Heliax or semirigid coax might cause them to give up. Especially the latter.
75 Ohm stuff would be fine for the 4:1 balun, because you actually would
want it to be 100 Ohms.

Tam/WB2TT



100 ohms? This is just a half-wave coax balun. All the books say it
should be 50 ohms - same as the feed and the yagi. The only place where
a different Zo is used is where the four yagis combine. There, a
quarterwave section of TL of Zo=25 is used to match the 12.5 ohms of the
four yagis in parallel to the 50 ohm main feeder.
The main feeder is heliax so the birds haven't got to that - yet. (Tough
birds down here in VK!!)

Alan