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[TowerTalk] Holy Grail [was: Common-mode current on feed line]

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Subject: [TowerTalk] Holy Grail [was: Common-mode current on feed line]
From: (Chuck Counselman)
Date: Thu Jun 26 14:34:32 2003
By "Holy Grail" I mean a

* no-tune,

* all-HF-band, and

* full-legal-power (incl. negligible-loss)

antenna-feedline system.  -W1HIS.

Dennis, K7FL, wrote:
>>[Chuck, W1HIS] was able to find one _fixed_ setting of the tuner 
>>for which the SWR on the coax (and therefore the loss) was 
>>tolerably low across _all_ HF bands 80 through 10 meters....
>This is a highly intriguing idea, so simple in concept (albeit 
>difficult in execution) that I'm surprised it isn't referenced in 
>more literature. I have a situation that just begs for this. 
>[Description snipped.]
>All these seem like a lot of variables. I was going to look for the 
>magic horizontal lengths in EZNEC to balance pattern with 
>impedance.... But as I said, this looks like a host of variables to 
>juggle - could there indeed be a methodical approach to this 
>Thanks Chuck - very interesting thread
>Dennis, K7FL

See the response to Howard K2HK that I posted a half-hour ago.  I 
suggested using Microsoft Excel for the simultaneous multivariable 
optimization, because (1) Excel has such an optimization capability; 
(2) probably most hams have Excel; and (3) Excel does complex 
arithmetic, so formulas representing transmission lines, simple 
lumped-element networks, and series- and parallel-connected 
impedances and admittances are easy to code.  I've written Excel 
macros even for _lossy_ transmission lines -- complex hyperbolic 
functions and all.

I don't know how to model an antenna accurately in Excel.  That's one 
reason why I wrote that I needed accurate antenna feedpoint impedance 
_measurements_.  Another reason is that, even with the best available 
antenna modeling programs (I use NEC-4) it's difficult to calculate 
feedpoint impedance very accurately.  With care you can come close, 
but probably not close enough reliably to design a matching system 

Thus, in my view, the chief unsolved problem is that of accurate 
antenna feedpoint impedance measurement.

73  -Chuck.
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