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The picture above is the rebuilt Thunderbird with a nine element 2metre Tonna and a GP15 above it.

The Hygain TH3 mark 3 Thunderbird antenna refurbishment ( Start May 2005).

I decided to put this article together as I had been looking for some information regarding the refurbishment of a TH3 tribander especially the traps I could not find much but what I did find out regarding the traps was conflicting.

One site said do not try to disassemble the traps and another source from TowerTalk http://lists.contesting.com/archives/html/Towertalk/1998-12/msg00250.html said it was ok and gave a description of how he had taken the traps apart, although this did not work for me as described it did inspire me to have a go at stripping down the traps.

In April 2005 I bought a second hand TH3 mk3, the add said in need of TLC.When I collected the antenna all the aluminium tubing was ok but the fasteners, those which had been plated steel were rusted away and some on the boom to mast clamp bolts were totally solid from rust and aluminium oxide.

My main concern was the traps as I peered inside through the drain holes I could see that there was corrosion on the inductor and element tubing .

A picture is worth a thousand words, or so they say.



You will see from photo-1 and photo-2 a large amount of corrosion on the trap. I found it difficult to clean the wire in situ so I carefully unwound the trap and cleaned up the wire with scotchbrite. I also cleaned up the coil former and aluminium tubing before rewinding the trap.



photo-3 and photo-4 shows how well the aluminium trap cleaned up. ( I had first thought that I would have to replace this wire.)

I stripped down the traps I had checked the resonant frequency with a GDO calibrated against my FT1000MP MK5 field. On the 10 metre and 15 metre parasitic traps,10m = 26.5 Mhz and 15m = 19.1Mhz approx.I then check the resonant frequency on the rebuilt traps and to my surprise I could not detect and change in frequency or depth of dip. So was it worth all of that time and effort?Well I think so for peace of mind and the only way that you can see the condition of the self tapping screws that secure the coil to the element tubing, which will be plated steel on traps made before 1985 and therefore prone to corrosion. I changed all of the fasteners for stainless steel and put a new plastics kit on it, reassembled and set up on the tower. The results were good but it had taken a good few weeks work to put it back into good condition. I guess it should last for another twenty years or so.



Alas after using the TH3 MK3 for about nine months I decided to go for a three element SteppIR purely for the extra bands. The TH3 was mothballed until late May 2010 when a good friend on mine decided he would "take it off my hands", I now await the big signal from the man on the hill top G4UKP.

Below is the VSWR data.