Dave,
My comments are addressed to the following part of your post:
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!
- - - - - - - -
The description of your earthing configuration sounds very typical to that of
most hams I have spoken with on the subject. (Note: I was also a reviewer and
contributor to the ARRL book on grounding and bonding.) I have to agree with
you about the cost of doing a complete grounding and lightning protection
scheme for any station having more than a very few transmission lines. I
designed my installation back in 2001, using MIL-HDBK-419A as my guide (I am
retired from Rockwell Collins as an EMC engineer). I have around a dozen
coaxial cables, plus rotator and remote switching lines, each of which is
lightning protected. Yes, I could have purchased a decent transceiver for the
funds expended to do all of that.
In my case, there has been a big payoff for all of that effort: on June 8,
2008, my 100 foot tower (home to my VHF and UHF arrays) took a direct lightning
strike while I was using the antennas to handle emcomms related to severe
T-storms in the area. All of the equipment in the shack and, most importantly,
ME, survived the hit. (I was actually transmitting on 2m when the strike hit.
I was a victim of "near strike lightning" because the shack is about 50 feet
from the tower, which was conducting about 60kA [estimated by a Collins
colleague who was the high energy physics expert]. The coupled field did
produce a charge in my body; the charge discharged from my right arm to the
metal cabinet of the Astron power supply.)
The same tower took another hit in May, 2009. I was not transmitting at that
time, but all equipment in the shack and house escaped damage. I attribute the
lack of damage to the bonding of the RF system grounds to the house electrical
ground, thus eliminating the huge electrical difference between the two
grounding systems. Of course, antennas, coax cables, and other items mounted
on the tower were damaged in both strikes, but zero damage inside the house and
shack. Two of the coaxial line protectors were blown apart.
I'll conclude by saying that extensive grounding and lightning protection does
work, but cost is the big factor. Hams living in areas of high lightning
activity should, at the very least, consider observing proper grounding and
bonding techniques. If buying enough protectors is not economically feasible,
then thought should be given to disconnecting of cables when the station is not
in use.
73, Dale
WA9ENA
-----Original Message-----
From: David Eckhardt <davearea51a@gmail.com>
Sent: Jan 22, 2025 3:54 PM
To: <jim@audiosystemsgroup.com>
Cc: <rfi@contesting.com>
Subject: Re: [RFI] Common Mode Noise?
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.
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 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
> http://lists.contesting.com/mailman/listinfo/rfi
>
--
*Dave - WØLEV*
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