4m J-pole        
The 4m J pole (Slim Jim) design may be found on here on The Four Metre Website. As Andy G0BEQ points out in his article, some people (including Ian GW8OGI and myself) have found that, using the measurements quoted, the aerial was 'off resonance' by several MHz resulting in an unacceptable SWR. Ian GW8OGI experimented with an analyser and wire cutters, and came up with some alternative dimensions that worked for him using black 'semi windowed' 300 ohm ribbon. I have built two units to Ian's dimensions, and both worked fine with an SWR of just over 1.2:1.The 'modified' dimensions are shown in the diagram alongside. Image
On the versions that I have built, the top (and bottom) of the aerial has a small length of 'heat shrink' material slipped on before the wire ends are soldered together. The heat shrink is then pushed back over the joint and given the 'heat treatment'.The top section uses two tie clips to enable it to be slipped onto the top of the 'fishing pole' used in summit activations.(see the picture below).

On these versions, I used RG-174 cable and simply 'taped' over the joint (see below left). I sealed the 'gap' in the antenna with a bit of heat shrink (red in the photo) and 'taped' it to the other side.

I also use a couple of reuseable tie wraps (obtainable here) to hold the antenna in the middle and and at the bottom which stops it from flapping about too much on the fishing pole, otherwise in windy conditions listeners can hear an effect remarkably similar to mobile 'flutter'.

The whole antenna is very light weight and can be carefully coiled for easy transportation on summit activations and both Ian and myself have had great success with this design. Forget your 'rubber ducks' and 'whips', this antenna will beat them hands down.

It would also make a good base antenna too. Tape one to that retired fishing pole, or put it inside some plastic electrical conduit.

(My thanks to Andy G0BEQ for the original concept, & Ian GW8OGI for the modified dimensions)

Mike G4BLH

It is indeed a very good antenna to accompany the e.g. Wouxun KG699E handheld. I found the joints at the feedpoint are not too robust. I fitted a chocolate box terminal block and hot-glued it and the connected wires to a 4" strip of 6mm ply. I have cable ties bridging the other weak points and acting as strain relief for the dangling coax choke. I hope the phrase "no 4m - the antenna is broken" is consigned to history.

David 2E0DAI

Created by G4CPS. Last Modification: Wednesday 27 of February, 2013 09:56:49 GMT by G4CPS.