Albert H wrote:A fairly quick and easy way to make a frequency-adjustable aerial is to make (say) a ⅝-wave vertical, with groundplanes that are (roughly) ¼-wave long at 88 MHz. The radiating element needs to be made out of two pipes, with one that fits inside the other. The outer pipe needs to be ⅝-wave at 108MHz, and then you progressively extend the radiator as you go down the band. You'll need a simple C - L matching circuit at the base of the aerial to get a good match to 50Ω, and an SWR bridge to confirm the calibration of the aerial.
The other - possibly easier - option is to make a set of the cheap Slim-Jim that are described in
http://radio.xtreamlab.net/omni-aerial.html. If you make them centred on 88, 91, 94, 97, 100, 103, 106MHz, you'll get a reasonable match at any frequency on the band, since the wire Slim Jim is close to 3MHz wide if you use fat wire. I made mine out of cut-apart 10mm Twin-and-Earth cable, keeping the uninsulated earth for use in coils in PAs and aerial matchers.
At the moment I dipole antenna works pretty well, but will study these antennas, thanks !!!
