look especially for things by Wes

Hayward, W7ZOI. There's a fairly simple crystal-tester you can build

to measure enough parameters to extract equivalent L, Cs, Cp and R, I

believe. I 'spose someone will pop in with a more specific reference

for you.

Cheers,

Tom

"Virgil Smith" > wrote in message news:<3iNHb.504277$275.1417484@attbi_s53>...

> I have a bunch of oddball crystals that I want to test. I know I can just

> build up a generic oscillator to find the

> resonant frequency, but out of curiousity I would like to

> know the quality of the things, too.

>

> Anyone know of any neat ideas for measuring the Q of a

> crystal?

>

> I would welcome any and all suggestions,

>

> -vs-

Tom Bruhns

December 29th 03, 08:08 AM

If you have access to old QSTs, you should be able to find articles

about measuring crystal parameters. Look especially for things by Wes

Hayward, W7ZOI. There's a fairly simple crystal-tester you can build

to measure enough parameters to extract equivalent L, Cs, Cp and R, I

believe. I 'spose someone will pop in with a more specific reference

for you.

Cheers,

Tom

"Virgil Smith" > wrote in message news:<3iNHb.504277$275.1417484@attbi_s53>...

> I have a bunch of oddball crystals that I want to test. I know I can just

> build up a generic oscillator to find the

> resonant frequency, but out of curiousity I would like to

> know the quality of the things, too.

>

> Anyone know of any neat ideas for measuring the Q of a

> crystal?

>

> I would welcome any and all suggestions,

>

> -vs-

Joe McElvenney

December 29th 03, 08:49 AM

Hi,

To calculate Q at series resonance, you will need to

ascertain both the effective series resistance and one of

the series reactances (XL or XC). In his Jan/Feb 2002

article "Quartz Crystal Parameter Measurement", Jack

Hardcastle, G3JIR uses a simple test rig and a

mathematical/graphical method to determine both the

resistance and effective series capacitance.

There is an obvious error in the circuit to look out for

though, where an extra series crystal (Y2) was

inadvertently added by the draughtsman.

Cheers - Joe

Joe McElvenney

December 29th 03, 08:49 AM

Hi,

To calculate Q at series resonance, you will need to

ascertain both the effective series resistance and one of

the series reactances (XL or XC). In his Jan/Feb 2002

article "Quartz Crystal Parameter Measurement", Jack

Hardcastle, G3JIR uses a simple test rig and a

mathematical/graphical method to determine both the

resistance and effective series capacitance.

There is an obvious error in the circuit to look out for

though, where an extra series crystal (Y2) was

inadvertently added by the draughtsman.

Cheers - Joe

Joe McElvenney

December 29th 03, 08:53 AM

Oops!

I should have said that the article was in 'QEX'.

Cheers - Joe

Joe McElvenney

December 29th 03, 08:53 AM

Oops!

I should have said that the article was in 'QEX'.

Cheers - Joe

Virgil Smith

December 29th 03, 07:53 PM

"Joe McElvenney" > wrote in message

...

> Oops!

>

> I should have said that the article was in 'QEX'.

>

>

> Cheers - Joe

>

>

Hi, Joe:

Sounds like just what I need. Thanks a lot!

(Now to dig up the back issue of QEX.)

73,

-vs-

Virgil Smith

December 29th 03, 07:53 PM

"Joe McElvenney" > wrote in message

...

> Oops!

>

> I should have said that the article was in 'QEX'.

>

>

> Cheers - Joe

>

>

Hi, Joe:

Sounds like just what I need. Thanks a lot!

(Now to dig up the back issue of QEX.)

73,

-vs-

Nick Kennedy

December 30th 03, 07:23 PM

"Virgil Smith" > wrote in message news:<3iNHb.504277

>

> Anyone know of any neat ideas for measuring the Q of a

> crystal?

>

> I would welcome any and all suggestions,

>

> -vs-

Let's see if I can describe a method based on W7ZOI's efforts, with

some updates by K8IQY. By the way, the W7ZOI techniques from QST were

added as appendixes into one of Doug Demaw's ARRL books. Demaw

integrated Hayward's various test jigs into one crystal tester. You

can get a board from Far Circuits.

