GW4RWR - Replacing the Tonna Driven Element

 


I read some adverse remarks about the 9ele portable Tonna being too flimsy. But it's a lightweight antenna, and weight matters on a long walk. Furthermore the elements are pretty flexible, they have bent when stiffer elements would have snapped. Windloading is also minimal. I've operated in a contest with this antenna, when the wind was actually so strong that I was blown over.

In 2010 I caught and snapped the driven element on heather as I walked up hill for a contest. I pared back the plastic, and bolted a replacement tube to the remaining metal, and it was used in this 'splinted form' for another two years.

 

Time took its toll. The plastic cracked and was strengthened with filler; the threaded mounting hole lost its thread, it had to be tape wrapped to the boom. The fractured element drooped. It was all a mess and it's amazing that it worked at all. Apart from this cracked plastic, the other design fault is that the single mounting bolt screws into a shallow plastic thread. It can break very easily.

Having pared back all the plastic, I found that the T-match was riveted in position. Rivets were drilled out, and the T-match bolted (M3) to a replacment element, made of 3/8" 18 SWG tube. The plastic housing is kept in position by two bolts; this is much better than the original design. A Tonna replacement driven element would have cost 40.95 - more than the complete antenna cost in 1983!

The RG-58 cable shown was replaced by with Pope H-100. I won the RSGB 2013 Backpackers Championship with this antenna, so it must be working.