Before there were fancy electronics to do band switching, or even to do simple things, the Diplexer (two ranges) and Triplexer (three) were a way to switch antennas for a transceiver.

This I claim no originality for, as I found it on the internet from the AmateurRadioMalaysia web site.

The original device was built into a die cast box, or similar using point to point wiring etc.

My take on the Triplexer was to see if a PCB could be used to achieve the same result but making it a bit easier to build. Eventually will also be in a die cast box.

Schematic is here (pdf file)

The original article gave no actual sweeps or what could be expected, so I am flying blind a bit here, but achieved suppression between the <=6m, 2m and 70cm bands in excess of 45db. See below. It also used ceramic trimmers but I had nothing in my junk box, so used film types. Since the IC-705 is only 10W (on 13.8v) hopefully they are sufficient. Long term stability may also be a problem.

This is my PCB. Note the intention is to fit this PCB into a small die cast box with suitable Co-ax connectors for the various ports.

The PCB is 50x100mm in size.

The original article used an SWR bridge to tune the sections, which would be very tedious. I used a spectrum analyzer with tracking generator which works well.

These are my plots: The 1st two insertion losses would be a little less if I had normalized the SA (ie remove cable losses) The last one is normalized.

HF arm, attenuation of 2M & 70cm > 50dB

NOTE, tuning of the Triplexer is highly dependant on impedance of the arms not being tuned. In the real world with real antenna, this may case tuning to be compromised.

2m plot. HF, VHF attenuation > 50dB

70cm arm, out of band attenuation >45dB

NOTE, the projects on these pages are presented in good faith.

They may or may not work for you.

Any damage to your ICOM IC-705 is not my responsibility as I have no control on what you may or may not do.

VK3PE (QRZ.COM for email)

Originally created by vk3pe on Jan 26th 2025