[TowerTalk] common mode chokes, baluns and multiband, doublets

[Rob Atkinson]

Sadly, it seems little is known about how to handle balanced line
outside the vintage radio community.  QST doesn't help.  The Doctor Is
In column does anything and everything it seems, to get hams to use
poorly made "window line" with items such as baluns and unbalanced
matching networks.

The load on a balanced line does not have to be perfectly balanced,
but it does have to be close, for the system to work well.  But the
idea that this is difficult is misguided.  It's not that hard to
achieve an almost balanced system.  Firstly you have to be able to
measure the currents in the line on each side in the same place.  A
pair of thermocouple RF current meters can perform this.   Feeding a
dipole in the center that is high up with equal supports will work.
Sometimes another antenna near one side of the dipole will unbalance
it but if you float that antenna, disconnected from the shack or
ground, that is often enough to solve the problem.  This is called
experimentation, and it is fun if you desire to advance beyond plug
and play radio.

>Some of the "things" also implement impedance transformation, but impedance transformers don't necessarily perform the balun "function," adding to the general confusion.


The EF Johnson Matchboxes are "baluns" and they transform impedance.
It's an all in one deal, but for some reason, the contemporary amateur
radio community is ignorant or somehow distrustful of link coupled
matching networks.


73

Rob
K5UJ