OBSERVATIONS    GM1SXX             29 Sept 2009

Half a dipole is better than none!

The coaxial trap described in the last of my 'Observations' has a practical purpose. It can be used in a W3DZZ type aerial... or even a half of the same!.

If like me, you can't swing a cat in the back garden, you may still be able to fit in HALF of a W3DZZ dipole aerial set up as an Inverted L to save space.

This aerial is fed at the far end, rather than at the house. It's essentially half of a W3DZZ trapped dipole, bent into an upside-down letter L, to save space.  So in reality it's an inverted-L trapped monopole fed against ground.  These can give good results on HF from a postcard sized garden.  On the higher bands, an AMU (otherwise wrongly called an ATU!)  is likely to be needed.

The concept is simple and the only thing that's important is to use a non-conductive  support at the end of the garden... a wood or fibreglass mast ideally. If your garden is 30 feet long or more, this will certainly fit, since the horizontal run will be around 30 odd feet.  Decent heavy stranded electrical wire can be used for the radiating element and a small plastic box at ground level allows the connection of the ground stake and radiator to the co-ax.  You can adjust the vertical and horizontal runs on the 33 foot section as required to fit the space available, so long as the overall length is not altered.  Like any monopole, a better ground results in better performance.  The vertical section should be kept as far as you can manage from metal objects that can de-tune it.  A varnished wooden mast can be used, or if you are rich, a fibreglass telescopic mast could be used instead.  

73 Al.

GM1SXX