Some years ago, John Belrose VE2CV published an article in QST about
off-center fed antennas, based on a combination of modeling and
building. While they look attractive on a simulation program (where the
feedline wasn't also modeled), he found that in practice it was very
hard to keep the feedline common mode current down to a low value. The
consequence of common mode current is that the feedline becomes part of
the antenna, and that makes it very difficult to duplicate or to realize
the idealized performance you might expect if you hadn't taken feedline
radiation into account. Multiple current baluns should be able to reduce
the common mode current to a reasonable value, but they'd have to be
used unless you want a lot of feedline radiation and performance that's
difficult to predict.

Roy Lewallen, W7EL

Buck wrote:
On Wed, 20 Apr 2005 23:21:29 -0500, (Richard
Harrison) wrote:


Cecil, W5DXP wrote:
"There would be three current maximum points on a 3/2WL wire."

Yes, and I believe they occur 1/4-weave back from the open-circuit ends
of the antenna and at the very center of the antenna.

Best regards, Richard Harrison, KB5WZI


Thanks, That's what I was looking for. so I can use the antenna with
1/4 - 3/4 or center loaded.

Would the off-center setting create another resonant frequency for the
antenna?

Assuming the antenna were cut for 1/2 wave at 7 MHz, it would operate
on 21 MHz, but if off-center fed, would it also resonate on 20 MHz
with the 1/4 wave element?

Thanks.