When is a balanced feedline balanced?

When is a balanced feedline balanced?

Post by John, N9J » Tue, 13 Nov 2007 22:18:22

When a wire flattop is fed with parallel line, what are the affects on the
system when the feedline is not perpendicular to the flattop? It would seem
to me that the system, consisting of flattop and feedline is no longer
balanced, and the feedline will radiate on transmit and pickup local noise
on receive.

Any comments will be appreciated.

John, N9JG

 
 
 

When is a balanced feedline balanced?

Post by Cecil Moor » Tue, 13 Nov 2007 22:57:40



> When a wire flattop is fed with parallel line, what are the affects on the
> system when the feedline is not perpendicular to the flattop? It would seem
> to me that the system, consisting of flattop and feedline is no longer
> balanced, and the feedline will radiate on transmit and pickup local noise
> on receive.

Essentially correct but common-mode chokes and/or
link coupling can help. And it's not just a parallel
line problem. Coax that is not perpendicular to
the flattop suffers essentially the same problem.
--
73, Cecil  http://www.w5dxp.com
 
 
 

When is a balanced feedline balanced?

Post by Roy Lewalle » Wed, 14 Nov 2007 07:53:11


> When a wire flattop is fed with parallel line, what are the affects on the
> system when the feedline is not perpendicular to the flattop? It would seem
> to me that the system, consisting of flattop and feedline is no longer
> balanced, and the feedline will radiate on transmit and pickup local noise
> on receive.

That's correct. Common mode (unbalanced) current is induced into the
feedline by the unequal radiation from the two halves of the antenna.
This also occurs with an off-center fed antenna even if the feedline is
perpendicular, and with coax feedline.

Roy Lewallen, W7EL