[Elecraft] how to optimize end-fed?

[Logan Zintsmaster]

I just finished typing up the pretty much the same answer.  Should have
gotten up earlier.

To add to Lynn's comments, setting the balun tap to the lowest SWR means you
are minimizing the work that the
tuner has to do and as a result probably minimizing it's losses, as well.

So to summarize...

1.  Bypass the tuner and select the balun tap that gives you the lowest SWR.

2.  Activate the tuner and enjoy lots of QSOs.

Logan



-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Lynn
W. Taylor, WB6UUT
Sent: Saturday, October 01, 2016 9:27 AM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] how to optimize end-fed?

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.

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