The Untuned-Tuned-40 (UT-40) 40-Meter Transmitter

The Untuned-Tuned-40 transmitter brings the 200-mW signal from my Crystalizer exciter up to 11 W output. No neutralization is required. The capacitance values in the output network are taken from a Radio Handbook table; the use of variable capacitors capable of swinging through those values is recommended. The bypassed-for-RF 100-ohm resistor in the final-amplifier grid circuit allows straightforward measurement of the final grid current, with 0.1 V across the resistor equating to 1 mA. Cathode keying (DX, driver; FX, final) is shown; at W9BRD I implement this approach across multiple transmitters by means of an outboard box that keys each stage with its own high-VDS power MOSFET. (KD stands for key down.)

Schematic diagram of the Untuned-Tuned-40 (UT-40) 40-Meter Transmitter

Revised November 21, 2015 CE. Copyright ©2015 by David Newkirk ( All rights reserved.