The 2015-2016 Antenna Farm - G7SYW's amateur radio bits & bobs...

The 2015-2016 Antenna Farm

| Posted in Antennas

It wasn’t so much a farm – more like a window box!

HF homebrew multiple dipoles

My last QTH had a tiny postage stamp for a garden, less than 30 feet x 30 feet. Additionally, I also had the problem of overhead power cables that ran parallel with, and about 18 inches away from the back fence, thus installing any kind of HF antenna required a bit of homebrew ingenuity, this is where the ability to experiment with antennas came into play – enter the dipole!

Due to not having any nice tall trees nearby, nor being able to erect a tower or attaching any kind of pole or mast to the building I had to improvise.
I constructed a bracket with a pulley and attached it to the top of the soil pipe at the back of the house. Nylon rope through the pulley to allowed me to raise and lower the dipole as required.
Original fan dipoles

This also formed the support for the centre feedpoint of the dipole. Although the soil pipe was made from
cast iron it didn’t affect the SWR as the antennas and coax feeder moved around slightly in the wind.

In the true spirit of amateur radio I began to wonder if I could nest further dipoles for other bands, the only restriction being the space available.

I added wires for 40M (7MHz) again in a similar sloping V shape but with the ends bent around to follow the line of the fence as this was the only way to fit them into the garden.
Fence supporting dipoles

Because the ends of the 40M dipole are further away from the feedpoint than the ends of the 20M
dipole this forms an almost horizontal V formation.

The added advantage of the 40M dipoles is that they are also resonant on the third harmonic, which just happens to be the 15M band (21MHz).

I also added wires to cover the 10m (28MHz) band.
With the aid of the radios built in antenna tuner I had access to all the HF bands from 80M to 10M.
However, due to the rather shortened electrical length at 80M the dipoles are very inefficient, but considering the level of RF noise on frequencies below 7Mhz (40m) at my old QTH it was not worth even trying to use the higher bands.

In summary, it was a far from ideal solution, but at least I was back on the air!
A good article for constructing a multiband fan dipole can be found here