RadioM1DLG

End-fed half-wave calculator

v1.0.0

EFHW starting wire length • horizontal, sloper or inverted-L mechanical layouts

01 Frequency & layout
02 Construction
03 Length adjustment

Main wire starts at half a wavelength × the length factor. The counterpoise entry is only a requested construction length; it is not a matching prescription.

This page deliberately does not calculate transformer ratio, feedpoint impedance or SWR.

DIMENSIONED LAYOUT

Your EFHW

Starting wire geometry only. Transformer, common-mode behaviour, counterpoise, installation and surroundings materially affect the finished antenna.

Formula, assumptions & accuracy

Main wire cut length = 0.5 × λ × the entered factor. Horizontal/sloper/inverted-L choices only convert that same wire length into mechanical extents.

The optional counterpoise is entered as a percentage of free-space wavelength. It is shown because builders may want a repeatable construction dimension; this calculator does not claim that a particular percentage is electrically optimum.

No transformer turns ratio, feed impedance, SWR, gain or radiation pattern is predicted.