[Amps] RF in the Audio
w9ac at arrl.net
Tue Sep 27 04:45:57 PDT 2011
> On 9/26/2011 6:58 AM, Paul Christensen wrote:
>> Even if the line is truly balanced, that balance would exist in
>> transmission, but not necessarily in receive.
> It isn't as simple as that. The ANTENNA is also part of the balance
> equation, and if the antenna is unbalanced, it will cause imbalance in
> the line...
Good points Jim. However, if the line was truly balanced for the entire
distance of the open-line feeder, then the antenna portion, and its
influence, is already taken into consideration. To your point (I think),
this condition never exists with an HF dipole except in theory as uneven
placement (even if slight) of the radiator to the line as well as mutual
coupling effects to other objects will have some influence on line balance.
The reason I said "for the entire distance" of the open line feeder is that
line current may appear equal when measured at the bottom of the feeder, but
coupling from one conductor may cause a third current path mid-way on the
feeder and cause an imbalance into the radiator. That's a similar condition
as the "third current path" on the outside conductor of a coaxial line, but
is mitigated with a CM choke at the radiator feedpoint.
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