I have an unknown crystal I wanted to test for its frequency.

On qsl net I found a test circuit to do just that (I think it is basically a
broadband amp).
Initially when I hocked the circuit up on my breadboard the crystal seemed
to oscillate at around 27 MHZ.
Then I built the little circuit on a permanent board and now the crystal
oscillates at about 9 MHZ and at this point I start to ask myself what am I
measuring here. And what assures me that 9 MHZ is the fundamental?

I would appreciate if anybody could shed some light on crystal testing.

Uwe

Your first osc got an overtone and the second the fundamental of 9 MHz and
the the 3rd overtone is 27MHz. It could also be a lower frequency like 3 or
1.5 MHz so listen for these frequencies. The 3rd or other overtones are
slightly higher than an odd multiple of the fundamental!
hank wd5jfr
"Uwe Langmesser" wrote in message
...
I have an unknown crystal I wanted to test for its frequency.

On qsl net I found a test circuit to do just that (I think it is basically
a
broadband amp).
Initially when I hocked the circuit up on my breadboard the crystal seemed
to oscillate at around 27 MHZ.
Then I built the little circuit on a permanent board and now the crystal
oscillates at about 9 MHZ and at this point I start to ask myself what am
I
measuring here. And what assures me that 9 MHZ is the fundamental?

I would appreciate if anybody could shed some light on crystal testing.

Uwe

Generally, a crystal is a fundamental frequency below about 15 MHz...

Above that, the quartz crystal starts to be thin enough to make it
fragile and prone to being broken. There are ways to make a fundamental up
to a hundred MHz or so, but these are usually very expensive crystals and
pretty rare.

So, it is most likely that the 27 MHz was the third overtone of the 9 MHz
fundamental frequency.

===============

A broadband amplifier type of oscillator may have enough gain, and
perhaps a parasitic resonance or so to make it tend to run on an overtone
frequency. Generally, build a good circuit on a solid ground and keep the
feedback loop set up for low gain on the feedback.

Excessive gain in the system will tend to cause 'strange' results and
your experience is not all that surprising.

================

Given that Citizens band frequency crystals used to be fairly common, I
would guess this is what you have.



Jim Pennell
N6BIU

Your first osc got an overtone and the second the fundamental of 9 MHz and
the the 3rd overtone is 27MHz. It could also be a lower frequency like 3 or
1.5 MHz so listen for these frequencies. The 3rd or other overtones are
slightly higher than an odd multiple of the fundamental!
hank wd5jfr
"Uwe Langmesser" wrote in message
...
I have an unknown crystal I wanted to test for its frequency.

On qsl net I found a test circuit to do just that (I think it is basically
a
broadband amp).
Initially when I hocked the circuit up on my breadboard the crystal seemed
to oscillate at around 27 MHZ.
Then I built the little circuit on a permanent board and now the crystal
oscillates at about 9 MHZ and at this point I start to ask myself what am
I
measuring here. And what assures me that 9 MHZ is the fundamental?

I would appreciate if anybody could shed some light on crystal testing.

Uwe

Generally, a crystal is a fundamental frequency below about 15 MHz...

Above that, the quartz crystal starts to be thin enough to make it
fragile and prone to being broken. There are ways to make a fundamental up
to a hundred MHz or so, but these are usually very expensive crystals and
pretty rare.

So, it is most likely that the 27 MHz was the third overtone of the 9 MHz
fundamental frequency.

===============

A broadband amplifier type of oscillator may have enough gain, and
perhaps a parasitic resonance or so to make it tend to run on an overtone
frequency. Generally, build a good circuit on a solid ground and keep the
feedback loop set up for low gain on the feedback.

Excessive gain in the system will tend to cause 'strange' results and
your experience is not all that surprising.

================

Given that Citizens band frequency crystals used to be fairly common, I
would guess this is what you have.



Jim Pennell
N6BIU

Initially when I hocked the circuit up on my breadboard the crystal seemed
to oscillate at around 27 MHZ.
Then I built the little circuit on a permanent board and now the crystal
oscillates at about 9 MHZ and at this point I start to ask myself what am I
measuring here. And what assures me that 9 MHZ is the fundamental?

