I slapped together an 80m dipole using the L=468/F formula and find that it
resonates about 200 KHz lower than expected.
My target frequency was 3.775 MHz. That's 124 feet on my calculator.
I built it using some left-over solid copper 12 gauge plastic jacketed house
wire. I center feed it with 100' of RG-59/a coax. One end is up 60 feet, the
other end about 40 feet. Using my AEA HF Analyst, it dips at 3.585 MHz with a
VSWR of 1.6:1. This is a 5.3% difference in length from the formula.
I can easily trim the length to meet my design goal, but I am curious why
theory doesn't match reality a little closer. Does the plastic jacket affect
the length? I would expect the resonant point to drop somewhat if the antenna
was "dragging on the ground". Or is 50' of height not adequate?
Thanks for any insight!
73 de Bob - K0RC
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