Fw: [Boatanchors] 300 ohm twinlead?

[Glen Zook]

Or, you can make your own.

The formula for the nominal impedance of balanced line
with air dielectric (spreaders don't have much of an
effect) is

276(log(D/R))

log is base 10

D is the distance from center to center of the wires.

R is the radius of the wire used.

or use this formula if you are dealing with the
diameter of the wire

276(log(2D/d))

where d = diameter of the wire (which is given in all
of the older ARRL Handbooks for each "normal" gauge).

As an "aside", the question of what impedance railroad
tracks would have came up on QRZ.com a while back. 
Using the formula it turns out that they have an
impedance of between 270 ohms and about 300 ohms
depending on just what the rail is used for (how heavy
the rails are made).  Side tracks are lighter rail
than spurs, spurs are lighter than main lines.

There was a "blurb" in QST in the late 1950s about
amateurs in Hawai'i using chopsticks for spreaders. 
They were drilled, then boiled in parafin for
weatherproofing.

Glen, K9STH


--- Jim Wilhite <w5jo at brightok.net> wrote:

Another choice is Ladder Line made by Gary, W7FG. His
uses spreaders and wire like on the old type of line
and not completely encased in the plastic.

Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco


		
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