Dave,
These words of yours here
(especially those I highlighted in bold type) are so very true!
And, is something that I have been saying for decades now!
The MFJ-993BRT ATU had trouble finding a match on some bands when feeding a 34' vertical when there was a short coaxial cable between it and the antenna. Connected by a 2' wire it worked fine but connected by a 2' coax was not. It seems the shunt capacitance of the short, low-Z cable may be the issue into the non-resonant antenna. A balun between the ATU and the antenna adds a short low-Z transmission line. So, it could be better to connect your antenna ladder line directly to the ATU random wire and GND posts with a 1:1 CM choke on the input side of the ATU.
I know that some of the modeling experts out there can show models until the sun no longer shines, but the fact is the myth that you can feed a random wire antenna, with a coax (from a tuner) and not lose significant performance and/or not have tuning issues is something that I've been trying to propagate for many, many years (decades).
{ever since my first remote-tuner random-length wire antenna (a non-res vertical wire on a boat) install assist, as an adolescent, in 1973, I've been using GTO-15 wire (or other well-insulated / well installed wire) on the tuner output.....and, while we never saw anyone even attempt using "coax" until the past 20 some years, (when modern GPS, etc., gave many their easy entre' into offshore sailing, etc.), over the past couple decades I've seen many try to use coax out of an Icom AT-130/At-140 (or AH-2 or AH-4), etc....and simply replacing it with a length of wire (GTO-15 or otherwise), they see significant improvements in both their transmit performance and tuner's abilities....(....and surprising to many even improvements in rec s/n, mainly 'cuz they have RFI-producing devices within feet or inches of their radio, tuner, and/or antenna)....and, with the questionable tuning ability / lossiness of an MFJ tuner (torroids and cermanic caps, I think....rather than the air-wound copper coils and silver-mica caps of the Icom tuners), trying to use coax on the tuner output, can run into some serious issues...and, I think Alan, K0BG, has also found many HF Mobile installs trying to use coax out-of remote tuners, as well....and he always mentions this as a big mistake!}This is also why I try to point out to folks that placing a balun (or unun) on the tuner output (antenna terminals) is a bad idea!
And, try to recommend that they use a common-mode-choke / "line isolator", on the coax on the input (radio side) of the tuner....to keep the coax from radiating, etc...
Of course if using these single-ended tuners with balanced feeders on the output, some think this requires a "balun", but I've found this to be a mistake....use the tuner "output" and "ground" lugs to feed the open-wire-line and you're good as far as the antenna and tuner is concerned....
And, here again I try to recommend that they use a common-mode-choke / "line isolator", on the coax on the input (radio side) of the tuner....to keep the coax from radiating, etc...
Anyway, Dave, I just wanted to say Thank You for mentioning this here!Some folks get too wrapped-up in the "common-mode" issues that seem to propagate our ham discussions these days, they forget that the main role of the antenna system is to radiate the transmitter power as efficiently as possible / efficiently receive signals as exclusively from the antenna as possible....and, trying to feed the antenna with coax from these single-ended tuners and/or adding a "balun" or CMC on the output of a single-ended tuner to a non-res antennas is a very bad idea!
Fair winds Tim, and good luck to you on your antenna project (and yes, keep the choke on the input [radio side] of the tuner)
73,
John, KA4WJA
P.S. as for "adding an image"?
Easy-peasy...
Here is the inside of the Icom AT-140:
