[TowerTalk] TH7 problem

[Eddy Swynar]

On 2011-06-23, at 1:22 PM, Radio K0HB wrote:

> My TH7 recently (and suddenly) shows 2:1 SWR on 15 & 20m.  OK on 10m.  My reaction is a bad 15m trap.  Probably in a parasitic element, not a driven one? I’d like to only need to make one trip up the tower with the right parts, so any other possibilities?  No obvious damage from the ground.
> 
> Comments?


Hi Hans,

I had the very same thing happen here with my old Hygain TH3-Mark III three element tri-bander, i.e. suddenly the SWR was A-OK (i.e. unchanged) on 10, but sky high on 15 and 20 meters...

Well, maybe I shouldn't say sky high: the 1:1 SWR points on those latter two bands had shifted UPWARD by some 120 KHz, or so, and the antenna had a very narrow bandwidth on them (all three bands were originally optimized for the CW ends of the bands).

Curiously enough, just as quickly as the malaise infected the antenna, in a few short days it completely disappeared! I suspected that maybe I had rain intrusion in one of the driven element traps, so I monitored the SWR both on wet rainy days, & sunny dry ones---no change.

Maybe I had a nest of hornets, or spiders, that were attempting to take refuge inside one of the traps, & the RF "zapped" them...? I don't know. I'm just glad the thing is working well...well, for NOW, anyway! Hi Hi.

~73~ de Eddy VE3CUI - VE3XZ