Last year I installed a "Jamac" antenna in NVIS configuration for 40m.
Just threw up two 140 dipoles, spaced 70ft apart and feed wtih 600ohm
line. The elements are 15ft above earth (sandy loam to a depth of about
During this monsoon season, or sorry, Spring I thought I'd check the
resonance of the full wave dipole elements. By formula the wires are
long but I've heard that the closer the wires get to earth the shorter
they appear relative to freq. I fully expected to have to trim a few
feet of wire off the 140 dipoles. To my surprise the dipoles were
resonant about 7.5Mhz, at least that is where the MFJ analyser showed
zero inductance. In fact the MFJ reading was zero inductance from about
7.5-8.0Mhz. Net-Net I ended up adding 6ft to the ends of the dipole, so
total lenght is now 152ft
The MFJ shows a dip and zero inductance at 7.200.
Does this all sound about right?