In article , J M Noeding
writes
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
--
remove ,xnd to reply (Spam precaution!)
The butler type is a tuned amplifier were there is ideally zero phase
across the crystal and hence the crystal can be simulated by a resistor
of equal (in practise lower) resistance than the crystal loss.
Hence a butler tuned to 100MHz will oscillate a 50R resistor at that
frequency.
The 100MHZ crystal if 5th overtone will have a fundamental response at
approx. 20MHz and a 3rd overtone response at 60MHz .
The fundamental response (resistance) will be much lower than the 5th
resistance and in a zero phase amplifier with flat response the crystal
will preferentially oscillate at 20MHz.
Higher order overtones have the same C0 or stray capacitance as the
fundamental but this has a lower reactance at higher frequencies.
This is the reason and increase in resistance at higher overtones that
overtone oscillators get increasingly tricky.

--
ddwyer