This might be of general interest to people with long feedlines.
I'm installing a very tall tower for an expanded 160 system 1400 feet back
from my shack. I needed a low-loss feeder to get RF back there, so I
decided to pull an open wire line made from number 8 copper wire spaced
just under three inches. That makes it about 450 ohms.
My matching transformers using 61 Ferrite Material (9:1 balanced to
balanced) and baluns (1:1 choke baluns) have a single unit loss of .17 dB
at 15 MHz, immeasurable loss at 2.5 MHz. They are designed to handle a 10:1
VSWR at 2 kilowatts CCS. Applying 2000 watts CCS for 1/2 hour, they remain
stone cold.
The total measured loss of this system really shocked me. I knew open wire
line was good, but not this good. Matched power loss on 2.5 MHz was 0.33
dB, including transformers! 15 MHz loss was only 1.3 dB. That means
feedline loss was about 0.3 dB on 2.5 MHz and just under 1 dB at 15 MHz.
Apparently there is a lot to be said for using true open wire line. Loss in
1400 feet of line is about the same as loss in 100 feet of RG-213/U. Not
only that, I can run my tower light power through the same wires.
73 Tom
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