Precision VXO for Crystal Characterization & Matching

Posted on Feb 6, 2014

The Precision VXO (PVXO) and its matching Crystal Test Fixture (CTF) were created to provide a low cost means of evaluating the characteristics of crystals and a means of measuring their series resonant frequency. With this information, one can then build very low cost, high performance, crystal filters for receivers and transmitters. The PVXO was

Precision VXO for Crystal Characterization & Matching
Click here to download the full size of the above Circuit.

kitted by the NJ QRP Club, but has since sold out those units. However, photos of that unit are available on this page for completeness. The schematic diagram for the PVXO. A detailed description of what this circuit is and how it works can be found in the Atlanticon 2002 paper entitled "Simplified Tools and Methods for Measuring Crystals" whose link is at the bottom of this page. The circuitry shown above is transformed to a working instrument using Manhattan-style construction. The front panel contains the frequency control potentiometer, inductance switches, and the output BNC connector. Later on in the development of the instrument, the Arizona QRP Club offered their inexpensive "Stinger Singer" CW frequeny readout designed by Dan Tayloe, N7VE. This module was added and the instrument could now read out the frequency to which it was set. A SPST push button switch was added to the front panel to control the module. The NJ QRP Club sold 100 of the PVXO kits during 2002 and 2003. This picture shows what the finished kit looked like. Included were all components, case, and templates for doing the lettered covers. This kit was relatively expensive to produce due to the cost of the components, especially the precision 10 turn pot, five switches, and case, and therefore didn`t sell very well. However, those that bought them got a real deal considering the capabilities of the unit. This is a spectrum plot of the PVXO with a 4....

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