A mini tuner for EFHW antennas (true half wave)


If in a previous post I recommended that you omit the designations 64:1 and 49:1 in your diagram, I was afraid that you might not fully understand the function of the circuit used. That actually seems to be the case now.

No problem, just consider the primary winding as a coupling loop for the tuned parallel resonant circuit, formed by the secondary winding and the variable capacitor. What is required here is the well-known Thomson oscillation equation, ok.
BTW, to achieve maximum efficiency with a multi-band coupler, both the degree of coupling (number of primary turns) and the parallel resonant circuit (capacitance AND inductance) would have to be variable, because both are frequency-dependent.
Note: Due to the load of a connected EFHW antenna, the parallel resonant circuit is of course slightly detuned, but can easily be brought into resonance with the variable capacitor.

BTW, Doug DeMaw W1FB did a pretty good job of illustrating his explanation of the subject, didn’t he?
QST April 1985, Resonance and Tuning Methods

Hello Heinz,

you see? I’m still far away and need to study a lot more.
Thanks a lot for your information and the attached file. It helps a lot to understand what is going on with this coupler.

73 de Ignacio