To build this antenna you need a lot that is at least 100 feet in any direction. The antenna covers all bands 80-10 meters + 30, 17, 12 meter bands.

This antenna works as a full wave loop on 80 meters and also works as a two-wavelength open loop or bi-square on the 40 meter band.
The gain is around 4 DBd on 40 meters, but it will seem much higher due to the very low angle, radiation pattern. Any antenna tuned for 80 meters should also work on 20 and 10 meters as well. If an antenna works on 40 it should work on 15 as well. A tuner will probably be needed for 10, 18 and 24 MHz band operations.

The loop is an inverted vertical triangle with the base along the top and what would be the apex hanging down. Or it could be erected horizontally if needed. The feed point at the bottom uses a 3:1 or 4:1 balun and is then fed with any needed length of 50 ohm coax. The top center is broken with an insulator and has a 29 feet 10 inch length of 450 ohm ladder line connected across the insulator.
IMPORTANT - The 450 ohm ladder line is shorted across at the bottom end.

Here is how to calculate the loop size.
Dimensions - One wavelength at say 7.25 MHz = 1005/7.25 = 138.62 or 138 feet 7.5 inches. If this length is doubled and used on 80 meters as a loop then freq (for a loop) = 1005/(2 x 138.62) = 3.625 MHz. The 1/4 wave stub = 246 multiplied by (velocity factor of your type of ladder line) /7.25 = about 32 feet.

Ladder line velocity factors vary by brand, type, insulation, etc. The best method is to use a grid dip oscillator or antenna analyzer to measure the resonant frequency of the 1/4 wave matching stub during construction, rather than by just using the mathematical formula to determine the length.

The perimeter of the 80 meter loop for 3.625 MHz = 277.24 - (2 x 29’ 10”)[2 x 29.86 feet = the length of both sides of the wire in the ladder line] = 217.52 ft. Let’s call it 217.5 feet. If the top horizontal span is made 99.5 feet overall and the legs 59 feet each then the balun will hang about 30.5 ft below the top center insulator. The 29’ 10” ladder line can have its bottom - shorted end  - tied to the top of the balun with a short length of fishing line, weed eater line, string, or cord etc. On 40 meters the ladder line stub automatically acts as a switch and opens the connection across the insulator so the antenna works as two one-wavelength loops fed in phase. This antenna is a high performance, full size, full wave, 80 meter loop antenna.

On 40 meters, it is a two-wavelength open loop or bi-square. The stub in the top leg of the antenna opens the loop when operating on 40m and selected other bands. This improves the antennas radiation pattern. Its gain is around 4DBd, but it will seem a lot higher due to its excellent, low angle, radiation pattern. The 50 Ohm coax from the balun to transmatch is not critical but recommended to be 1/2 wavelength. (99 feet of RG-8X). This antenna could also be configured as a 54’ 4.5” square on a horizontal plane. The 217.5 ft loop can be pulled into almost any shape but the bigger the “aperture” enclosed area the better it will work. 

Radio-Works also makes this antenna now.  Return to WC4R home page.