Nick, N6RK, asked why are 4 wire transmission lines used?
The article does answer some of the questions; the subject is too
lengthy for my article, and of course not here. In GENERAL for 4-wire lines:
1. Considerable lower characteristic impedances; calculate 200 ohms
with a two wire line.
2. In commercial use, the lower impedance makes for less susceptibility
to irregularities introduced by insulation ans switching arrangements.
3. In high power capacity for the same amount of copper, its
attenuation can be less than two wire feeders. But transmitting loss
can be lower in a two wire line with large copper conductors.
4. Cross connected 4-wire lines (vs side connected)have a smaller
external field and have lower pickup when receiving. Riverhead said a
4-wire line properly handled can outperform coaxial lines in terms of
reduction of unwanted pickup. But cross connection does have a slightly
higher loss.
5. With #14 wire spaced 1 9/32 inches, an impedance of 242 ohms is
obtained when side connected, and 200 ohms when cross connected.
SPECIFICALLY. Twenty five years ago, I felt it was "cleaner" to use a
low impedance line, and I wanted to "play" around with four wire lines.
Jerry, AI6L, I said "The side connected four line was used in this
project because I thought the transmitting characteristics were of
greater importance than the receiving ones." But somewhere along the
time line of life, I switched to cross connection to get the 200 ohm
characteristic impedance.
Over the quarter century of use, the wires have stretched, and with 70
feet spacing, and birds sitting on the wires, and from high winds, they
have gotten tangled at times. I have a 12 foot piece of base board that
I insert between the wires and separate them. Once I even had to
tighten the turn buckles at the end of the run, which fixed the problem
for another 10 years. Using open wire feeders 2,4, or more, sure beats
buying coax to where you really want your antenna to be.
I will reply to you others directly, and yes, I'll send you some
insulators for your use or museum purposes.
Vy 73 Henry
Henry G. Elwell, Jr. - N4UH
Good, better, best...never let it rest until the good is better and the
better best.
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