Here is a little project to help facilitate our field day operations and give us a portable random wire or doublet tuning with 100 watt capability. The L-Network Tuner was chosen to give a simple and efficient solution with the bonus ability to switch the capacitance to the input or output given a low or high Z load. An inch and a half diameter inductor and 150 pf variable capacitor fit nicely into a re-purposed computer monitor A/B switch box.
The inductor was tapped every 4 turns to give 12 increments of approximately 1uH each. Surprisingly 12 uH seems to be adequate range to tune most anything I have tried to date on 80-10m including an End-Fed L with a small counterpoise, random wire, near resonate dipoles and verticals... although I have not tried to shunt load any towers or chain link fences to date. . I provided both BNC, UHF and Wire outputs for flexibility. I can also use the extra outputs to add in additional capacitance if needed.
Tuning is fast and easy using the transceiver's VSWR meter, with most antennas needing the variable cap on the antenna side of the inductor. The small package is convenient to throw in a pack for use on the go.
KD4RAA