You put the crystal in a specific (typically 50 ohm) environment by

putting 50 ohm attenuators between generator and crystal and between

crystal and detector. The detector might be a diode detector plus

voltmeter or an oscilloscope. You'll also have another 50 ohm 3 dB

pad in series that can be switched in and out.

1. With the pad switched IN, adjust frequency until the peak output

is read (resonance). Note the center frequency and meter indication.

2. Switch the pad OUT and find the frequencies above and below the

center frequency that give the same indication. These are the + and –

3 dB frequencies and the difference between them is the bandwidth.

Now you can calculate Q by dividing the center frequency by the

bandwidth. Pretty low isn't it? This is a loaded Q, not the

crystal's Q. The total resistance in the circuit is 50 ohms source

plus 50 ohms load plus the crystal's yet unknown Rs.

3. Tune back to the center frequency where the output is at its peak.

Unplug the crystal and substitute a pot of maybe 0 to 25 ohms range.

(I actually just substitute fixed resistors since I don't have a

decent pot like this.) When you find a value that gives the same

meter indication as the crystal did, that is the value of Rs. (This

is because we are at series resonance, so Xc and XL have cancelled.)

Alright. Another formula for loaded Q is XL / R. R in this case is

100 ohms plus the Rs you just measured. And XL is 2*PI*Fc*L, where Fc

is the center frequency you measured earlier. You already have the

loaded Q from step 2, so you are down to one unknown. Just solve for

XL and/or L, which is the equivalent inductance of the crystal. In

like manner, you can find the series C, since Xc = XL.

And finally, the Q you wanted (the crystal's Q) is XL / Rs.

Now you know about everything about the crystal and can get one of

your Hayward or Demaw books and start designing some filters. Hayward

has nice software for this in both Introduction to RF Design and

Experimental Methods in RF Design, both from ARRL. If you want to

include holder (parallel) C in your modeling, 5 pF is a good estimate.

Jim Kortge, K8IQY puts his crystal in a 12.5 ohm environment by using

4:1 (impedance) bifilar transformers into and out of the crystals (50

ohm attenuators are still used though, to assure known generator and

load resistances). This has the advantage of making the resistance

measurement easier, but it makes the loaded bandwidth smaller, so you

need a good stable generator that you can read to the Hz. Those

little DDS units are nice. Be sure to use filtering if necessary for

signal purity. Jim designed a nice little VXO (variable crystal

oscillator) that uses one of the crystals from the set you are

measuring in the oscillator circuit. See it on NJQRP's page:

http://www.njqrp.org/pvxo/index.html

I followed Jim's lead but used resistive 50 to 12.5 ohm matching pads

instead of transformers. That way I got rid of any reactive effects

(which are minimal) of the transformers, but required a lot more

driving power due to the loss in the matching pads.

OK, that was probably more than you wanted to know. Hope I remembered

this stuff right.

73—Nick, WA5BDU

in Arkansas

Nick Kennedy

December 30th 03, 07:23 PM

"Virgil Smith" > wrote in message news:<3iNHb.504277

>

> Anyone know of any neat ideas for measuring the Q of a

> crystal?

>

> I would welcome any and all suggestions,

>

> -vs-

Let's see if I can describe a method based on W7ZOI's efforts, with

some updates by K8IQY. By the way, the W7ZOI techniques from QST were

added as appendixes into one of Doug Demaw's ARRL books. Demaw

integrated Hayward's various test jigs into one crystal tester. You

can get a board from Far Circuits.

You put the crystal in a specific (typically 50 ohm) environment by

putting 50 ohm attenuators between generator and crystal and between

crystal and detector. The detector might be a diode detector plus

voltmeter or an oscilloscope. You'll also have another 50 ohm 3 dB

pad in series that can be switched in and out.

1. With the pad switched IN, adjust frequency until the peak output

is read (resonance). Note the center frequency and meter indication.

2. Switch the pad OUT and find the frequencies above and below the

center frequency that give the same indication. These are the + and –

3 dB frequencies and the difference between them is the bandwidth.

