This page is Under Construction; updated on 12/14/2023
This page attempts to provide a collection of VFO designs that have been found over the years. There are hundreds of articles about VFO design and not all can be presented here. The ones on this page seemed most useful, in particular, to those who would build their own. As I find them, I’ll add more designs. Please send me your favorites!
Frank Harris’ book “Crystal Sets to Sideband” has much information concerning the design and stabilization of VFO’s. It is definitely worth a read if you contemplate building one.
Some will say that tube-based VFO’s are drifty and won’t stay on frequency long. To them I will say that my 80 year old LM-8 and BC-221 Heterodyne Frequency Meters (a.k.a. Oscillators) are as stable as a rock after about a 20 minute warm-up. I can set them on frequency, come back hours later and there they are, right on frequency.
VE7LCG has recently provided an article describing an analog solid-state vfo for a wide interval of frequencies. The lead-in to his article follows: “I was looking for an analogue oscillator for my receiver and transmitter projects. This VFO was supposed to complement my Arduino signal generator, based on a Si5351 and Arduino Nano. I just wanted to try the projects with the digital signal generator first, but also to be capable to show in function the same projects with a classic kind of VFO, something analog, stable…”
VE7LCG’s design is reminiscent of an old cathode-coupled (tube) design by VK3GU, published by VK3AT in the June, 1948 issue of Australia’s Amateur Radio magazine. The EF50 tube used after the cathode follower is unobtanium now so it would have to be changed to a different pentode. Have a look at both designs and roll your own!
Homebrew Digital VFO This modern design, by AA8V, is well described in the linked web page. It was originally included in the January, 2014 edition of QST magazine and is very well described on his web page.
A Simple Class E VFO for 160 and 80 meters. This design produces a two-phase output so it can be used for either single-ended RF finals or for push-pull output schemes.
The Vackar VFO, first proposed in the late 1940’s, probably does not get the attention it deserves. It has a very wide usable frequency range; about double that of a Clapp circuit. It’s easy to build and is very stable. The link provides a simple tube example and there are many solid-state designs on the web.
Here is a Wickipedia description of how the Vackar works.
Ham Radio magazine had an extensive article on the Vackar VFO and you can read a copy here.
The September 1978 QST magazine also described this VFO in an article. Read that here.
Googling “Solid State Vackar VFO” will provide a plethora of other designs – happy hunting!
The output of some VFO designs might need to be amplified to drive a particular transmitter. This ARRL article shows both a solid-state and a tube-based design to do the job.
Note that, when building a VFO that does not have a digital frequency readout, an inexpensive Chinese frequency counter (about $10) can be added and built right into the front panel of the VFO. Neat!