Topband: Using Video Baluns on 160.

[Rick Karlquist]

Herb Schoenbohm wrote:

> Recently I purchased some video baluns to use for an FM station to
> remove hum from cables feeding a composite audio single from the

I did some design work on video baluns a few years ago.  They consist
of a large number of turns of twisted pair on an ungapped pot core.
Old fashioned analog video is best sent with DC coupling.  If that
cannot be done, AC coupling can be used if the low frequency response
extends to something like 30 Hz.  It is possible to add DC restoration
to take care of the missing DC.

Having said that, there is no such requirement for topband work.
You can get even better isolation by using a conventional flux
coupled transformer instead of a common mode choke (referred to
commonly as a "balun").  I have been using Mini Circuits T1-6
and similar transformers for years in this manner for receiving
antennas.  I have also wound my own on binocular cores.  You
wind them the same as "baluns" but connect the wires differently.
When you do this, the finite impedance of the ferrite is applied
in shunt with the signals, and has no effect on the isolation.
It is not in shunt from input to output as with the balun
configuration.

Rick N6RK