Currently, the operating position is located in a spare area of the house.  For various reasons it was not practical to bring a long wire and associated earth system into that part of the house.  I had previously installed an underground co-axial feed between the house and the shed so this was utilised to connect the transceiver to the remote, manually tuned coupler.  This set up worked well but whenever I wanted to change frequency or band I had to take a walk up to the shed and plug the antenna analyser into the coupler to make the necessary adjustments then reconnect the co-ax and head back to the house.  This can be quite time consuming so I decided to look at other options. Over a period I obtained the necessary mechanical parts needed to build a remotely controlled unit.   

This version of the antenna coupler is configured as a differential 'T' pass.  The roller inductor and capacitor are coupled together via a belt drive.  The ratio is 1:1.  With a 128' end fed wire and a suitable earth system I can achieve a good match on all ham bands of interest to me; in this case 160 through 20 metres.  For every complete turn of the inductor the capacitor goes from min to max capacitance.  I intend to change the gearing so this occurs for every half turn of the roller inductor.  This should give a bit more 'fine tuning' accuracy.

I have yet to complete the visual tuning indicator circuit so I can remotely monitor the tuning process.  I intend to use a 10 turn potentiometer and a 3:1 geared drive coupled to the inductor's shaft which will be sufficient for the 30 turns of the inductor.  Micro-switches at each end of the inductor limit the travel of the roller.

The roller inductor was sourced from eBay in the United States and the capacitors were purchased from the VKHAM web site in Australia.  I believe they were originally used in a Codan H.F. base station.  Eventually the completed coupler will be mounted in a weatherproof enclosure and positioned at a suitable location to allow a multi-band earth radial system.

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This page last updated on Thursday, 15 November 2007