At 10:54 AM 2/25/97 -0500, you wrote:
>In a message dated 97-02-24 18:05:13 EST, you write:
>
><< Anyone using the 204BA been successful in modifying the dimensions in
> the interest of improving performance? Keeping the same approximate boom
> length that is. Interest is all mode operations in contesting. >>
>
> The 204BA was the only antenna that Jim Lawson, W2PV, well-known
>ground-breaking antenna designer and station builder, couldn't improve.
> Check out his book "Yagi Antenna Design" for more info.
>
>73, Steve K7LXC
W2PV's work was pace setting and helped to bring about the
revolution in the antenna modelling world as we now know it.
But the 204BA can be improved considerably, if you are willing
to change both element spacings as well as lengths.
And from the original question I would assume that this
is an option.
The definition of improved performance may mean different things
to different people. Helping the VSWR bandwidth is a big
improvement to me because I run Alpha 87As and they are
much happier with low VSWR than many other amps--so
my definition may be different than someone else's.
The enclosed dimensions make for a much better antenna
as far as I am concerned. Same gain (well a tad more
for CW and a tad less at the top of the phone band),
better F/B, and much better VSWR BW. What is the tradeoff?
A more unbalanced antenna, but with cross-flow principles
the question is just one of mounting the boom in the
middle and adding weight to one end.
73 John W0UN
Performance comparison:
W0UN version 204BA
Freq 14.0 14.2 14.35
Gain dBi 8.06 8.12 8.20
F/B 20.87 26.62 25.53
VSWR 1.03 1.07 1.18
Hy-Gain 204BA
Freq 14.0 14.2 14.35
Gain dBi 7.98 8.19 8.33
F/B 14.45 22.48 24.91
VSWR 1.55 1.06 1.54
------------------W0UN 4L 20M antenna based on HG 204BA parts-------------
W0UN version of the Hy-Gain 204BA
14.000 14.200 14.350 MHz
4 elements, inches
5.0000 1.2500 1.1250 0.8750 0.6250 0.4375
0.0000 3.6250 41.8750 46.0000 50.5000 24.0000 55.4231
81.7524 3.6250 32.3750 46.0000 50.5000 24.0000 50.0136
128.1037 3.6250 18.3750 46.0000 50.5000 24.0000 62.2143
302.0631 3.6250 14.1250 46.0000 50.5000 24.0000 49.2473
Effects of the element-to-boom clamp and boom
have been modeled here by a cylindrical taper
section 3.625" long and 5" diameter. The clamp is
7.25" long by 3.25" wide and passes the element
through a 2"-diameter boom.
--------original HG 204BA model (for reference)-------------
Model Verification, Hy-Gain 204BA
Height 1020.000
14.000 14.200 14.350 MHz
4 elements, inches
5.0000 1.2500 1.1250 0.8750 0.6250 0.4375
0.0000 3.6250 41.8750 46.0000 50.5000 24.0000 50.0000
122.8750 3.6250 32.3750 46.0000 50.5000 24.0000 50.0000
211.6250 3.6250 18.3750 46.0000 50.5000 24.0000 51.0000
307.2500 3.6250 14.1250 46.0000 50.5000 24.0000 49.0000
Effects of the element-to-boom clamp and boom
have been modeled here by a cylindrical taper
section 3.625" long and 5" diameter. The clamp is
7.25" long by 3.25" wide and passes the element
through a 2"-diameter boom.
This YO model agrees fairly well with pattern
measurements made on the Hy-Gain antenna range of a
production 204BA (reflection-corrupted patterns).
Approximate F/B measurements (180-deg backlobe):
14.0 MHz 12 dB 14.2 MHz 17 dB 14.4 MHz 26 dB
14.1 14 14.3 21
John Brosnahan
La Salle Research Corp.
24115 County Road 40
La Salle, CO 80645 USA
voice 970-284-6602
fax 970-284-0979
email broz@csn.net
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