Again, thanks! I remember reading about that military project, forget
where. Great example!
The first times I encountered open wire line were either on a tour of
the Crosley VOA site by our senior EE class (U of Cincy), or maybe at AM
broadcast stations, where it is widely used and coaxial to feed
verticals. I've also seen that coaxial open wire line at commercial HF
communications RX and TX sites north of San Francisco.
73, Jim K9YC
On 1/22/2025 1:54 PM, David Eckhardt wrote:
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
<mailto: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
_______________________________________________
RFI mailing list
RFI@contesting.com <mailto:RFI@contesting.com>
http://lists.contesting.com/mailman/listinfo/rfi <http://
lists.contesting.com/mailman/listinfo/rfi>
--
*Dave - WØLEV
*
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|