Now you can calculate Q by dividing the center frequency by the

bandwidth. Pretty low isn't it? This is a loaded Q, not the

crystal's Q. The total resistance in the circuit is 50 ohms source

plus 50 ohms load plus the crystal's yet unknown Rs.

3. Tune back to the center frequency where the output is at its peak.

Unplug the crystal and substitute a pot of maybe 0 to 25 ohms range.

(I actually just substitute fixed resistors since I don't have a

decent pot like this.) When you find a value that gives the same

meter indication as the crystal did, that is the value of Rs. (This

is because we are at series resonance, so Xc and XL have cancelled.)

Alright. Another formula for loaded Q is XL / R. R in this case is

100 ohms plus the Rs you just measured. And XL is 2*PI*Fc*L, where Fc

is the center frequency you measured earlier. You already have the

loaded Q from step 2, so you are down to one unknown. Just solve for

XL and/or L, which is the equivalent inductance of the crystal. In

like manner, you can find the series C, since Xc = XL.

And finally, the Q you wanted (the crystal's Q) is XL / Rs.

Now you know about everything about the crystal and can get one of

your Hayward or Demaw books and start designing some filters. Hayward

has nice software for this in both Introduction to RF Design and

Experimental Methods in RF Design, both from ARRL. If you want to

include holder (parallel) C in your modeling, 5 pF is a good estimate.

Jim Kortge, K8IQY puts his crystal in a 12.5 ohm environment by using

4:1 (impedance) bifilar transformers into and out of the crystals (50

ohm attenuators are still used though, to assure known generator and

load resistances). This has the advantage of making the resistance

measurement easier, but it makes the loaded bandwidth smaller, so you

need a good stable generator that you can read to the Hz. Those

little DDS units are nice. Be sure to use filtering if necessary for

signal purity. Jim designed a nice little VXO (variable crystal

oscillator) that uses one of the crystals from the set you are

measuring in the oscillator circuit. See it on NJQRP's page:

http://www.njqrp.org/pvxo/index.html

I followed Jim's lead but used resistive 50 to 12.5 ohm matching pads

instead of transformers. That way I got rid of any reactive effects

(which are minimal) of the transformers, but required a lot more

driving power due to the loss in the matching pads.

OK, that was probably more than you wanted to know. Hope I remembered

this stuff right.

73—Nick, WA5BDU

in Arkansas

W3JDR

December 30th 03, 11:20 PM

See the "Examples" section of my web site to see how a DDS signal generator

and a little software makes these measurements easy:

http://mysite.verizon.net/jdrocci/

Joe

W3JDR

"Nick Kennedy" > wrote in message

om...

> "Virgil Smith" > wrote in message news:<3iNHb.504277

> >

> > Anyone know of any neat ideas for measuring the Q of a

> > crystal?

> >

> > I would welcome any and all suggestions,

> >

> > -vs-

>

> Let's see if I can describe a method based on W7ZOI's efforts, with

> some updates by K8IQY. By the way, the W7ZOI techniques from QST were

> added as appendixes into one of Doug Demaw's ARRL books. Demaw

> integrated Hayward's various test jigs into one crystal tester. You

> can get a board from Far Circuits.

>

> You put the crystal in a specific (typically 50 ohm) environment by

> putting 50 ohm attenuators between generator and crystal and between

> crystal and detector. The detector might be a diode detector plus

> voltmeter or an oscilloscope. You'll also have another 50 ohm 3 dB

> pad in series that can be switched in and out.

>

> 1. With the pad switched IN, adjust frequency until the peak output

> is read (resonance). Note the center frequency and meter indication.

>

> 2. Switch the pad OUT and find the frequencies above and below the

> center frequency that give the same indication. These are the + and -

> 3 dB frequencies and the difference between them is the bandwidth.

>

> Now you can calculate Q by dividing the center frequency by the

> bandwidth. Pretty low isn't it? This is a loaded Q, not the

> crystal's Q. The total resistance in the circuit is 50 ohms source

> plus 50 ohms load plus the crystal's yet unknown Rs.

>

> 3. Tune back to the center frequency where the output is at its peak.

> Unplug the crystal and substitute a pot of maybe 0 to 25 ohms range.

> (I actually just substitute fixed resistors since I don't have a

> decent pot like this.) When you find a value that gives the same

> meter indication as the crystal did, that is the value of Rs. (This

> is because we are at series resonance, so Xc and XL have cancelled.)

>

> Alright. Another formula for loaded Q is XL / R. R in this case is

> 100 ohms plus the Rs you just measured. And XL is 2*PI*Fc*L, where Fc

> is the center frequency you measured earlier. You already have the

> loaded Q from step 2, so you are down to one unknown. Just solve for

> XL and/or L, which is the equivalent inductance of the crystal. In

> like manner, you can find the series C, since Xc = XL.

>

> And finally, the Q you wanted (the crystal's Q) is XL / Rs.

>

> Now you know about everything about the crystal and can get one of

> your Hayward or Demaw books and start designing some filters. Hayward

> has nice software for this in both Introduction to RF Design and

> Experimental Methods in RF Design, both from ARRL. If you want to

> include holder (parallel) C in your modeling, 5 pF is a good estimate.

>

> Jim Kortge, K8IQY puts his crystal in a 12.5 ohm environment by using

> 4:1 (impedance) bifilar transformers into and out of the crystals (50

> ohm attenuators are still used though, to assure known generator and

> load resistances). This has the advantage of making the resistance

> measurement easier, but it makes the loaded bandwidth smaller, so you

> need a good stable generator that you can read to the Hz. Those

> little DDS units are nice. Be sure to use filtering if necessary for

> signal purity. Jim designed a nice little VXO (variable crystal

> oscillator) that uses one of the crystals from the set you are

> measuring in the oscillator circuit. See it on NJQRP's page:

>

> http://www.njqrp.org/pvxo/index.html

>

> I followed Jim's lead but used resistive 50 to 12.5 ohm matching pads

> instead of transformers. That way I got rid of any reactive effects

> (which are minimal) of the transformers, but required a lot more

> driving power due to the loss in the matching pads.

>

> OK, that was probably more than you wanted to know. Hope I remembered

> this stuff right.

>

> 73-Nick, WA5BDU

> in Arkansas

W3JDR

December 30th 03, 11:20 PM

See the "Examples" section of my web site to see how a DDS signal generator

and a little software makes these measurements easy:

http://mysite.verizon.net/jdrocci/

Joe

W3JDR

"Nick Kennedy" > wrote in message

om...

> "Virgil Smith" > wrote in message news:<3iNHb.504277

> >

> > Anyone know of any neat ideas for measuring the Q of a

> > crystal?

> >

> > I would welcome any and all suggestions,

> >

> > -vs-

>

> Let's see if I can describe a method based on W7ZOI's efforts, with

> some updates by K8IQY. By the way, the W7ZOI techniques from QST were

> added as appendixes into one of Doug Demaw's ARRL books. Demaw

> integrated Hayward's various test jigs into one crystal tester. You

> can get a board from Far Circuits.

>

> You put the crystal in a specific (typically 50 ohm) environment by

> putting 50 ohm attenuators between generator and crystal and between

> crystal and detector. The detector might be a diode detector plus

> voltmeter or an oscilloscope. You'll also have another 50 ohm 3 dB

> pad in series that can be switched in and out.

>

> 1. With the pad switched IN, adjust frequency until the peak output

> is read (resonance). Note the center frequency and meter indication.

>

> 2. Switch the pad OUT and find the frequencies above and below the

> center frequency that give the same indication. These are the + and -

> 3 dB frequencies and the difference between them is the bandwidth.

>

> Now you can calculate Q by dividing the center frequency by the

> bandwidth. Pretty low isn't it? This is a loaded Q, not the

> crystal's Q. The total resistance in the circuit is 50 ohms source

> plus 50 ohms load plus the crystal's yet unknown Rs.

>

> 3. Tune back to the center frequency where the output is at its peak.

> Unplug the crystal and substitute a pot of maybe 0 to 25 ohms range.

