4O3A Triplexor

Dummy Load

Until today, I’m fascinated what can be achieved with good filters. At our Contest Station ED1R we bought a Triplexor (10m/15m/20m) in order to be able to use our new Optibeam OB11-3 on the three bands simultaneously.


At ED1R we only have one tall tower with 20m height. While we are able to finish in contests within the Top10 of our category, results showed that the highbands need to be boosted to get a permanent seat in the Top3 ranks. Since Vertical steel equity is restricted, we thought that a big Tribander on top of the tallest tower with a 4O3A Triplexor would give us the biggest bang for the buck.

4o3a triplexor

After the successful installation of the Triplexor, each of the three highbands (10m / 15m / 20m) has now 3 Antennas available:

  1. Rotatable Monobander
  2. Monoband Yagi fixed towards USA or EU
  3. OB11-3, connected through the triplexor


The schematic below shows the setup:

triplexer at so2r with switching

A prerequisite for the Triplexor is a set of High Power Bandfilters. Achieving >100dB attenuation on a harmonic band is quite and engineering challenge. In order to ensure proper operation, the input terminals of the Triplexor have to be terminated at any time with 50Ohm. Therefore I built three switchable dummy loads.


The picture above shows the Triplexor mounted on a timber panel with the three switchable dummy loads


The switchable dummy load consists mainly of a 50Ohm/100W RF resistor, connected to a heatsink and a 16A/230V relais. If no power is applied, the input terminal from the Triplexor is always connected to the load. For wiring high power Teflon cable has been used. An LED indicates the usage.


This shows the new antenna switching system of ED1R. Four homebrew Stackmatches, a 10×2 Antenna switch, the 4O3A High power Bandfilters and the 4O3A triplexor.

ed1r_antenna switching

Same setup, just with all wires connected

ED1R Stackmatch Controller

I updated and included the Dummy-Load switching into the software of our Microcontroller based Stackmatch Controllers. Now the relays inside the load will be triggered whenever the OB11-3 is selected.

Triplexor in Action

After the successful installation, Javi, EC4DX recorded a short video to demonstrate the performance of the Triplexor. Unfortunately we missed to recored the harmonics on 10m while transmitting on 20m. But the video gives you anyhow a good idea about how smooth it works.


I invested in design, hardware and software roughly 40 hours during various evenings and weekends. Ranko’s Triplexor is a truly great invention. Except of a small portion (+-20kHz) of the 20m’s harmonic on 10m, almost no interference can be noted. It’s almost a bit spooky to send 1,5kW on 10m and 15m though a coax cable while listening listening on 20m with the same antenna.

About Tobias (DH1TW)

Self-confessed Starbucks addict. Loves to travel around the globe. Enjoys the technical preparations of Amateur-Radio contests as much as the contests themselves. Engineer by nature. Entrepreneur. For more, follow him @DH1TW


  1. Using 230 V relays is NOT healthy! How warm 50 Ohms dummies get? USA triplexer has just three serial resonant circuits. GL wih Monte Negro tech 🙂

    P.S. I have to use Firefox for your Bavarian postings and RBN!

    • Hi Mario,
      why not? 2kW at 50Ohm results in approx. 6,3A. Even considering the Skin and other RF effects, this should leave plenty of margin. There are a lot of commercial designs (e.g. WX0B or Microham) which use standard 16A/250V relays.

    • OM mixed up contacts rating with coil voltage 🙂 How warm are dummies?

    • I haven’t checked the temperature of the dummies – but I estimate that 100W is very very conservative. I don’t expect ever to feel a warm dummy. Next contest I’ll check and let you know!

  2. Bostjan S55O says:

    We use the same combination at the S51A station. It works good and smooth, you just need to have good chokes on the antenna and good grounding of the whole sistem. There is an error on the 4o3a schematics, the 1×2 switches with the 50 ohm should be turned around, so when the input for a band (10/15/20) is not used, the triplexer switches to a 50 ohm dummy termination on that port.

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