Brian Sharrock wrote:
"Adrian" wrote in message
...

[...]

Let that be a lesson to me; I assumed that it must be a Yagi. After all,
that's what _everybody_ uses. I re-read your ' ... not a Yagi' and
thought; - "No! they couldn't use that type ... could they?"

[...]
The groundng effect of a lump of steel shouldn't hurt it too much.
'Theoreticaaly' the reflector is the minimum area that one can 'get away
with' . Additional material, provided it's behind the dipoles, shouldn't
matter.

RF energy is what 'we' call 'funny stuff' (another technical term ) bits of
cable, such as co-ax, that seem to be normally resitsive become 'open
circuit' and/or 'dead short circuit' at different points along the cable
once one starts trying to stuff rf energy along it: technically it's all to
do with lambda and halve and quarters but as lambda changes with frequency
it all get too hard for humnas to suss out. { partly becaue it's all tto
hard to imagine 'receiving' things off an aerial - we utilise the theory of
reciprocity and pretend that the aerial is a transmitter }
Your Irish installers seem to have attempted to install a phased array,
wherein one dipole will 'interfere' with it's adjacent neighbour cauisng
nulls and maxima to overlap creating a narrowing of the beam without
significantly increasing the received signal .

[...]

Maybe this has been clarified earlier in the thread ...

It seems likely to me that the OP's aerial is a 'stacked dipole array'
as shown in Fi.g 5 of:
http://www.wrightsaerials.tv/digitalterrtvrecep.htm. They used to be
marketed under the product name 'Colour King' (I've forgotten the
maker). I have seen them on relatively new houses here in the Donegal
area --- which is hilly and has otherwise marginal reception from
across the national border. But, as someone speculated, it could be
that they are used because they happen to be surplus stock.

They used to be used a lot in Ireland for 'extremely long distance
reception' (my term), e.g. receiving BBC, ITV in the Irish midlands ---
order of 50-70 miles from the transmitter in the Mournes. You would see
them atop gynormously high masts. Incidentally, compared to what went
before (huge Yagi-like arrays --- Hirschmann brand --- that weighed a
ton), they seemed to be machanically less fragile and offered less wind
cross-section. After the stacked dipole array, the same areas switched
to what appeared to be a single dipole design, with a dish shaped mesh
reflector. Now, of course, everyone in those regions use satellite or
cable.

(Regarding terrestial reception.) If the OP is in a flatish area, then
find a neighbour with good reception and do as they do --- same aerial
type, some band (colour coded?), same polarisation. It could be that
you can experiment with aerial mounted on something easily reachable
from the ground; five miles from the transmitter was mentioned, I
think. If you are in a very undulating area, then all bets are off. As
others have noted, skilled aerial installers may be hard to find; for
that reason alone, you should be prepared to pay decently for a decent
job done, and a job that will last. Installing an aerial on a chimney
is easily d.i.y. But you may not have ladders and a head for heights.

Best regards,

Jon C.