Ham Radio

Tuesday, November 05, 2019
80m Dipole - SWR Adjustments

The home made wire dipole that I recently installed was showing an SWR reading of 1:1 at 3.600 MHz. Higher up the band at around 3.795 MHz I was getting a reading of 2:5 which meant I needed my ATU.

After the third time of lowering each end and cutting off 6inch lengths from both sides I got a much more useful range of SWR readings.

The last Adjustments now read 1:1 at 3.700 MHz and 1:3 SWR on 3.799 MHz which is pretty much spot on.

The original dipole legs were cut on the generous side in the first place which meant cutting/shortening each side equally. I did it this way to gain optimal performance on the frequencies I most want to operate on without the requirement of an ATU. It can be tricky measuring the exact length of wire needed as lots of factors can alter the SWR such as antenna height, angle, length of feedline. Location and objects near by etc. By making your dipole oversize it's easy to adjust each end to get the perfect SWR and also a good excuse to mess about outside h.i

If you want to make one for yourself, I used 2.5mm copper multi strand wire. covered in pvc insulation (brown) obtainable from any electrical fittings store. A dipole centre, two end insulators and a short length of light weight 50ohm coax. Each wire leg was cut at total length of 66 feet. After Adjustments the antenna was near to 130 ft total
 Each leg ended up approximately 65ft in length.
posted by MØYKS - Simon @ 11:41 pm  
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