[TowerTalk] Re: coax as balanced line

[Bob Duckworth]

What makes things work?
VooDoo!
What keeps them from working?
Bugs!
What makes them break?
Gremlins!
Who is the Chief Gremlin?
Murphy!

Assumptions:

Matched line (no radiation)
Pysics is a constant :-)
We are talking about a parallel transmission
line with the individual conductors shielded
NOT two pieces of coax fed via a splitter with
a combiner at the other end.

Given the above the transmission line loss 
will come from two things.

Ohmic loss
Dielectric loss

1)Ohmic loss.

The ohmic loss depends on the material.
The frequency determines skin depth but it doesn't
change. So Ohmic loss for parallel wires is half
of that of one wire. Loss will be less than the coax.

2)Dielectric loss.

In a piece of coax E field (dielectric loss part) lives 
in the dielectric pretty much entirely.

In two pieces of Coax (a balanced line with a shield
for each conductor)  the field lives between the two 
center conductors. In other words, there is a portion 
of the field living in the air which has extremely low 
dielectric loss. Loss will be less than the coax.

Convinced parallel line has lower loss?
Want to know how much lower?
Do the math.
Comparing a sheet to a solid cylinder around the wires 
should be give a fair approx of the difference.

-bob
wb4mnf
(I am not an engineer!, Don't you dare call me an engineer!)


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