[Elecraft] how to optimize end-fed?

Sat Oct 1 14:41:46 EDT 2016

Holger: Your English is fine! 

Anything your internal KX3 ATU can match it will match with good efficiency.

Allow me a couple of observations that might help.

Your assumption about low L is correct since, in any well made matching
network, the greatest losses are when high circulating RF currents flow in
inductors and result in resistance losses in the wire. In many modern
miniature inductors using toroids, those currents can actually cause strong
enough magnetic fields to "saturate" the torodial core, causing it to heat
and consume more power. In the extreme, the core may crack. And heating the
toroid may cause it to reach its Curie temperature where its magnetic
properties change dramatically, which changes the inductance of the toroid.
In operation, that may appear a a sudden large change in the SWR after
transmitting for long enough to heat the core. 

"L-networks" such as Elecraft uses are very high efficiency matching
networks. 
Other popular networks you will find used by Hams, such as the "T" network,
may have wider matching capabilities but can produce very high losses as
well.

All passive elements, such as a coil, have some losses. So I avoid any extra
elements that aren't necessary. 

If you are feeding your antenna wire directly - it is connected directly to
the KX3 I'd not use an external coil unless the KX3 cannot find a decent
match (by decent I mean 2:1 or lower). 

If you have a transmission line between the KX3 and the antenna you need to
consider the losses in the transmission line, especially if it is a
low-impedance line such as 50-ohm coaxial. If the transmission line is not
terminated at the antenna in its characteristic impedance (e.g. 50 ohms for
common coax) there will be standing waves on the transmission line. Those
standing waves will produce areas of high currents flowing in the
transmission line and result in losses due to resistance in the wires. In
that case you can reduce the total losses by matching the transmission line
to the antenna impedance at the antenna. The KX3 may be able to match the
antenna, including the transmission line, to the KX3 but that won't reduce
losses in a mis-matched transmission line. 

73, Ron AC7AC

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Holger
Schurig
Sent: Saturday, October 1, 2016 7:39 AM
To: Fred Jensen
Cc: <elecraft at mailman.qth.net>
Subject: Re: [Elecraft] how to optimize end-fed?

2016-09-30 21:59 GMT+02:00 Fred Jensen <k6dgw at foothill.net>:

> This is reminiscent of one of the five volumes in Douglas Adams' 
> trilogy, "The Hitchhikers Guide to the Galaxy."

I understand that either my english is very weird. Or that I can't explain
things good.

But that you and Davidthink that they must make a 42 joke on this is
definitely weird.

The question was: I can query the KX3 ATU for what it settled. I have an end
fed antenna and so I have various variables:

- used tap (1:4, 1:9, 1:16)
- some random length wire
- band

And forget an "optimal wire", I might just have switched from 12m to 10m.
Or back. Depends on what I find, propagation ...   so assume that my wire
is just some random wire, not necessary optimal for the band. And also, in
the context of my question, this is entirely irrelavant. I was never asking
about wire lengths, this is easy to read up. Okay, back to my scenario: I
just switched the new band. I'm not going to let my portable glass fiber
down because of that and change the wire length! Instead I do what a lazy OM
does: I press the TUNE button and the internal magical antenna tuner does
it's job. It's actually so magic, that it will do it's job on all taps. On
the 1:4 tap, on the 1:9 tap. And on the 1:16 tap. Woah! But I can query the
ATU for what inductance and capacitance it used to do the match.
And so my simple question was: would a lower inductance have less losses
inside the ATU?

And please: if you don't know the answer of if you think that there is no
answer, than just stay silent.

73, Holger
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