There is an exponential extinction coefficient that governs penetration
of RF currents below the surface of conductors. Lower freq means
greater depth of penetration or in other words how thick is the skin of
the skin effect? The lower the freq the greater the depth of
penetration. In the limit as freq goes to zero (DC) the entire wire
conducts.
If you have access to a micro ohm meter or miliohm meter if you use a L
O O N G piece of wire you can compare the DC resistance of your
candidate antenna material to the published specs for steel or copper of
that gauge.
Making DC measurements you can treat the wire as two resistors in
parallel, one is the copper resister and the other is the steel
resister. With a measurement of your wire's resistance per unit length
you will be able to assign a cross sectional area to the copper and to
the steel. A little arithmetic later... and you should be able to
calculate the thickness of the copper cladding.
Properly instrumented you would be able to measure the change of
resistance per unit length as it varies with freq and get the same
answer more easily.
Patrick NJ5G
On 8/8/2014 3:54 PM, Gary Schafer wrote:
I have lots of old copper clad telephone wire that I want to use for radials
and antenna wire. This is the stuff that is bare and went from pole to pole
for old telephone lines. It is not the insulated drop wire.
When you cut it, it looks like copper all the way thru but it will attract a
magnet.
I want to use this stuff on the low bands (160, 80, and 40).
Is there a way to measure/determine how thick the copper layer is?
Measure the resistance, wind a small coil and measure Q?
Thanks,
Gary K4FMX
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