[Elecraft] RE: In Shack Radials and Ground

[Don Wilhelm]

Jim,

In an ideal world, the tuner is only an impedance transformation device -
but the name of this RF Ground game is the elimination of common mode
current from the transmission line and equipment in the shack so that all
devices, including the tuner can work as expected with no extra RF floating
around.

The RF ground needs to be associated with the antenna system, thus connect
to the tuner (or whatever is to be connected to the antenna system).  The
transceiver does not need an RF Ground.

Most modern transceivers are designed to drive a 50 ohm coaxial load.  Plus,
the transceiver itself will not put any common mode current on the coaxial
line - all its energy is inside the coax as a differential output between
the coax center conductor and the inside of the shield - there will be no RF
energy on the transceiver enclosure or the coax shield that is being
generated by the transceiver.  So the bottom line is to keep the common mode
currents coming in from the antenna system from being coupled back onto the
coax shield between the tuner and transceiver.

The real proper place for the RF ground is at the antenna, so no common mode
energy is ever coupled back to the shack, but this is not a perfect world,
and in many cases, the RF ground must be placed at the shack end.  If there
is a tuner, the RF ground should be placed at the tuner output - EXCEPT, if
chokes or baluns are placed between the tuner and the antenna, then the RF
ground should be placed at the choke or balun.  In other words, looking from
the antenna toward the shack, place the RF Ground prior to any device that
attempts to eliminate common mode current from the remaining coaxial cables
and equipment chassis.  There must be a path for that common mode current to
flow, and the RF Ground is a proper place for it to flow - it will find a
path if one is not provided, but the one found may not be desirable.

73,
Don W3FPR

> -----Original Message-----
>
> Don,
>
> Seems we are in basic agreement.  I agree that the equipment termination
> point of the ground wire can be a subtle thing.  My preference
> would be at
> the actual point of generating the RF, i.e. the transceiver
> usually.  Here I
> go again, but my way of thinking is an antenna tuner is only an impedence
> matching device and has no direct relation to the length of ground wires.
>
> Jim, AB0UK
>
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