I submitted this coax cable as a way to work effectively where your
ground wire is longer than a few feet a number of times on different
reflectors over the years. It is especially useful for those with second
floor stations.
Using a shield cable for an isolating DC ground is something I learned
many years ago when I was a practicing RF Engineer. Without getting into
the crazyness of it all... what this does as a circuit is to basically
take advantage or the 'skin effect' property of a conductor carrying RF.
RF radiated from the antenna system is picked up on the shield of the
coax ground and then travels along the outside skin of the shielded
cable (use good quality cable here). As a circuit the RF travels toward
Earth ground. Due to the skin effect of the shield the coupled RF energy
does not penetrate through into the inside conductor so RF is
effectively shunted to ground. Meanwhile the inner conductor acts
primarily as a DC ground regardless of its length (within reason) which
is its intended purpose.
Years after first learning about this I experimented with mix 43 ferite
beads placed at the open end of the coax shield at the shack end of the
circuit. If you want to add the ferrites you will probably want to use
at least 10 or more spaced an inch or so apart. You want to create a
very high impedance. Remember, the ferrites go at the shack end of the
ground and the center and the shield conductors are connected together
to a good ground rod while only the center connector is used in the
shack. I further recommend the ground connect to a single point and then
fan out to the essential equipment. I know this is going to bring up a
lot of discussion. Anyway, if you use an antenna tuner then this would
be the best place to connect this shielded ground.
For the person who suggested that a good operator doesn't need a ground
in their station (something to do with "what is that terminal for on the
back of a Triton IV)..... have you ever heard of 'near field' effect of
a transmit antenna? Do you know how far out the near field extends say
on 80 meters? Say on 20 meters? 10 watts? 100 watts? 1500 watts? Few
hams can install their equipment at such an impractical distance to get
outside the near field (which is really an RF hot spot) nor install
their shack in a grounded RF shield room. Anyway, the primary purpose of
the ground is safety, although receivers work better (quieter too) when
the rf front end has a completed RF circuit for the minute antenna
currents to flow through. This requires a good antenna and a good Earth
ground. Basic AC electrical theory here.
73,
Jerry, KG6TT
Fairfield
--
Ralph Jerald "Jerry" Volpe
Amateur Radio Operator KG6TT
ARRL Member & VE
FISTS 12304
788 Chestnut Drive
Fairfield, CA 94533
kg6tt@arrl.net
510 325-7724
707 399-8838 FAX
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