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achieving more gain by stacking/baying two large UHF aerials

Von: wrightsaerials@aol.com (wrightsaerials@f2s.com) [Profil]
Datum: 06.05.2010 02:56
Message-ID: <6be0c8ab-80aa-45b7-96b8-3d3e79b12e0b@q32g2000yqb.googlegroups.com>
Newsgroup: uk.tech.digital-tv
Today I installed two Vision 76 element aerials, vertically polarized,
side by side and about a metre apart. I needed the extra directivity
this gives, but I was also interested in the gain. Vision sells a
'combiner/balun' as part of their stacked log periodic kit. This
contains nothing but PCB tracks commoning the two inputs and the
output, so whether it has any  function as a matcher I don't know. I
tried this device with the two 76 element aerials, which of course is
not what it's sold for.

I measured all 11 signals from Crosspool, and averaged the results.
There no were no big deviations or peculiarities in each sequence of
figures.

Taking the average of the signal from each of the two aerials as 0,
the gain achieved by stacking two was as follows:

Taylor 2 way splitter: 1.9dB
No combiner/matcher*: 2.1dB
Vision combiner: 1.3dB

*No combiner/matcher: the two feeders were connected together with a
soldered joint. It's interesting that even with a 2:1 mismatch the
gain is slightly better than with a splitter. I expected very strange
results with this method of combining, but the gain was fairly
consistent across the channels.

When Iíve stacked Blake 18 elements and various logs Iíve usually
managed to get a bit more gain Ė around 2.7dB on average. I donít know
why these figures are lower than that. I've never stacked two of these
big Vision aerials before. I'll experiment further.

The actual result of this installation was pretty impressive. These
big Vision wideband aerials do seem to work very well (for a wideband)
and stacking two of them gave a really worthwhile improvement on the
previous aerial, which was an 18 element wideband. Signal levels were
8 to 13dB better, BER on the difficult muxes went from marginal to
perfect, and there was no visible ghosting on the analogue channels.
The last was a real surprise.

Bill


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