> (I actually just substitute fixed resistors since I don't have a

> decent pot like this.) When you find a value that gives the same

> meter indication as the crystal did, that is the value of Rs. (This

> is because we are at series resonance, so Xc and XL have cancelled.)

>

> Alright. Another formula for loaded Q is XL / R. R in this case is

> 100 ohms plus the Rs you just measured. And XL is 2*PI*Fc*L, where Fc

> is the center frequency you measured earlier. You already have the

> loaded Q from step 2, so you are down to one unknown. Just solve for

> XL and/or L, which is the equivalent inductance of the crystal. In

> like manner, you can find the series C, since Xc = XL.

>

> And finally, the Q you wanted (the crystal's Q) is XL / Rs.

>

> Now you know about everything about the crystal and can get one of

> your Hayward or Demaw books and start designing some filters. Hayward

> has nice software for this in both Introduction to RF Design and

> Experimental Methods in RF Design, both from ARRL. If you want to

> include holder (parallel) C in your modeling, 5 pF is a good estimate.

>

> Jim Kortge, K8IQY puts his crystal in a 12.5 ohm environment by using

> 4:1 (impedance) bifilar transformers into and out of the crystals (50

> ohm attenuators are still used though, to assure known generator and

> load resistances). This has the advantage of making the resistance

> measurement easier, but it makes the loaded bandwidth smaller, so you

> need a good stable generator that you can read to the Hz. Those

> little DDS units are nice. Be sure to use filtering if necessary for

> signal purity. Jim designed a nice little VXO (variable crystal

> oscillator) that uses one of the crystals from the set you are

> measuring in the oscillator circuit. See it on NJQRP's page:

>

> http://www.njqrp.org/pvxo/index.html

>

> I followed Jim's lead but used resistive 50 to 12.5 ohm matching pads

> instead of transformers. That way I got rid of any reactive effects

> (which are minimal) of the transformers, but required a lot more

> driving power due to the loss in the matching pads.

>

> OK, that was probably more than you wanted to know. Hope I remembered

> this stuff right.

>

> 73-Nick, WA5BDU

> in Arkansas

Virgil Smith

December 31st 03, 08:48 PM

"Nick Kennedy" > wrote in message

om...

> "Virgil Smith" > wrote in message news:<3iNHb.504277

> >

> > Anyone know of any neat ideas for measuring the Q of a

> > crystal?

> >

> > I would welcome any and all suggestions,

> >

> > -vs-

>

> Let's see if I can describe a method based on W7ZOI's efforts, with

> some updates by K8IQY. By the way, the W7ZOI techniques from QST were

> added as appendixes into one of Doug Demaw's ARRL books. Demaw

> integrated Hayward's various test jigs into one crystal tester. You

> can get a board from Far Circuits.

>

> You put the crystal in a specific (typically 50 ohm) environment by

> putting 50 ohm attenuators between generator and crystal and between

> crystal and detector. The detector might be a diode detector plus

> voltmeter or an oscilloscope. You'll also have another 50 ohm 3 dB

> pad in series that can be switched in and out.

>

> 1. With the pad switched IN, adjust frequency until the peak output

> is read (resonance). Note the center frequency and meter indication.

>

> 2. Switch the pad OUT and find the frequencies above and below the

> center frequency that give the same indication. These are the + and -

> 3 dB frequencies and the difference between them is the bandwidth.

>

> Now you can calculate Q by dividing the center frequency by the

> bandwidth. Pretty low isn't it? This is a loaded Q, not the

> crystal's Q. The total resistance in the circuit is 50 ohms source

> plus 50 ohms load plus the crystal's yet unknown Rs.

>

> 3. Tune back to the center frequency where the output is at its peak.

> Unplug the crystal and substitute a pot of maybe 0 to 25 ohms range.

> (I actually just substitute fixed resistors since I don't have a

> decent pot like this.) When you find a value that gives the same

> meter indication as the crystal did, that is the value of Rs. (This

> is because we are at series resonance, so Xc and XL have cancelled.)

