Comparing apples with oranges may lead that a banana is longer.
Differrent modeling software converge that gain of a 2 elements
optimized quad is not significatively different than gain of a two
element optimized yagi, more or less one dB. Moreover, there is no
reason why it should be different.
73,
Mauri I4JMY
---------- Initial Header -----------
>From : towertalk-admin@contesting.com
To : "Tower Talk" <towertalk@contesting.com>
Cc :
Date : Mon, 18 Nov 2002 22:48:55 +1300
Subject : [Towertalk] Quad vs Yagi
> I know of but one comparative study of quads and yagis in the field th
at 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 mount
ed telescoping tower.
> Comparison antenna could be used at same height on same site as test a
ntenna.
> Criterion was forward gain.
> Across the bands the trap tribanders looked rather bad. Away from opti
mum frequency the larger trap antennas often did worse than the referenc
e 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 mo
noband 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 witne
ss some exercises reported in QEX in recent years.
> (ii) The larger tribanders would have given better f/b and narrower be
amwidth compared to the smaller tribander even though forward gain was m
ediocre. This would give advantage on receive and if ample TX power was
available the overall communication capability of a staion so equipped w
ould be satisfactory to most users.
> (iii) The case Force 12 makes for horizontally stacked full length ele
ment tribanders is based on sound science.
> (iv) Da
suggests that the Cush
craft triband yagi with a log cell driven element is underperforming on
28mHz.
> (v) Speaking generally, as the good Dr Cebik shows, modern modelling p
rograms have good success in matching real world antennas of the sort un
der discussion.
> (vi) Claims of x% loss for various configurations should at least be s
upported 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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