Project
This is a typical
top loaded vertical. The antenna is too short for the operating
frequency and must be artificially made electrically longer by
adding a coil load at the base and a top loading capacitor
(horizontal wires) at the top. These short antennas are capacitive
at the base and the coil at the base is used to compensate for -X
and also electrically lengthen the antenna.
The coax to the
TX is on one side connected to the base of antenna, and normally
shield of coax goes to ground. This whole circuit including any
adaptation network etc... is replaced by a source placed at the
base of the antenna. So, if the antenna is fed at the bottom with
coax shield connected to the ground, the base of the antenna MUST
be connected to the ground.
Corrected the
original project to ground the vertical by putting a zero in Z and
removed a phantom load with 0s (which was not used anyway). This
below is the corrected project.
CM Radio Bloemendaal 1116 KHz
CE
GND Reference
UNITS Meters
Height 0.000
Over Ground 13 5 (Diel. - Cond. mS)
Radials 50 50
Boundary Circular
F 1.116
GW 0 10 0.000 0.000 25.000 11.700 0.000 25.000 0.005
GW 1 10 0.000 0.520 25.000 11.700 0.520 25.000 0.005
GW 2 10 0.000 -0.520 25.000 11.700 -0.520 25.000 0.005
GW 3 10 0.000 0.520 25.000 -11.700 0.520 25.000 0.005
GW 4 10 0.000 -0.520 25.000 -11.700 -0.520 25.000 0.005
GW 5 10 0.000 0.000 25.000 -11.700 0.000 25.000 0.005
GW 6 10 11.700 0.000 25.000 12.410 0.000 25.000 0.005
GW 7 10 11.700 0.520 25.000 12.410 0.000 25.000 0.005
GW 8 10 11.700 -0.520 25.000 12.410 0.000 25.000 0.005
GW 9 10 -11.700 0.520 25.000 -12.410 0.000 25.000 0.005
GW 10 10 -11.700 -0.520 25.000 -12.410 0.000 25.000 0.005
GW 11 10 -11.700 0.000 25.000 -12.410 0.000 25.000 0.005
GW 12 10 0.000 0.000 25.000 0.000 0.000 24.290 0.005
GW 13 10 0.000 0.520 25.000 0.000 0.000 24.290 0.005
GW 14 10 0.000 -0.520 25.000 0.000 0.000 24.290 0.005
GW 15 30 0.000 0.000 0.000 0.000 0.000 24.290 0.005
GW 16 20 16.000 0.000 0.000 16.000 0.000 30.000 0.200
GW 17 20 -16.000 0.000 0.000 -16.000 0.000 30.000 0.200
S 1 154 100 0
LP 1 154 0 1328 0
Coax 50
Results of NEC4WIN95
Model
Impedance
Antenna Height is : 0 m (0ft)
Ground Diel. = 13 Cond. = 5
50 Radials of 50 m ( 164.042 ft)
Frequency : 1.116 MHz
Wave Length : 268.638 m (881.358 ft)
Load # 1 = 0.000E+00 +j 9.312E+03 at Pulse 154
IMPEDANCE = 7.59 + j 9199.67 Ohms at Source 1
SWR = Infinite
Voltage = 100.00 + j 0.00 at Pulse 154
Current = 0.00 - j 0.01 Amps
Power = 0. WATTS
The antenna is highly inductive
which seems odd. The 1328 microHenries coil must be wrong somehow
unless the adaptation box is some sort of L network that will
eliminate this high +X.
After running the optimizer to
resonate the antenna the best L for Z = 7.59 + j 0.09 Ohms
was 16
micro Henries.
Antenna Height is : 0 m (0ft)
Ground Diel. = 13 Cond. = 5
50 Radials of 50 m ( 164.042 ft)
Frequency : 1.116 MHz
Wave Length : 268.638 m (881.358 ft)
Load # 1 = 0.000E+00 +j 1.124E+02 at Pulse 154 <<<
with 16 µH
IMPEDANCE = 7.59 + j 0.09 Ohms at Source 1
SWR = 6.59
Voltage = 100.00 + j 0.00 at Pulse 154
Current = 13.17 - j 0.15 Amps
Power = 658.64 WATTS
Note:
This will not influence the pattern and gains very much.
