Hi All:
I hope everyone got the article on radiation EFF.
About multi-el Quads. The trick is in spacing and reducing the director
sizes out to the fourth director. The Driven is resonated first and then
matched if needed. The reflector size will normally be larger than the old
formula was.
Boy I sure am glad this removed you gentlemen from the politic subject.
Bill (yes I manufacture Quads ) Wall KC4UZ
----- Original Message -----
From: "Barry Kirkwood" <bjk@ihug.co.nz>
To: "Tower Talk" <towertalk@contesting.com>
Sent: Monday, November 18, 2002 4:48 AM
Subject: [Towertalk] Quad vs Yagi
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.
(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.
(vi) Claims of x% loss for various configurations should at least be
supported by data from modelling if they are to be taken seriously.
73
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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