I know of but one comparative study of quads and yagis in the field that =
seems to me to meet scientific standards.
Cannot remember the reference, but it was in Ham Radio a long time ago.
Method:
Two element trap tribander used as comparison antenna with truck mounted =
telescoping tower.
Comparison antenna could be used at same height on same site as test =
antenna.
Criterion was forward gain.
Across the bands the trap tribanders looked rather bad. Away from =
optimum frequency the larger trap antennas often did worse than the =
reference antenna.
Two element quads did better than monoband yagis of same boom length, in =
line with theory which predicts ca 1.8 dB better.
Longer multielement quads tended to underperform by comparison with =
monoband yagis of the same boom length.
Note:
(i) This was before antenna modelling programs were widely available. It =
may be possible to optimise the performance of longer quads, as witness =
some exercises reported in QEX in recent years.
(ii) The larger tribanders would have given better f/b and narrower =
beamwidth compared to the smaller tribander even though forward gain was =
mediocre. This would give advantage on receive and if ample TX power was =
available the overall communication capability of a staion so equipped =
would be satisfactory to most users.
(iii) The case Force 12 makes for horizontally stacked full length =
element tribanders is based on sound science.
(iv) Data published in RSGB Radio Communication suggests that the =
Cushcraft triband yagi with a log cell driven element is underperforming =
on 28mHz.=20
(v) Speaking generally, as the good Dr Cebik shows, modern modelling =
programs have good success in matching real world antennas of the sort =
under discussion.=20
(vi) Claims of x% loss for various configurations should at least be =
supported by data from modelling if they are to be taken seriously.=20
73 =20
Barry
end
Barry Kirkwood PhD ZL1DD
Signal Hill Homestay
66 Cory Road
Palm Beach
Waiheke Island 1240
NEW ZEALAND
ph/fax 64-9-372-5161
www.waiheke.co.nz/signal.htm
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