Construction project 2m/70cm duplexer

Homebrew 2m/70cm duplexer for 23 and 13cm SOTA activations. Why buy one when you can make your own?

VK1AD 2m/70cm duplexer

All components are mounted on a single sided copper clad board.

I will use my FT-817 at 1 watt to drive the 23 and 13cm transverters via the duplexer. The duplexer will permit instant band chages. SG-Lab transverter IF input frequencies are:

  • 23cm (1296.150 MHz): IF = 144.150 MHz
  • 13cm (2.403150 GHz): IF = 435.150 MHz

Test instruments used; NanoVNA, RigExpert AA600 antenna analyser, Diamond SX40C VSWR meter and a wideband IC-R20 receiver. You will require two 50 ohm dummy loads.

The NanoVNA is a handy RF signal injection source which was injected in to the duplexer output and input ports and non-scientifically measured using the IC-R20 S-meter. The IC-R20 antenna socket is connect to the corresponding duplexer BNC socket via a short length of 50 ohm coax. I had to reduced the IC-R20 RF antenna gain to ‘minimum’ and activate the RF attenuation option.

I adjusted each of the four variable capacitors, one at a time, while monitoring the IC-R20 S-meter. With the capacitors adjusted for maximum and null signal strengths, I checked the VSWR on each band using the RigExpert AA600.

Satisfied with the results I conducted an on air test while monitoring the duplexer input VSWR using a Diamond SX40C meter, perfect!

2m/70cm duplexer. Fine tuning to a 50 ohm impedance match on 144.150 and 435.150 MHz.

When I’m not using the duplexer to drive transverters, it will be handy for SOTA activations on 2m 144.2 MHz SSB and 70cm 432.2 MHz SSB.

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