144MHz Multiple Antenna System Setup for Contesting

(2013-09-14) PE1ITR
In VHF or UHF contests we always use a setup with 2 or more antenna systems like the picture below. Each antenna system is pointed by the operator to an area of interest. The transmitter power is divided to 2 or more power amplifiers. Each amplifier is connected to a antenna system. On receive the operator can switch the receiver to each antenna system. This way the qso rate can be increased.

The question is how the total system wil behave on transmit? In most cases the coax cable lenght to each system is random, the location of each system is random. There is no attention to phase diferences between the systems. Maybe the tx signal is canceled out in certain direcions. Who knows....... I decided to simulate this situation to see what the behavior is and learn from it.

The setup in the simulations. Two equal systems each with 2x stacked 9el dk9zb yagi's. One system at 15m agl, the 2nd system at 17m agl and they are 8 meters apart. The phase difference between system1 and system2 because of coax lenght is set to 90 degrees. Probably the worst situation. These numbers are a random choise like in real world.


Fig 1: left 2x10el K5GW yagi and right 2x9el DK7ZB yagi


Fig 2: The simulated situation in this case 30 degrees azimuth difference. Right system 1 @ 15m AGL, Left System 2 @ 17m AGL

Antenna Data
Performance15,49dBi @ 144.300MHz
Peak Gain15.49dBi
Peak F/B34dB
Stacking Distance3.4m (3.5 recommended)
2 Stacked Gain @ 3.4m spacing17,63dBi
2 Stacked F/B27.96dBi
Peak Gain Above Ground21.15dBi @ 15m AGL @ 2 degrees elevation
Boom Lenght4.980m

Table 1: Antenna data of a single system.
Simulation A

System 2 will turn from 180 to 0 degrees axmuth.


Fig 3: 180 degrees offset between the two main beams.


Fig 4: 135 degrees offset between the two main beams.


Fig 5: 90 degrees offset between the two main beams.


Fig 6: 45 degrees offset between the two main beams. The main lob gets distorted with 2db


Fig 7: 30 degrees offset between the two main beams. The mail lob shifts to the left and gain in dropping


Fig 8: 20 degrees offset between the two main beams


Fig 9: 10 degrees offset between the two main beams


Fig 10: 0 degrees offset between the two main beams


Lessons learned:
- Keep the antenna more than 45 degrees apart. Then the pattern of each system isn't much affected.
- When closer than 45 degrees the main lobs get distorted and is shifting from the heading.
- When the behavior of the systems is known. Some extra gain above one system to one direction can be achieved by playing with the azimuth. But watch out..



Simulation B

System 1 to 0 degrees azimuth and system 2 fixed to 20 degrees. System 2 feeding phase is changed from 0 to 360 degrees.
System 1 is pointing 0 degrees azimuth. System 2 is poining 20 degrees azimuth. Now we are feeding system 2 with a phase difference to system 1. The phase difference goes from 0 to 360 degrees in steps of 30 degrees.


Fig 10:



Fig 11: system2 phase = 0 degrees


Fig 12: system2 phase = 30 degrees


Fig 13: system2 phase = 60 degrees


Fig 14: system2 phase = 90 degrees


Fig 15: system2 phase = 120 degrees


Fig 16: system2 phase = 150 degrees


Fig 17: system2 phase = 180 degrees


Fig 18: system2 phase = 210 degrees


Fig 19: system2 phase = 240 degrees


Fig 20: system2 phase = 270 degrees


Fig 21: system2 phase = 300 degrees


Fig 22: system2 phase = 330 degrees


Fig 23: system2 phase = 360 degrees


Simulation C

Fixed offset between system A and B of 20 degrees and basisline distance is increased. Al lot of small lobs


Fig 24: baseline parameter



Fig 25: baseline = 8 meters


Fig 26: baseline = 8 meters


Fig 27: baseline = 10 meters


Fig 28: baseline = 12 meters


Fig 29: baseline = 20 meters

Simulation D

How does this show on a map? Fixed offset between system A and B of 20 degrees and basisline distance 8m.


Fig 30: Ant diagram to radio mobile

Simulation E

This simulation is more like the real situation at PC5T in the IARU 144MHz september 2013 contest. I identified to favorite direction of the antennas. Status A: System 1 to 100 degrees azimuth, System 2 to 160 degrees and System 3 to 270 degrees azimuth. and Status B: System 1 to 100 degrees azimuth, System 2 to 220 degrees and System 3 to 310 degrees azimuth.

First more about the status A situation.


Fig 31: Status A: Sys1 to 100, Sys2 to 160 and Sys3 to 270.



Fig 32: Status A Pattern. 0 degrees in picture = 100 degrees in real world



Fig 33: Status A Pattern plot into radio mobile software



Fig 34: qso map. Interesting is the dip around 120 degrees azimuth that also shows up in fig 32 and 33


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