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

[Jim Brown]

On Thu, 18 May 2006 16:40:39 -0700, Ron D'Eau Claire wrote:

>you'll have no RF ground at all at the rig

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