4m Slim Jim

This 4m Slim Jim is cheap and easy to build and offers good performance due to it's low angle of radiation. An SWR of 1:1 is obtainable across the 4m FM band with simple adjustment. The photograph and PDF diagram show the construction, however a brief description is given here. The spreaders are made from plastic knitting needles; two small holes are drilled about 10mm in from each end of the spreader to accommodate the aerial wire. Suitable sized holes are then drilled in the fishing pole to mount the spreaders. The spreaders are then glued in position using a two part epoxy. The telescopic fishing pole sections are also glued to each other using epoxy. Once the glue is set the antenna wire is then threaded through the spreaders according to the diagram. RG-58 is connected to the matching section but not soldered yet, just wrap the braid and inner around the aerial wire. For the aerial wire I used annealed bare single core copper wire.

Setting up

Raise the antenna at least 3m above ground and clear of any objects (walls etc), apply a few Watts of RF and adjust the feed point to give a 1:1 SWR (slide the RG58 up and down the matching section). When the correct feed point has been found, solder the feeder connections. I dabbed some yacht varnish over the connections and the first couple of inches of the coax to stop water ingress down the feeder.Mount the aerial as high as possible; due to the construction materials the wind resistance is low so it should survive the worst of any storms.

Barry Zarucki M0DGQ