[Elecraft] how to optimize end-fed?

[Lynn W. Taylor, WB6UUT]

In my opinion, what you want is the lowest SWR on the feed line between 
the Balun and the tuner.

The higher the mismatch, the higher the feedline loss.

Let's say you're operating on 14.300 MHz, and your wire is roughly 9.85 
meters (32' 4") long.

If I did the math right, that's pretty much exactly 1/2 wave, and the 
impedance at the feedpoint (the end) is near infinity.

Your 16:1 tap might be good enough to bring that into the ATU range.  
The SWR would likely be high.

Make the wire a bit longer (to get away from the exact 1/2 wave) and the 
impedance comes down.

At some point, you'll get a better match (lower SWR) on the 4:1 tap than 
the 16:1 tap.

For some wire lengths, the 1:1 tap will give the lowest SWR between the 
tuner and the wire.

I'll be honest and say that I don't know how the inductance in the tuner 
is related to SWR.

If you trim the wire so that the impedance is 800 ohms (16 times 50) and 
use the 16:1 tap, the SWR between the UNUN and the Tuner should be 1:1, 
but we're no longer talking about "random" wires.

I'm sure those who invoked The Hitchhiker's Guide to the Galaxy were 
trying to point out that, without getting into a lot of specifics, it's 
hard to answer.  That's why I picked 14.300 MHz -- to make the question 
far more exact.  Humor doesn't always translate, however.

Stay on 14.300 and make the wire three times longer, and the discussion 
stays the same -- instead of the wire being 1/2 wave long, it's 1 1/2 waves.

Move to 7.150 and double the length of the wire, and the discussion 
stays the same, only the lengths change.

This page <http://udel.edu/~mm/ham/randomWire/> talks about "random" 
wires, and the lengths that do fall near an odd multiple of 1/2 wave.  
Staying away from these lengths makes the tuner's job easier.

I'm also ignoring (on purpose) how well the antenna radiates.  It seems 
to me that if the power doesn't get into the antenna, it doesn't much 
matter.

I'm sure we'll now hear suggestions from those who think another type of 
antenna is better, but your original question is the same with a miscut 
dipole as it is with a high-impedance end-fed wire.

73 -- Lynn


On 10/1/2016 7:26 AM, Holger Schurig wrote:
> My question was really: is it desirable to always aim for the lowest
> inductance of an ATU tuning.  AFAIK this question is totally independent
> from the wire length. If anything, I'll optimize the wire length to make
> this happen ... or I won't care if my thesis is all bogus.