2-BAND VFO FOR 80 AND 40 METERS

This project assumes you have built a functioning Simplest Ham Receiver and can solder components to a circuit board. Adapted from a schematic diagram in the 1993 ARRL Handbook, this VFO permits continuous user-selected tuning-range portions of about 50kHz on the 40 meter band and 30kHz on 80 meters. There are MANY designs possible, but this one was chosen because:

-- it uses the same power supply as the receiver (6-8V);

-- it demonstrates use of bipolar transistors as varactor diodes, which enables a simple cheap potentiometer to be used for tuning instead of a hard-to-find and probably expensive variable capacitor;

-- frequency range is easily changed by merely adjusting slugs on coils;

-- instead of two bands, covering larger portions of a single band is easily done; and

-- it's buildable and it works.

Decimal capacitance values are in microfarads (uF); whole-number capacitance values are in picofarads (pF or uuF).

Most general-purpose transistors will probably work in this circuit instead of those shown; back-to-back diodes can of course be tried instead of the 2N3053's.

L1: 4.6-8.5 uH adjustable RF coil (Miller #23A686RPC).
L2: 2.4-4.1 uH adjustable RF coil (Miller #23A336RPC). Miller #23A226RPC will also work.

Above coils are available from Circuit Specialists; another option that works well for L1 is the Miller #4204 5-12uH Adjustable RF Choke available from Ocean State Electronics. S1: DPDT miniature toggle switch.