On 2/20/2016 10:29 PM, Jim Brown wrote (in replying; single bar) :
Can I attach my radial system (which I would disconnect from the copper
pipe driven into the ground) to my L-network coupler and ISOLATE THAT
COUPLER FROM GROUND WITH A BALUN?
That is a bad idea.
That would separate the RF ground from the Shack (lightning ground).
That's also a bad idea. Remember that lightning is NOT a DC event, is
an RF event, with peak energy broadly centered between about 100 kHz
and 10 MHz. A radial system provides capacitive coupling to the
earth, so if it's part of the building ground, it lowers the impedance
to earth, so it improves lightning protection.
Second, there is no such thing as RF ground. For decades, we have
heard the same nonsense from the high-futility audio world about
separating the "clean audio ground" from the rest of "ground," which
is "dirty." Separated grounds are a really bad idea, especially at
RF. Now, we DO use "isolated ground" wiring in power systems in
buildings to minimize circulating noise currents on sophisticated
technical systems, but every part of those systems IS grounded and
bonded in a very well controlled way, and all grounds are ultimately
bonded together.
It's an interesting discussion.There is often a good reason to isolate
an unbalanced antenna from the shack. IIRC, AM broadcast stations often
use an air core transformer, with spacing adequate to allow lightning
protection to fire and not arc to the transmission line.
I suspect that a tank circuit at the antenna tuner output, connected to
the radials, could provide the LF steering needed to drain static there,
and send tuner return current RF to the radials. I used a shunt
inductor in my mobile station, allowing easier matching to the low
impedance of a 5 foot mast, loading coil, and whip, and on higher
frequency bands [with the tuner in the trunk, eliminating precipitation
static that would sooner or later have blown out the tuner -- or the gas
protector in a transceiver.
It probably doesn't need saying that a connection to the house ground
need not run to the station. It can go directly to the ground at the
power entrance.
Cortland, ka5s
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