Uwe-

As has been pointed out, you probably have a crystal from an old CB set,
designed to operate on its third overtone. At one time CB sets were sold with
only a few channels. You purchased transmit and receive crystals for the
channels of your choice, to supplement the one that was supplied with the
radio.

How do you know the 9 MHz is NOT an overtone? The observation that crystals
usually only operate at an odd overtone, might lead you to believe this. For a
9 MHz overtone, the fundamental would likely be at 9/3, 9/5 or 9/7. There may
be odd multiples of these frequencies that fall near the observed 27 MHz
frequency, but they would be relatively high multiples.

One way to tell would be to incorporate tuning components to select a desired
frequency. If the crystal will oscillate with tuning set to 9, 27 and 45 MHz
but not at 3, 1.8 or 1.286 MHz, then it is reasonable to assume 9 is the
fundamental.

73, Fred, K4DII

Initially when I hocked the circuit up on my breadboard the crystal seemed
to oscillate at around 27 MHZ.
Then I built the little circuit on a permanent board and now the crystal
oscillates at about 9 MHZ and at this point I start to ask myself what am I
measuring here. And what assures me that 9 MHZ is the fundamental?

Uwe-

As has been pointed out, you probably have a crystal from an old CB set,
designed to operate on its third overtone. At one time CB sets were sold with
only a few channels. You purchased transmit and receive crystals for the
channels of your choice, to supplement the one that was supplied with the
radio.

How do you know the 9 MHz is NOT an overtone? The observation that crystals
usually only operate at an odd overtone, might lead you to believe this. For a
9 MHz overtone, the fundamental would likely be at 9/3, 9/5 or 9/7. There may
be odd multiples of these frequencies that fall near the observed 27 MHz
frequency, but they would be relatively high multiples.

One way to tell would be to incorporate tuning components to select a desired
frequency. If the crystal will oscillate with tuning set to 9, 27 and 45 MHz
but not at 3, 1.8 or 1.286 MHz, then it is reasonable to assume 9 is the
fundamental.

73, Fred, K4DII

Crystals will operate on a number of fo's.
I use three oscillators to test them and each gives a different fo.
Be careful and keep the drive level down as some oscillators can cause damage.
Bob
WA4NBI

in article , WA44NBI at
wrote on 12/7/03 9:33 PM:

Crystals will operate on a number of fo's.
I use three oscillators to test them and each gives a different fo.
Be careful and keep the drive level down as some oscillators can cause damage.
Bob
WA4NBI


I had to laugh when I read your post, it sort of reflects my experience, eg.
every experiment gives you new and unexpected answers.

And I thought it was only me...

Uwe

On Mon, 08 Dec 2003 05:10:02 GMT, Uwe Langmesser
wrote:


Crystals will operate on a number of fo's.
I use three oscillators to test them and each gives a different fo.
Be careful and keep the drive level down as some oscillators can cause damage.

I had to laugh when I read your post, it sort of reflects my experience, eg.
every experiment gives you new and unexpected answers.

And I thought it was only me...

Uwe

.....and it is better when you can laugh about it.... sometimes it is
difficult to understand why your xtal won't operate on a 3rd or 5th
harmonic when it seems to work for everybody else - and you specified
proper overtone xtal for the manufacturer,
But it is a lot of bad constructions!

In the butler-type xo (popular in UK) you may operate a 27MHz xtal on
45 and even 81MHz (believe it was DCoDA who first described it)

But I believe the original question was something else? Xtals testers
were so popular in the 60's when amateur run around to surplus stores
buying FT-243 xtals, and several such xtal testers are described in
CQ, Ham Radio, QST, 73 DL-QTC, QRV, CQ-DL, Electron and other, they
run on fundamental frequency using colpitts or pierce type oscillator
and measured grid current as measure for excitation

73
Jan-Martin, LA8AK
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