Jim, far too many hams solidly believe open wire, parallel conductor XMSN
lines, radiates just because it isn't shielded. Absolutely wrong if care
is taken to keep the currents balanced and the phases opposite. They simply
do not understand nor want to take the time to understand the rank basics
of a transmission line, coax or open wire, or for that matter, G-line.
Nor do they understand that ANY amateur antenna like a dipole is
UNBALANCED. Period! Even Uncle most times can not assure that. As you
commented, the local environment dictates unbalance between the two sides
of a dipole, unless it's in free space..... How many of us absolutely
assure homogeneity for a couple of lambda below our antennas? I'll bet
none of us hams do, myself included. But I know how to build, measure, and
install common mode chokes and use them intelligently. Further, I have
never, except for the first three or so years I was licensed, "grounded"
(earthed) my station. Three kinds of earth connection: 1) safety (the
"green" wire), 2) ESD bleed dump, and 3) lightning remediation (not direct
strikes, but for radiated fields from near-by strikes). Also, realize the
typical amateur budget does not allow for protection against direct
strikes!
When Uncle installed the ported coax around the fissile material storage
facility on Kirtland AFB in Albuquerque, N.M., he spent millions and
millions of your and my tax dollars in preparing the surrounding soil.
Even then it wasn't perfect and quite problematic.
Yes, I use parallel conductor XMSN line for my HF wires (doublet),
exclusively, except for my vertical which is by design, unbalanced. Hams
don't get that, either! How many times have I read the question on a
number of sites, "Do I need a balun or common mode choke on my vertical"?
DDaaaaahhhhh......
Dave - WØLEV
On Wed, Jan 22, 2025 at 7:35 PM Jim Brown <jim@audiosystemsgroup.com> wrote:
> On 1/22/2025 10:43 AM, K9MA wrote:
> > The whole point of using coax is to prevent radiation until the RF gets
> > to the antenna. There's no need to further complicate the issue.
>
> There is no more or less radiation from a 2-wire line than from coax.
> What causes radiation is common mode current, and 2-wire can carry just
> as much common mode as coax of the total antenna system is unbalanced.
> Just as in coax, common mode current in 2-wire line shows up as a
> difference between current in the two wires, taking both magnitude and
> phase into account.
>
> Antennas can be unbalanced by their surroundings, like variable height,
> sloping ground, nearby conductive objects, imbalance in the termination
> of 2-wire line in the shack, including a poorly balanced tuner or
> matching network.
>
> 73, Jim K9YC
>
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>
--
*Dave - WØLEV*
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