SARTS Talk Apr 2011: Design and Matching of a Rubber Ducky Alternative by Jeff 9V1AS

This is a light-hearted talk I gave to the club on meeting night in Apr 2011.

Meeting nights fall on the last Thursday of each month (except June and Dec). I always look forward to exchanging tales, eyeballing, drinking beer etc with my ham pals – very happy time !

The motivation was to build a whip antenna which would outdo the one that came with my Icom V8 handie. The starting material was a telescopic antenna of doubtful pedigree which I bought from my favourite gizmo shop on the 3rd floor of Peoples park Complex, for $2.00. The 5 to 50pF tunable “barrel” cap was had for 30 cents at the same shop.

My AIM 4170C was used extensively for this exercise.

Scanning the web before I started on this endeavour, I noted that there were countless articles on matching circuits for HF antennae, but very few on matching circuits for VHF and UHF whips. I realised that a knowledge of the Smith Chart and the methods of traversing the chart using L and C elements would be invaluable.

My favourite  Smith Chart Program is by Prof Fritz Dellsperger. The demo version is sufficient for this application.

On opening up the base of the telescopic, I found that the telescopic section was not electrically connected to the pin of the BNC, hence my calling it a “Whip to Nowhere”.

My trusty old HP 4342A Q Meter proved invaluable in measuring the coils I made in the nH range.

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Thanks for reading!

73

Jeff 9V1As

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