WHEN A Novice graduates to a higher-class license, he wants to take advantage of his new privileges as soon as possible, including the use of a variable-frequency oscillator. A VFO will permit the operator to control his transmitter operating frequency without investing in a bank of crystals. Most of the beginners' transmitters use tubes, and the first stage of such a rig requires 15 volts or more drive from a VFO. The solid-state variable-frequency oscillators described in ham publications have a number of outstanding features, but have only one or two volts output - not nearly enough to drive a tube-type transmitter. The unit shown in the photographs is based on a collection of proven circuits from past QST articles.1 It is possible to use the VFO as an 80/40-meter QRP transmitter. As such, it will deliver up to 2 watts into a 50-ohm load by omitting the output impedance-matching transformers. In a trial, the VFO was keyed by breaking the 13-volt lead from the power supply. Surprisingly, no chirp resulted. The daring may wish to try this approach, but a keying filter should be added to prevent clicks. Those interested in a QRP VFO-controlled rig, however, should add a second buffer stage such as shown in "Once More with QRP" (QST, August, 1970).
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