>

> Alright. Another formula for loaded Q is XL / R. R in this case is

> 100 ohms plus the Rs you just measured. And XL is 2*PI*Fc*L, where Fc

> is the center frequency you measured earlier. You already have the

> loaded Q from step 2, so you are down to one unknown. Just solve for

> XL and/or L, which is the equivalent inductance of the crystal. In

> like manner, you can find the series C, since Xc = XL.

>

> And finally, the Q you wanted (the crystal's Q) is XL / Rs.

>

> Now you know about everything about the crystal and can get one of

> your Hayward or Demaw books and start designing some filters. Hayward

> has nice software for this in both Introduction to RF Design and

> Experimental Methods in RF Design, both from ARRL. If you want to

> include holder (parallel) C in your modeling, 5 pF is a good estimate.

>

> Jim Kortge, K8IQY puts his crystal in a 12.5 ohm environment by using

> 4:1 (impedance) bifilar transformers into and out of the crystals (50

> ohm attenuators are still used though, to assure known generator and

> load resistances). This has the advantage of making the resistance

> measurement easier, but it makes the loaded bandwidth smaller, so you

> need a good stable generator that you can read to the Hz. Those

> little DDS units are nice. Be sure to use filtering if necessary for

> signal purity. Jim designed a nice little VXO (variable crystal

> oscillator) that uses one of the crystals from the set you are

> measuring in the oscillator circuit. See it on NJQRP's page:

>

> http://www.njqrp.org/pvxo/index.html

>

> I followed Jim's lead but used resistive 50 to 12.5 ohm matching pads

> instead of transformers. That way I got rid of any reactive effects

> (which are minimal) of the transformers, but required a lot more

> driving power due to the loss in the matching pads.

>

> OK, that was probably more than you wanted to know. Hope I remembered

> this stuff right.

>

> 73-Nick, WA5BDU

> in Arkansas

Hi, Nick,

No, not more than I wanted to know at all. I'm quite happy to have this

level

of info.

Thanks for the detailed reply -- gives me something to mull over during the

holidays.

-vs-

Virgil Smith

December 31st 03, 08:48 PM

"Nick Kennedy" > wrote in message

om...

> "Virgil Smith" > wrote in message news:<3iNHb.504277

> >

> > Anyone know of any neat ideas for measuring the Q of a

> > crystal?

> >

> > I would welcome any and all suggestions,

> >

> > -vs-

>

> Let's see if I can describe a method based on W7ZOI's efforts, with

> some updates by K8IQY. By the way, the W7ZOI techniques from QST were

> added as appendixes into one of Doug Demaw's ARRL books. Demaw

> integrated Hayward's various test jigs into one crystal tester. You

> can get a board from Far Circuits.

>

> You put the crystal in a specific (typically 50 ohm) environment by

> putting 50 ohm attenuators between generator and crystal and between

> crystal and detector. The detector might be a diode detector plus

> voltmeter or an oscilloscope. You'll also have another 50 ohm 3 dB

> pad in series that can be switched in and out.

>

> 1. With the pad switched IN, adjust frequency until the peak output

> is read (resonance). Note the center frequency and meter indication.

>

> 2. Switch the pad OUT and find the frequencies above and below the

> center frequency that give the same indication. These are the + and -

> 3 dB frequencies and the difference between them is the bandwidth.

>

> Now you can calculate Q by dividing the center frequency by the

> bandwidth. Pretty low isn't it? This is a loaded Q, not the

> crystal's Q. The total resistance in the circuit is 50 ohms source

> plus 50 ohms load plus the crystal's yet unknown Rs.

>

> 3. Tune back to the center frequency where the output is at its peak.

> Unplug the crystal and substitute a pot of maybe 0 to 25 ohms range.

> (I actually just substitute fixed resistors since I don't have a

> decent pot like this.) When you find a value that gives the same

> meter indication as the crystal did, that is the value of Rs. (This

> is because we are at series resonance, so Xc and XL have cancelled.)

>

> Alright. Another formula for loaded Q is XL / R. R in this case is

> 100 ohms plus the Rs you just measured. And XL is 2*PI*Fc*L, where Fc

> is the center frequency you measured earlier. You already have the

> loaded Q from step 2, so you are down to one unknown. Just solve for

> XL and/or L, which is the equivalent inductance of the crystal. In

> like manner, you can find the series C, since Xc = XL.

>

> And finally, the Q you wanted (the crystal's Q) is XL / Rs.

>

> Now you know about everything about the crystal and can get one of

> your Hayward or Demaw books and start designing some filters. Hayward

> has nice software for this in both Introduction to RF Design and

> Experimental Methods in RF Design, both from ARRL. If you want to

> include holder (parallel) C in your modeling, 5 pF is a good estimate.

>

> Jim Kortge, K8IQY puts his crystal in a 12.5 ohm environment by using

> 4:1 (impedance) bifilar transformers into and out of the crystals (50

> ohm attenuators are still used though, to assure known generator and

> load resistances). This has the advantage of making the resistance

> measurement easier, but it makes the loaded bandwidth smaller, so you

> need a good stable generator that you can read to the Hz. Those

> little DDS units are nice. Be sure to use filtering if necessary for

> signal purity. Jim designed a nice little VXO (variable crystal

> oscillator) that uses one of the crystals from the set you are

> measuring in the oscillator circuit. See it on NJQRP's page:

>

> http://www.njqrp.org/pvxo/index.html

>

> I followed Jim's lead but used resistive 50 to 12.5 ohm matching pads

> instead of transformers. That way I got rid of any reactive effects

> (which are minimal) of the transformers, but required a lot more

> driving power due to the loss in the matching pads.

>

> OK, that was probably more than you wanted to know. Hope I remembered

> this stuff right.

>

> 73-Nick, WA5BDU

> in Arkansas

Hi, Nick,

No, not more than I wanted to know at all. I'm quite happy to have this

level

of info.

Thanks for the detailed reply -- gives me something to mull over during the

holidays.

-vs-

Roy Lewallen

January 2nd 04, 11:08 PM

The W7ZOI crystal filter design and crystal measurement methods are described

in detail in _Experimental Methods in RF Design_, published by the ARRL and

available from numerous sources. It should be every serious experimenter's

library.

Roy Lewallen, W7EL

Tom Bruhns wrote:

> If you have access to old QSTs, you should be able to find articles

> about measuring crystal parameters. Look especially for things by Wes

> Hayward, W7ZOI. There's a fairly simple crystal-tester you can build

> to measure enough parameters to extract equivalent L, Cs, Cp and R, I

> believe. I 'spose someone will pop in with a more specific reference

> for you.

>

> Cheers,

> Tom

>

> "Virgil Smith" > wrote in message news:<3iNHb.504277$275.1417484@attbi_s53>...

>

>>I have a bunch of oddball crystals that I want to test. I know I can just

>>build up a generic oscillator to find the

>>resonant frequency, but out of curiousity I would like to

>>know the quality of the things, too.

>>

>>Anyone know of any neat ideas for measuring the Q of a

>>crystal?

>>

>>I would welcome any and all suggestions,

>>

>>-vs-

Roy Lewallen

January 2nd 04, 11:08 PM

The W7ZOI crystal filter design and crystal measurement methods are described

in detail in _Experimental Methods in RF Design_, published by the ARRL and

available from numerous sources. It should be every serious experimenter's

library.

Roy Lewallen, W7EL

Tom Bruhns wrote:

> If you have access to old QSTs, you should be able to find articles

> about measuring crystal parameters. Look especially for things by Wes

> Hayward, W7ZOI. There's a fairly simple crystal-tester you can build

> to measure enough parameters to extract equivalent L, Cs, Cp and R, I

> believe. I 'spose someone will pop in with a more specific reference

> for you.

>

> Cheers,

> Tom

>

> "Virgil Smith" > wrote in message news:<3iNHb.504277$275.1417484@attbi_s53>...

>

>>I have a bunch of oddball crystals that I want to test. I know I can just

>>build up a generic oscillator to find the

>>resonant frequency, but out of curiousity I would like to

>>know the quality of the things, too.

>>

>>Anyone know of any neat ideas for measuring the Q of a

>>crystal?

>>

>>I would welcome any and all suggestions,

>>

>>-vs-

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