| So you obtained a great commercial 8 bay exposed dipole array antenna for your amateur repeater. You drilled the holes, mounted everything and oops - The S.W.R. is 3:1 or more. Definitely not suitable for a use with a repeater duplexer or the poor repeater amplifier. It will be nothing but trouble. Don't throw it away. There is a solution, it's easy and does not damage the antenna. This method is meant to tune an exposed dipole array originally designed for frequencies above the desired frequency only. The fix, simply install an air capacitor on each dipole. This will lower the resonant frequency of the antenna. The capacitors are made from aluminum strips about an inch long and 3/8 inch wide. Make each strip as identical as possible. Drill a hole just large enough to be bolted to the array where the dipole gap is. Position the strip so it is about 1/8 of inch above the adjacent side. Adjust the gap for each capacitor to be the same. You may have to adjust the gap or make the strips larger or smaller for your particular antenna. This works extremely well on Decibal Products 8 bay UHF arrays. The SWR went from 3.5:1 down to 1:1 and performance is excellent. |