CRYSTAL TESTING CIRCUITS

In my previous job is a Radio Communications Engineer, and I wasresponsible for the servicing of Public Mobile Radio's, and over the years I have collected a reasonably large collection of Crystals from radio's which have had to be moved in frequency.

I decided it was about time that I checked out the fundamental frequencies of these crystals, they are mainly marked with either their overtone frequency or their final multiplication frequency. So I put together the following circuit and I would like to pass it along to those who may be interested.

Simply feed the output into a Frequency Counter, and place the xtals across the Xtal Pads. Using this circuit and a reasonable counter you can measure the fundamental frequency of any crystal to a resolution of 1hz, its ideal for matching crystals for use in Rx Filters.

Whilst looking through some back issues of SPRAT, I came across a similar circuit by G8DSO, Chris Warwick. His circuit will provide you with both the series and parallel loading frequencies.

Alternative transistors are 2N2222A or BC108