[Elecraft] 270 foot (ish) Doublet & K3 ATU

[Wes (N7WS)]

My apologies for confusing two different posters to this thread.  Partly a 
consequence of threading and me using two different computers and two different 
email clients.

I want to specifically address this:

Rick claims that when using a series connection of two different transmission 
lines, one coaxial, one window line, changing the length of one (coax) affects 
something or the other, while changing the length of the other portion (window 
line) has no effect whatsoever.

This is clearly impossible.  I suggested earlier that one possibility is 
common-mode current on the coax that is confusing the instrumentation.  Just 
because a choke is applied doesn't mean that it is actually effective.

Rick should not be faulted for assuming that the window line is "low loss" while 
the coax is not. I have been trying to debunk this myth since 1993 when, "The 
Lure of the Ladder Line" was published in QST.  At that time, I had lots of 
(snail mail!) correspondence with then Antenna Book editor, Dean Straw, about 
this.  I pointed out that the chart of line loss vs. frequency that had appeared 
in every ARRL Handbook and Antenna Book since antiquity was wrong (easily noted 
by inspection).  We collaborated on a revision of this chart and I was invited 
to write something about balanced line use.  See: 
http://k6mhe.com/n7ws/Ladder_Line.pdf  published in the ARRL Antenna Compendium 
Vol 6.

I should mention that during this correspondence I pointed out that tuner and 
balun losses should not be ignored because they could be as detrimental as line 
loss. I had access to Touchstone, an early professional circuit analysis 
program, and gave examples of (IMHO) excessively high tuner losses that resulted 
from low Q components and the misadjustment of Tee type tuners. (Regrettably, I 
don't have copies of these letters any more.) After doing so, a QST favorite 
author, Frank Witt had a two-part article about tuner losses published in the 
April and May 1995, QST.  (I wasn't invited to write this one)  This month's 
"Hands-On Radio" column in QST brings up these losses again.

Straw wrote the program TLW, bundled with the ARRL Antenna Book, which (again) 
underestimated window line loss.  ARRL has just admitted this and offered a new 
version that allegedly fixes the problem.  (I don't know, I don't have a new 
enough version to qualify for the update, and I wouldn't use it anyway.  AC6LA's 
programs (ac6la.com) are superior and highly recommended.)

Sorry to ramble on this somewhat off-topic thread but I think this is worth 
mentioning.

Wes  N7WS

  On 5/15/2014 12:54 PM, Rick Bates, WA6NHC wrote:
> [snip]
>
> The coax portion of the feed should be as SHORT as possible, in my case it is currently about 10' (2.8 meters).  The losses are highest there and the extreme SWR makes it MUCH worse, keep it short; use the best stuff, not the cheap stuff.  Changing the length of the coax portion has a HUGE impact on where (or if) the system tunes; the window line, none.