Rational Behind Large VXO Freq Swings…

Reposting here from my blog section on QRPedia – Mon, 02/22/2010, http://www.qrpedia.com/blogs/wb8icn

While cleaning up some old doc’s and notes last night, I ran across my copy of the 1999 FDIM Proceedings. George Dobbs3RJV had did a presentation detailing four small QRP projects for an evening or weekend, to include a Universal VXO (page 61 – 64). Reading through that article turned on a huge light bulb for me explaining why (or at least acknowledged that it is a reality and practical possibility to attain large swings) I was seeing a large swing on my 80 meter VXO project.

First of all, I love how George writes and speaks…a Master in His Own Time!  Anyway, George commented that DJ1ZB had wrote in one of the G-QRP Sprats that the in-series inductor with the variable cap and xtal in a VXO circuit can be improved by breaking up the inductor into two nearly equal value inductors to be laid side-by-side for interaction. This allows for interaction which in-turn produces freq swings well beyond the normal swing for a VXO. Nothing was said about using two xtals, which I did, so maybe there is a lot of promise in this endevour. I sit here watching yet another 5 to 8 inches of white rain coming down, so great day to snuff some VXO fumes and see how the following might be useful … or not.

1. Two xtals in parallel and series

2. Using molded inductors (so far that is what I have used), but then try wingding some roids to redo the test using ferrite/iron powder

3. Does the oscillator circuit, the use of a 2N2222A, or 2N4401, etc, makes any difference in the amount of freq swing

4. What is the drift, stability, and noise associated with a Super VXO

I have built up the VXO and buffer circuit used in the VRX-1 for experimenting with Wide Swing VXO’s.  I hope to start in the next day or two playing with different configurations of L/C/Xtal to find the most widest swing with stable and repeatable results.  George’s circuit looks interesting so might have to build that one also to see which is best.



2 Responses to “Rational Behind Large VXO Freq Swings…”

  1. WØLMN Says:

    Good stuff here … I would like to link my blog [w0lmn.wordpress.com] to your if OK.

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