In message , writes
That's a handy site, I've been looking for 2.5 inch V brackets at a price
without exhorbitant postage. I put up a TV aerial on a 10ft pole on T&Ks on
my side wall recently. I've been since inundated with marauding crows,

Crows can be a radio engineers best friend too.

I had a PMR base on a site with a 100 foot tower in Nottingham and the
customer complained of intermittent poor range. I went up there twice
and checked the base and the aerial were OK. The aerial I swept from
ground level and it checked OK. On the third visit I was getting the
same results and beginning to suspect foul play, the customer had a few
enemies and had in the past had his system jammed. Any way all of a
sudden the aerial showed a fault for a couple of seconds, this happened
2 or 3 times in quick succession. Standing in the doorway of the site
hut and looking up a crow was perched on top of the aerial and every
time it took off the aerial, 3m long fibreglass tube waved about. I
thanked the crow for its help and ordered a new aerial.

On the subject of chimneys I would go for

http://www.aerialshack.com/aerial-ch...ger-aerials-p-
497.html

it is more expensive but will withstand the loading the OP has in mind
with no problems at all and although it still has only one lashing wire
it has more metal against the stack and will be less prone to twisting,
not that the first one mentioned probably would either. But this
definitely would not.

Within reason try and get the aerial as high above the chimney as
aesthetics will allow, this will give a better take off, especially if
you have neighbouring chimneys and roofs near by.






--
Bill