TopBand: Ground clarification

[W8JITom@aol.com]

In a message dated 96-09-12 10:55:53 EDT, you write:

>Certainly the comments about the choke balun (s) are clear, but what grounds
rods?  >Aren't we trying to isolate the feed line from ground at the antenna?

Not necessarily. We are trying to establish something "electrically firm" for
the antenna to "push or work against". On receiving, the MOST important
requirement is the low impedance electrical mass used as a "ground" must not
contribute or conduct any signal to the system. That requires a large low
impedance electrical mass that is either so well distributed that EM
radiation does not excite large voltages at the terminals, or a small
electrically symmetrical system totally independent of any conductors
carrying unwanted signals.

The last thing we need attached to the feedline or used as a "ground" are a
few non-symmetrical radials that act like antennas as well as "grounds". Of
course the best ground would be a very large radial system that approaches a
solid symmetrical plate extending a long distance. In the general case of a
receive only system, multiple ground rods avoiding non-symmetrical attachment
to long conductors is prefered, ESPECIALLY when the antenna is near other
conductors.

Feedline chokes are most effective when accompanied by ground rods that have
no low impedance paths that shunt the choke, and no "random wires" or ground
loops that might contribute unwanted signals. This also applies to receiving
antenna ground connections unless a large symmetrical ground system can be
installed.

73 Tom

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