[Elecraft] RF Ground (WAS: KAT100 on 30 Meters)

[Don Wilhelm]

Jim,

Well said - for years now I have been trying to convince folks that there is
a strong need for considering 2 'grounds' at a station.
The first is the Safety Ground which should be a low impedance path to
earth - large conductors, lots of heavy guage wire buried in the earth and
ground rods, and this must also be connected to the utility ground.
Properly implemented it should serve a a lightning protection ground.

The second is the RF Ground - and the Safety Ground may or may not suffice.
Consider a good Safety Ground with an 8 foot connection from the antenna
connection at the tuner - that combintion will likely produce a high
impedance for RF at 10 meters, thus there will be no RF Ground at that
frequency.  In such conditions, the use of quarterwave counterpoises for
each troublesome band is in order.

73,
Don W3FPR

-----Original Message-----

So what?  The significance of an RF ground is highly
overemphasized. Park next the to end of the runway of your local
airport and watch the 747's take off. Call me collect when you see
one trailing a ground wire. Last I heard, the onboard electronics
and radios work just fine without one.

The earth is NOT a sump into which noise is dumped, nor will a
connection to earth make a radio more stable. An earth connection
has no beneficial effect on the operation of a radio transmitter,
nor on the elimination of RF interference. In fact, a connection
made to earth by a noise source or receiver will act as an
antenna, radiating or receiving interference.

A "ground system" for a long wire or vertical antenna is really a
COUNTERPOISE for the antenna -- it provides the other half of the
circuit for the transmitter (or receiver) as a load. This is why
it is VERY important to bond the shield of the coax in a mobile
antenna system to the body of the car at the base of the antenna.
It isn't noise (although it might reduce noise), it's the other
half of the antenna!

The surface of the earth also serves as a reflector for the radio
waves radiated by the antenna. That ground system will work better
(be more efficient, have less IR loss) if it is has low impedance
at the frequency where it is used. High moisture content results
in very low resitivity and better reflectivity in the soil. It is
the combination of the reflection(s) with the direct wave from the
antenna that determine the vertical directivity of the antenna
system. These two mechanisms are the significance of RF ground.

Jim Brown K9YC
http://audiosystemsgroup.com


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