You don't always need to precisely cut your antenna if you have a part of it coiled up and switched. Here I take 4.6m of thin insulated wire and connected it to five shorter pieces (about 10cm long) wired across a rotary switch. This allows its length to be varied. The advantage of this is that you can cover about a 10% frequency range rather than the 3% that a fixed length antenna covers. This experiment was with a 1/4 wavelength vertical on 14 MHz but if you want to do it for 28 MHz I would suggest using about 2.3m for the vertical element and pieces of 5cm long across the contacts of the rotary switch.

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