[Elecraft] how to optimize end-fed?

[Mel Farrer]

Fred said it right,  

Let me go to another side of the question.  No auto-transformer can match all of the antenna reflected impedances,  but using a parallel tank circuit to ground CAN.  The beauty of this arrangement is that you can tap the coil on the input of the coil and tap the output for a VERY wide range of impedance.  R and j .  What seems to have been lost in the transition from ancient and now is that we did not have ATU's.  All of the PRE now used tuned circuit match boxes.  Now you have to think about it for a few minutes.
Let me explain, the tuned parallel tank circuit can do a wide range of matching BECAUSE, If you tun the tank to one side of resonance your get a negative reactance,  if you tune it to the other side you get positive reactance.   HUMMMMMMM.
If the tank circuit is a true resonant one, the impedance across the coil from top to bottom is a range of the impedance available from HIZ to ZERO.  This is the beauty of the parallel tuned circuit over a auto transformer.  Oh well at least I remember it.....
Mel, K6KBE




      From: Fred Jensen <k6dgw at foothill.net>
 To: elecraft at mailman.qth.net 
 Sent: Thursday, September 29, 2016 1:57 PM
 Subject: Re: [Elecraft] how to optimize end-fed?
   
> Am I right to assume that the ATU settings with the lowest L is
 > always the best?

I don't know exactly what you mean by "best," but you said "always" so 
I'd say no.  If the length of your wire is in the vicinity of n * 90 
degrees where n is any odd integer, it will have a low-ish impedance at 
the end and 1:1 would be appropriate [if your UNUN had it].  If the 
length is around 180 degrees [or any integer multiple thereof] it will 
exhibit a fairly high impedance.

How long is the wire?
What band?

If the 1:4, 1:9, and 1:16 that you quote are turns ratios, the impedance 
transformation equals the square of them.  12,800 ohms and a 16:1 turns 
ratio yields 50 ohms.  12 Kohms likely exceeds the impedance at the end 
of a half-wave by quite a bit.

The Elecraft ATU losses are very low unless you're trying to match some 
outrageous impedance at the end of or beyond it's useful range.

73,

Fred K6DGW
Sparks NV USA
Washoe County DM09dn

On 9/29/2016 12:50 PM, Holger Schurig wrote:
> Hi all,
>
> I have an end-fed antenna with some random wire. The UNUN at one end of it
> has three sockets to plug the random wire in: 1:4, 1:9 and 1:16.
>
> My KX3 has the built-in ATU.
>
> I now want to find out on which band I best use which one of the sockets.
> As a first step, I wrote a simple program kx3lc.py (see
> https://gist.github.com/anonymous/5d53f5bdbc50782a9d5e2c8d7062be69) that
> can give me an output like this:
>
> holger at laptop:/usr/src/afu/kx3/swr$ ./kx3lc.py
> L: 0.12 mH,  C: 203.0 pF on transmitter side
>
>
> Am I right to assume that the ATU settings with the lowest L is always the
> best?  So when I have (for the three sockets), these values,
>
> L: 0.12 mH,  C: 203.0 pF on transmitter side
> L: 0.0 mH,  C: 246.0 pF on transmitter side
> L: 0.0 mH,  C: 256.0 pF on antenna side  (but lowest SWR 1.2-1)
>
> ... that the middle socket is the best?
>
> 73
> Holger, DH3HS

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