The 80m/40m antenna is my own design. The thicker a dipole wire is (relative to its length), the wider the bandwidth. You can get almost the same effect as a thick wire by using a number of wires in what they call a cage. When I was in Framingham, I reduced that cage to only 3 wires in a triangle with the wires about 18 inches apart. At that time, I used coaxial wire traps (the coax provided both inductance and capacitance) to make the 80m/40m combination. But the traps were too sharp and it did not quite cover the entire bands. There was also loss in the traps.
So
I experimented with running
both 80 and 40 meter antennas from the center fed position. A choke balun is
made by winding RG-58 wire around a T2 Toroid to minimize the RF in the shack.
The goal was to provide better than 3:1 SWR over the entire 80m (and 75m) and 40 m bands. That is the limit of the built in antenna tuner in the Yaesu FT-450 transceiver.
The 80m/75m antenna and the 40m antenna are now down to a two wire "cage" each. The wires are spaced 5 inches apart. So you see 4 wires for the 40m length (about 65 feet end to end) and the top 2 of those wires extend for the 80 m length (about 130 feet end to end). The spacers were made out of 1/2 inch PVC conduit. (Note: 1/2 inch conduit has an outside diameter of 3/4 inch) The 6 spacers (3 on each side) closest to the center are 15 1/2 inch long. The remaining 4 spacers (2 on each side) are 5 1/2 inch long.
Each end of the inverted "V" antenna is tied to 3/8" nylon line through an insulator which is simply a 3 inch piece of the same conduit used for the spacers above. The lines run through a pulleys about 10 feet above the ground to a winch (similar to the one on the mast) on each end. The winch is used to provide slack in the antenna when ice weighs down the line. Slack is also provided before lowering the antenna through the pulley on the mast.
There was some interaction between
the two antennas, so the final step involved trial and error trimming of both
antennas to make them cover the desired bands. I ended up with 65' 11" for
the 40 meter antenna and 120' 1" for the 80/75 meter antenna. But you can
expect that to vary with soil conditions, height above ground, etc.
The wire and line ends were tied
with two half-hitch knots.
Inverted "V" Antenna Calculations
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