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[TowerTalk] rf choke or balun?

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Subject: [TowerTalk] rf choke or balun?
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Date: Tue Jun 3 06:19:44 2003

>> What am I missing here--I don't understand the difference between a "balun"
>>  (at least a 1:1 balun) and a "choke."  
>>  Aren't they in fact the very same thing?  If they each were in a "black
>>  box," would they not both appear the same? 

The way I understand it,

a voltage balun is a "REAL" transformer with TWO MAGNETICALLY COUPLED coils 
wound on a single core.

The problem here is that many things can go wrong during the construction 
of the balun (e.g. frequency dependancy, self resonances, etc...).
These effects affect the COUPLING process,
so there are many circumstances under which quite non-than-optimum coupling
can occur, resulting in a bad or lossy balun, meaning the energy flow from one
side of the balun to the other side is much less than optimum

An rf choke is a device where both antenna wires are physically connected
to the
coax, one wire to the inner connector and the other one to the outer shield.
The only thing that is done is putting a severe "choking action" on the
outer shield 
of the coax cable. This "choking action" can be achieved by several ways, e.g.
sliding ferrite pearls over the coax shield or coiling up the coax or...

This method (rf choke) is much less error prone than the 2 magnetically
coupled coils.
Also the core of a voltage balun must be capable of transferring the whole
power from
one side to the other.
The choking material (e.g. ferrite pearls) must only be capable of blocking
the current 
on the outer shield.

Talking about a "black box",
yes, if you have an ideal voltage balun and an ideal rf choke inside each
black box,
you will not be able to measure the difference from the outside.

Is that correct?

73 Con DF4SA

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