40 meter East-West switchable 2 elements delta loop antenna array

2020 September 19 Update.

Very unstable antenna depending by ground humidity. This year I simply could not replicate it even though same wires / poles and location used.


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!

Gabriel yo8rxp

 

 

Here is another F/B ratio  video sample after I mounted common mode choke, about 4 S points difference.

 

4 thoughts on “40 meter East-West switchable 2 elements delta loop antenna array

  1. Proiect frumos si interesant. MMANA GAL chiar si imperfect este arhisuficient pentru astfel de proiecte. Performanta rezonabila pentru costurile implicate desi inerent limitata de concept (BW redus, deschidere de 80 de grade @3dB, eficienta de radiatie redusa serios de pierderile de tip ground loss datorate apropierii de sol – rezistenta de radiatie mica in raport cu cea de pierderi). Succes pe mai departe.
    73 de Morel 4X1AD ex.YO4BE

    P.S.: Atentie la coeficientul de velocitate in cazul folosirii de cabluri coaxiale chinezesti ieftine. Trebuie masurate fizic deoarece de multe ori nu te poti baza ca specificatiile de facto sunt identice cu cele generice (o spun din experienta mea profesionala).

    1. Merci mult Morel de comment.Adevarat ca apropierea de sol genereaza pierderi masive, mai mult de atat este o antena instabila in functie de umiditatea solului.
      Factorul de velocitate a fost masurat cu analizorul inainte de montajcaci intradevar, diferiti producatori diferite valori.
      73 si mult succes

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