Pattern, Gain, Take off angle
Gain is 4.39 dBi, Take Off angle
is a very low 13 degrees
Nothing abnormal about this. Gains
calculated by NEC4WIN95 (Mininec) for short verticals are know to
be shlightly "optimistic" and gain will be 2 to 2.5 dBi
lower in practice.
NEC2 Model
The corrected
NEC4WIN95 model was converted to NEC2. I kept the same L and
didn't use the 16 µH but the original 1328 uH.
Converted model
CM
CM NEC4WIN95 File
CM Radio Bloemendaal 1116 KHz
CE
GW 1 10 0.00 0.00 25.00 11.70 0.00 25.00 0.00250
GW 2 10 0.00 0.52000 25.00 11.70 0.52000 25.00 0.00250
GW 3 10 0.00 -0.52000 25.00 11.70 -0.52000 25.00 0.00250
GW 4 10 0.00 0.52000 25.00 -11.70 0.52000 25.00 0.00250
GW 5 10 0.00 -0.52000 25.00 -11.70 -0.52000 25.00 0.00250
GW 6 10 0.00 0.00 25.00 -11.70 0.00 25.00 0.00250
GW 7 10 11.70 0.00 25.00 12.41000 0.00 25.00 0.00250
GW 8 10 11.70 0.52000 25.00 12.41000 0.00 25.00 0.00250
GW 9 10 11.70 -0.52000 25.00 12.41000 0.00 25.00 0.00250
GW 10 10 -11.70 0.52000 25.00 -12.41000 0.00 25.00 0.00250
GW 11 10 -11.70 -0.52000 25.00 -12.41000 0.00 25.00 0.00250
GW 12 10 -11.70 0.00 25.00 -12.41000 0.00 25.00 0.00250
GW 13 10 0.00 0.00 25.00 0.00 0.00 24.29000 0.00250
GW 14 10 0.00 0.52000 25.00 0.00 0.00 24.29000 0.00250
GW 15 10 0.00 -0.52000 25.00 0.00 0.00 24.29000 0.00250
GW 16 30 0.00 0.00 0.00 0.00 0.00 24.29000 0.00250
GW 17 20 16.00 0.00 0.00 16.00 0.00 30.00 0.10
GW 18 20 -16.00 0.00 0.00 -16.00 0.00 30.00 0.10
GS 0 0 1.000
GE 1
GN 0 50 0 0 13 .005 50 .002
FR 0 1 0 0 1.12 0.0
LD 0 16 1 1 0 1328E-6 0
EX 0 16 1 00 100.00 0.00
RP 4 181 1 1000 -90 0 1 1
RP 4 1 361 1000 90 0 1 1
EN
Impedance and Gain
At 1.120 MHz Z = 10.613 + j 9261.330 Ohms
which is close to NEC4WIN95 Z =
7.59 +j 9200 Ohms
Gain is as expected some 2 dBi
lower at 2.55 dBi and Take off angle is higher at 23°.
Moving one mast away 6 meters
Mast at X=16m moved to 22m
(wire 17)
Wire 17: 22.000 0.000 0.000 22.000 0.000 30.000 0.200 20
New Impedance:
Antenna Height is : 0 m (0ft)
Ground Diel. = 13 Cond. = 5
50 Radials of 50 m ( 164.042 ft)
Frequency : 1.116 MHz
Wave Length : 268.638 m (881.358 ft)
Load # 1 = 0.000E+00 +j 9.312E+03 at Pulse 154
IMPEDANCE = 8.25 + j 9197.25 Ohms at Source 1
New field
Field is not changed much. In fact it
increased from 4.39 to 4.42 dBi by moving the pole 6 meters away!
NEC2 simulation
With one pole at 22m instead of 16 Z = 10.557 + j 9259.260 Ohms
New max field is 2.89 dBi in NEC2 compared to previous
2.55 dBi so NEC2 confirms that Far
Field is increased by moving the pole away.
