"Alan Peake" wrote in message
...
Hi all,
I seem to recall a while back, someone posting an article about
stopping birds - parrots in particular - from nibbling away at coax and
insulated wires. One of our local club members has 4X10 on 2m and 4X15 on
432 MHz. We discovered that ALL of the 4:1 coax baluns had been chewed -
some to the point that they were not connected to the yagis at all! Some
of the baluns had sections completely missing. Amazingly enough, he still
seemed to get out. Anyway, we have temporarily replaced the baluns but we
need to find a way of preventing a reoccurrence of parrot pecking. All
ideas and thoughts considered - sensible ones of course
73 de Alan

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

"Tam/WB2TT" wrote in
:

....
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.

Birds attack Heliax at this location, but less so than vinyl covered
coax.

Sulphur crests are a particular problem:
http://en.wikipedia.org/wiki/Sulphur-crested_Cockatoo

Nevertheless, Heliax is pretty much unaffected as they usually rip small
holes in the vinyl sheath which doesn't affect the cable due to the solid
external conductor, and even when they punch through the copper shield,
water will not soak throught the cable due to the closed cell foam that
is bonded to the shield with adhesive.

There might be more creative solutions Alan. I stopped feeding birds when
Sulphur Crests starting congretating en-masse and before they started
eating the house.

Owen

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

"Alan Peake" wrote in message
...


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

It is a 200 Ohm antenna. Each half is 100 Ohms to ground.When you put the 2
sides together you get 50 Ohms. Since the line is 1/2 wave long, any
impedance will work, including 50. CushCraft made a beta match 6 meter beam
which used a 1/2 wave section of RG11 75 Ohm coax. People have also use 93
Ohm coax, but its loss at 1:1 SWR is probably more than RG8 at 2:1 .

Tam

It is a 200 Ohm antenna.
So it is. Anyway, the question arose as I'd never seen anything other
than 50 ohms used for the balun.
Anyway, I spent all day on the 8 baluns (4 for 432 MHz and 4 for 144
MHz) and did as Owen suggested - put 1" PE irrigation pipe over the
baluns. Let's see the little so-and-sos eat through that!!
Alan