[Elecraft] KX3 ATU

[Michael Babineau]

Niel / Robert :

For what it is worth,  86 feet (i.e 26.5 m) is the ideal length of end-fed wire for matching via an auto tuner to cover the HF bands.
It is a "magic length" that isn't  close to a multiple of a half wave on any of the HF bands (with perhaps the exception of 10m)
so it presents a reasonable impedance that can be matched by most ATUs across the HF spectrum.  As Eric mentioned,
you want to stay away from lengths that are close to a half wave multiple on the bands that you want to operate as the wire will
present a very high impedance that is difficult to match with any ATU. 

Not surprisingly, this length is not far off of the length of wire used for the W3EDP antenna (84 feet).

Michael VE3WMB