A Bit OT - Satellite & Terrestrial TV in West Cork, Ireland
HI Brian / Andy
On Tue, 17 Oct 2006 08:38:09 GMT, "Brian Sharrock"
wrote:
"Christian McArdle" wrote in message
. ..
The existing aerial's a sort of '4 dipoles and a single mesh
reflector' arrangement - not a Yagi
Can you identify it? 95% of all TV aerials are Yagis. (And 95% of
statistics are made up on the spot).
Christian.
Chipping in, again, I can't quite parse what you're saying; is the aerial
array; -
query
Case A:
-- -- -- -- four off dipoles
--------------------------- mesh reflector
Yes - that's the one !
or;-
Case B:
--
--
-- four 'dipoles' = one dipole
and three directors(?)
--
------------- mesh reflector
/query
No - no directors, just cunningly-phased dipoles and a mesh reflector.
Low-gain, wide-angle - methinks
In both Case A and Case B the transmitter is normal and on the 'dipole' side
of the mesh. BTW, the 'mesh' (reflector) is theoretically infinitely large
and stops all signals from behind ... luckily for us, the Lord ensured that
the reflectors could be attacked with tin-snips and didn't need infinite
dimensions; turns out that one only _needs_ the reflector to be this* big
and the mesh only has to be this* far behind the dipoles
[*this is a function of frequency]
Case B would be normal and what RTE intend when they call for a UHF Band A
aerial; CASE A is highly unusual - what RF Engineers describes as a phased
array
with 'intriguing' possibilities of gain, bandwidth and beamwidth as a
function of frequency!
Even better if the mesh is electrically connected to the gurt big
I-beam (by virtue of being physically in contact with it !
Had a quick discussion with the installers today and suggested that I
might be interested in paying their bill if they might be interested
in coming back and doing a proper installation...
...we'll see....g
Thanks
Adrian
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