I worked at WPEN in Philadelphia as an engineer in the 1960s while I
was in high school. Their three-tower AM array was built in the 1930s
and all towers were fed with 4-wire open-wire line. The feedline used
diagonal pairs in parallel. I have some photos of the line if anyone
is interested.
I can't remember how the balanced line was coupled to the tower, but
my best guess is that it was a link-coupled winding. There were other
LC components to match the line to the tower impedance.
This was a directional (at night) array, so any feedline radiation
would have caused pattern distortion, so I'm pretty sure the feedline
had minimal radiation.
That site is still in use, although the self-supporting Blaw-Knox
towers were replaced with guyed towers about 30 years ago, and the
array is now fed with heliax.
Doug K3KW
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