80 Mx Multiband Horizontal Loop Antenna
This multiband antenna covers the 80, 40, 30, 20, 17, 15, 12, 10 and 6 Mx Amateur bands. Multiband operation is achieved by use of 300 ohm balanced line fed to an antenna tuner. This loop antenna needs to be run in the horizontal plane. ie. parallel to the ground. The formula used to determine fundamental frequency wire length is :- Length (feet) = 1005 / Frequency (Mhz). I operate mainly CW, so I cut the wire length, for the 80 Mx band, to 88 metres (287 feet). If you operate SSB, the length of the wire will need to be shorter, in accordance with the above formula. I used high tensile fencing wire in the shape of a square supported by four trees. The winds here can be ferocious so strong wire is needed even though radiation efficiency may be compromised by using fencing wire. Since our HF bands are harmonically related, this length of wire covers all HF bands from 80 mx up to 10 mx, including the WARC bands. If the wire is cut for the 40 metre band, about 44 metres of wire or slightly less, the antenna can also be used on all the higher HF bands. Of course, a perfect square of wire is far from achievable here. A circle is theoretically ideal but even a triangle of wire will work. The feedpoint of the antenna can be placed any where but I positioned it about two feet from the corner. The diagram below gives you some idea of the layout.
This image shows one of the trees to which the wire is attached.
The trees at this location are not very high so the average height of the antenna is only about 20 feet or so.
The feedpoint can be seen on the left. I used 15 metres of 300 ohm ladder line
which can be purchased in various lengths from DXEngineering.
A perspex block and splicing tape reduce the strain on the feedline at the feed point.
Rubber splicing tape can also be purchased from DXEngineering.
One 'corner' of the antenna.
The operating position located in an old caravan which is solar powered. The tuner can be seen on the
left. The radio is the Yaesu FT-450.
The Tuner - MFJ-969.
Even at a low height, this antenna performs very well. Surprisingly so. One of its attributes is the low noise level of the antenna. Another is that it has many radiation lobes and therefore works well in several directions. It costs little to build. It's straight forward to construct and fairly easy to erect, although in my case I had a sore shoulder after throwing the lines up into the trees. This multiband horizontal loop may be the antenna you are looking for.
Also, Ed, VK2JI has an interesting article about his 40 Mx Loop - click here.