Antennas, simulations, antennas related projects and information.

Top Loaded vertical
for 1.2 MHz

 

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 H
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 H 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.

 


This document is Copyright 2003-2005 ORION Microsystems