I know that one has to be careful that a suffucuent DC ground is
provided in addition to the RF ground. Otherwise high currents
can be drawn though the RF ground with bad results. I personally
have never heard of no grounding the radio to the RF ground. If
you look at the manual for most any HF rig you will see that it
requires an earth ground to a stud on the back of the rig. Seems
to me that connecting this to the RF counterpoise makes sense.

Doug, k3qt
s/v Callista

"Gordon Wedman" wrote in message
news:mYIuc.10643$ig5.6123@edtnps89...
The question was whether it was necessary to provide an RF ground for the
transmitter in addition to the RF ground provided at the ATU. I believe
the
answer is generally no.

Well as I mentioned previously, Icom's printed literature on
antenna/transciever installation recommends grounding the transmitter to
the
same ground ("boat ground") as the tuner using foil. Of course the Icom
tech that I contacted about this said not to ground the radio so everyone
is
confused about this..................

"Chuck" wrote in message
...
This addresses a question I thought I saw on this group not long ago. I
apologize for not being able to post this in a timely way. I also
apologize
if this information has already been posted.

The question was whether it was necessary to provide an RF ground for
the
transmitter in addition to the RF ground provided at the ATU. I believe
the
answer is generally no.

First, whether there is any direct connection between the transmitter
case
(i.e., the outer shield of the coax connecting the transmitter to the
ATU)
and the ground terminal at the output of the ATU is entirely
coincidental.
Well, not really coincidental. It would be better to say that such a
direct
connection is not required. A good many ATU designs utilize inductive
coupling to the transmitter, or to the antenna, and a direct connection
in
those cases is purely optional.

The common marine ATUs, however, rely on a form of L-matching circuit in
which there IS a direct connection between input and output "grounds".
And
so the transmitter case winds up being connected directly to the ATU
ground
terminal and, therefore, to the vessel's RF ground system, whatever that
might be.

We need to keep in mind that the proper functioning of an antenna,
tuner,
transmission line, and transmitter, whether on a boat or off, does not
require as a matter of theory that the transmitter case be connected to
RF
ground.

As a practical matter though, the transmitter and the transmission line
to
the tuner are both in the very near field of the antenna. This is
especially
true on a boat. RF from the antenna can travel along the outer shield of
the
coax, along microphone, speaker, and power cables and get back inside
the
transmitter with difficult-to-predict consequences!

Getting to the real point, now. So sometimes, we need to do things like
run
a copper foil (low impedance) RF ground connection from the transmitter
case
to the boat's RF ground system. Sometimes it will help, sometimes it can
make matters worse. Sorry. Also, the system is likely to behave
differently
at different frequencies. There are ways to test for these currents and
often ferrites can be used in the lines to choke problem currents.

Finally, caution should be exercised in relying on copper foil to
provide
lightning protection. It would vaporize like an old-fashioned fuse with
any
significant current flow. It would be fine, however, for draining off
charge
accumulations from masts and wire rigging.

Hope this helps.


Chuck