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In my report by e-mail of 15 September
1999 19:19 top loads with 0, 1, 2 and 4 wires, both horizontal and sloping
down under 45 degrees, were discussed.
In report by e-mail of 16 September 1999
13:48 top loads of 2, 3 and 4 parallel horizontal wires were the
subject.
In this (the last I hope for you ...)
report you find the results of computer simulation of a coil between the top end
of the vertical radiator and the top load wires.
To limit the number of cases only antennas
with top loads of 2 times 5 m, 10 m and 20 m and 4 times 5 m, 10 m and 20 m were
modelled. The wires are horizontal.
Also one antenna with 2 x 5 m top load
wires drooping down under 45 degrees has been modelled.
For practical reasons a top load coil has
to be of limited size. I have modelled coils of 500, 1000 and 2000
microhenry.
In order to present a more useful picture I also included a
loading/tuning coil at the bottom end of the radiator. The coil has been chosen
so that it resonates the system. The Q of both coils has been set at
300.
The total loss resistance now includes that of wires and coils
and the efficiency becomes
{radiation resistance/(radiation
resistance + wire resistance + coil resistances) } * 100%.
For the efficiency of the complete antenna system the earth
resistance must to be included. But as this adds the same amount to the
resistance of wires and coils, in all cases the efficiency as given can be used
as a figure of merit.
Note that this is not the case in
the two previous reports because the loading/tuning coil and its loss were not
included in the modelling.
The vertical part of the antennas is again 10 m long and the
wire size is 1.5 mm diameter copper.
Number and length Top
coil Bottom
coil Radiation resistance Loss resistance
Efficiency
of top loading wires
microhenry microhenry
milli-ohm
ohm
%
2 x 5
m
0
11564 16.
7
33.3
0.05
2 x 5
m
500
11443
16.7
33.3
0.05
2 x 5
m
1000
11278
16.7
33.3
0.05
2 x 5
m
2000
11021
20.0
33.3
0.06
2 x 10
m
0
7897
22.8
22.8
0.10
2 x 10
m
500
7677
22.9
22.9
0.10
2 x 10
m
1000
7449
22.9
22.9
0.10
2 x 10
m
2000
6970
23.0
23.0
0.10
2 x 20
m
0
4812
26.6
14.0
0.19
2 x 20
m
500
4490
26.8
14.1
0.19
2 x 20
m
1000
4156
26.8
14.1
0.19
2 x 20
m
2000
3442
27.4
14.4
0.19
4 x 5
m
0
8590
22.3
24.8
0.09
4 x 5
m
500
8380
22.3
24.8
0.09
4 x 5
m
1000
8163
22.4
24.9
0.09
4 x 5
m
2000
7707
22.5
25.0
0.09
4 x 10
m
0
5261
26.0
15.3
0.17
4 x 10
m
500
4943
26.0
15.3
0.17
4 x 10
m
1000
4612
26.2
15.4
0.17
4 x 10
m
2000
3905
28.3
15.7
0.18
4 x 20
m
0
2896
29.1
8.53
0.34
4 x 20
m
500
2494
29.2
8.56
0.34
4 x 20
m
1000
2073
30.4
8.65
0.35
4 x 20
m
2000
1169
31.8
9.05
0.35
4 x 5 m under 45
degrees
0
9233
16.0
26.6
0.06
4 x 5 m under 45
degrees
500
9023
16.0
26.7
0.06
4 x 5 m under 45
degrees
1000
8805
16.0
26.7
0.06
4 x 5 m under 45
degrees
2000
8342
1
.1
26.9
0.06
Conclusion: A top coil does not increase efficiency for the configurations
modelled.
73, Dick, PA0SE
D.W. Rollema
V.d. Marckstraat 5
2352 RA Leiderdorp
The Netherlands
Tel. +31 71 589 27 34
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