[Antennas] How important is the ground?

Sat May 21 21:20:34 EDT 2005

Jack,
 The way I read David's message, he clearly states that the ground goes
back to the "same" ground as the electrical system. Since most 12V radios
do not have a 3 prong outlet connected to them, it is prudent to connect the
case to the electrical ground in some other fashion.
 You also miss the point of an RF ground. Yes, for safety, it must be
bonded to the main electrical ground. However, for a good RF ground, you
need a short low impedance path, which most electrical grounds are not. At
my station, a copper plate is the main ground "point" close to the station.
It is bonded with #6 back to the water main where the rest of the electrical
system connects. However, there are additional ground rods and connections
running radially from that plate outside in a number of directions,
including the antenna towers. Ground connections must be considered
"systems" and all must be bonded for electrical safety.
 At field day, each station gets a ground rod as close to the rig as
possible connected to it with flat braid or an old piece of coax. All of
the stations rods are then bonded to the rod at the generator with #6 solid.
 I learned the hard way what an RF ground means. Have you ever been
"burned" by RF from touching the case of a transmitter that did not have a
"low impedance" ground?
Mike, W1NR
-----Original Message-----
From: antennas-bounces at mailman.qth.net
[mailto:antennas-bounces at mailman.qth.net] On Behalf Of Jack Painter
Sent: Saturday, May 21, 2005 2:18 PM
To: antennas at mailman.qth.net
Subject: RE: [Antennas] How important is the ground?
David wrote:
There are 4 different purposes for a ground connection to a radio.
1. electrical safety. This only applies if you are connected to a power
source that may seek to get to ground through the radio. i.e. a commercial
AC main, or a generator that is properly grounded. If you run a charger on
the battery while you are in the house you should have a ground connection
that ties the rig case back to the same ground as the electrical system for
your safety.
--
That's just not correct, David. It's advice so old that it goes back to
before there was a fault-clearing design of all modern circuit breakers.
Since that time, it has been counterproductive to ground the case of any
three prong AC powered electronic device. In fact in the case of separately
grounded radio stations as many of us have, the NEC and NFPA required bond
from the radio station single point ground to the home's AC service main
ground is the ONLY thing that will save your life.
Ground rods do NOT, EVER protect your life in the event of equipment faults.
Earth's impedance is far too high to protect from electric shock, and there
is no way that using earth as a return circuit to the circuit breaker will
ever clear a fault.
Best regards,
Jack
Va Beach
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