[Heath] High-performance crystal-tester

[Kenneth G. Gordon]

On 19 Mar 2012 at 15:50, G3OOU at aol.com wrote:

> I use a Type 193a Crystal Activity Meter for fundamental parallel
> resonance crystals which dates back to WWII and does fairly well. 
> I have made several  attempts to do a solid state equivalent but none 
> work as well as the original.

I would certainly be interested in seeing a schematic of that Type 193A 
meter, Bob.

> STC in the UK made a series resonant test set many years ago but I 
> have never managed to get my hands on a circuit diagram.

I am somewhat surprised at the level of interest in my no-more than hinted-at 
"high-performance crystal-tester" comment. I thought I was the only one 
interested in such "old technology". :-)

What I have in mind is an instrument which will test for R, F, and Q, 3 db 
points of resonance (both series and parallel), and activity (parallel only at 
this point) for crystals over the range of 10 Khz (or so) through 25 MHz or 
more, including 3rd and 5th overtone, with a view to using some of these in 
crystal filters.

Besides that, it would be great fun.

Furthermore, I have an unusually good stock of crystals, both FT-241 (LF) 
and FT-243 types, in addition to the smaller, more modern types.

W1FB published a circuit and a device which will test for some of the above 
in QST magazine in January of 1990 beginning on page 21. FAR Circuits 
makes and sells a circuit board which is the heart of that instrument.

In order to test all crystals in the range desired, at least for activity, one must 
"band-switch" some of the components some where within the range, 
perhaps two or three times, but this is trivial.

I found many, many circuits over the past number of years which have been 
used to test crystals for activity, many of which use tubes. In this case, I want 
to use solid-state devices, and have found a circuit which looks very 
promising. I intend to use an FET which exhibits unusually high 
transconductance, something like 13K micromhos.

As soon as I have built the device and have had some experience with it to 
determine whether or not it meets MY particular criteria, if it does, I will then 
attempt to have an article published in ER Magazine about it. If it is not 
accepted for publication there, I may make it public domain.

vy 73,

Ken W7EKB