[Antennas] Buried ladder line?

[W6jod@aol.com]

Amazing what a small amount of checking will provide!

I'm away from my home QTH but remembered I picked up a copy of the 1976 ARRL 
Handbook at a library used book sale a week ago.  Sure enough, in the section 
on transmission lines, there is a formula to calculate the impedance of an air 
insulated coaxial line.

Zo = 138 log b/a

Zo is the characteristic impedance of the line
where b is the inner diameter of the outer conductor 
and a is the outer diameter of the inner conductor
(diameters to be in the same units)
#16 gauge copper wire = .05082"

I then remembered the calculator built into Windows and found that my idea 
was not that great!

#16 wire with 1" copper pipe ~178.5 Ohms - Times 2X ~ 357 Ohms

#16 wire with 1.5" copper pipe ~203 Ohms - Times 2X ~ 406 Ohms

#16 wire with 2" copper pipe ~ 220 Ohms - Times 2X ~ 440 Ohms

The idea of threading a balanced line inside a 6" ABS or PVC conduit would be 
a fun test.  Go for it!

73,

Norm Hall, W6JOD


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