I've got a pair of these UHF Yagis for HDTV, they appear identical and one picks up wonderfully, the other is about 1/2 the strength. I figure it's the BalUn but I have no idea (it's sealed but I don't mind cutting it open) how to test it. **broken link removed**
Ohm them both. If the flaky one has different dc resistances port to port than the good one, chances a winding has opened up. Google for balun to see how the windings are connected.
RF is weird esp at VHF and above. I'm convinced that many times a person just stumbles on something that seems to work and later comes up with the theory of why it works.
PS: doesn't seem like there is much to go wrong with that 'balun'. Have you tried to replace or swap the antenna leadwire/connector(s), that has been might biggest hitters on my external mounted stuff over the years, water/moisture is not good at these frequencies.
I should take it back, I just can't resist the hack. I would think a poor BalUn was a weak point and was hoping a $3 Radio Shack BalUn might help. I'll measure the two Yagi's tonight, see if I can spot a difference. I suspect it could be the wonky case design.
At that frequency you have a large cable loss in fact it there is a direct 90 degree bend in the co-ax it kills it. I would suspect corroded terminal connections. Lightning will open a balun but it can be checked with an ohm meter. A 3 DB loss could also be attributed to the termination which is probably 75 ohms.
Really I never heard about bends in the coax causing problems but doesn't hurt to straighten it out. The antenna is new and is attic mounted so corrosion isn't a problem. My curiosity will dissassemble it tonight and bust open the glue seal.