Having already a delta loop antenna in place, I wanted to see how a parasitic 2 elements array would perform.
Step 1 – MMANA-GAL antenna software design.
Goal: 2 switchable directions , relative high F/B ratio and decent gain at 5 degrees take off angle.
Since I was limited to 6 meters spacing between antennas and no more than 9.4 meters height , had to simulate values accordingly in order to get the max out of it for DX purposes (gain at lower takeoff angle).
Actual configuration is 2 poles about 11 meters made by 2 x 3 x 48x48x4000 wooden studs overlaped just about 70 cm one over the other and 12 wood screws.
Each triangle has 12.36 meters for sides and 19.8 meter for the base.The base is at 2 meter up from the earth and the top corner is at 9.4 meter height.
6 guy ropes for anchors and 2 small pulleys for wire traction located at the top of the pole and one corner of triangle.
Each antenna would have a plastic box fitted wit PL-259 female connector with hot pin connected to one side of triangle and metallic case to base of triangle.
2 coaxial stubs are required to achieve about 1 microHenry when shorted, so using LMR400 with 0.83 velocity factor I needed about 4.1 meters long each stub.If using RG213 then velocity factor is 0.67 and stub lenght would be 3.3 meters long.
Each antenna via stub goes to another central relay plastic box also fitted with 3 female PL259 connectors and a 12 V jack for sending 12V for East and no Voltage for West.
Central box has 4 relays connected in such manner that if transceiver goes to East antenna via 2 relays, then the other 2 relays will shorten West antenna so it will behave like a reflector and viceversa for the other direction.Most important is not use metallic box since shorted stub has to be ungrounded.
Take good care for both antenna symmetry , and if using 2.5mm insulated wire then some adjusting may be needed.(I cut about 1/2 meter from each wire helped by my Rigexpert antenna analyzer )
The results are as simulated in software: 50 ohms with allmost zero reactance, Front to Back ratio about 15 dB and low takeoff angle.
Using 100 W i was able to easily contact JA , VK with antenna firing towards East, and K, V44, E29 with antenna firing towards West.
Running 1 K was more spectacular , like one shout and dx station was instantly responding to me from ll pile-up and also Reversebeacon website shown great values for my callsign.
In the video below, the sudden 3 points S fading is due to switching array East or West for comparison.
Pay attention to chokes , as 12 V remote cable for switching direction would get RF energized so common mode chokes have to be put in place.
For all hams looking for low height and good dx results, 2 elements delta loop is quite ok since a 2 or 3 elements yagi at same height would produce lower results and also similar values can be obtain from 4 square vertical antenna but more complicated to build(lots of radials, 4 poles, a lot of space , etcetera.)
Mmana-gal file download here … after download rename the extension from txt into maa. The 1 uH coil from the design is made by coax stub described above.
The overall cost for this antenna would be about 100 Euros give or take.
73 and good luck building it!
Here is another F/B ratio video sample after I mounted common mode choke, about 4 S points difference.