Amateur radio and embedded systems

Coax relay PCB for HF antenna switching

This is a simple board that switches 4 antennas to a single transceiver. It features SO-239 coax connectors, relays with popular footprints and flyback diodes. Unused antennas are grounded. It can be driven by virtually any controller in the shack. This design is soooo good that it got copied on Aliexpress! 😁

PCB top view

How to get one?

Gerber files are available here. ←

You can get them manufactured for example at Makerfabs for $0.5 each, or Elecrow, or any other PCB house. The PCB is two-layer, 90 x 90 mm, any surface finish will do.


  • the PCB
  • 5 x SO-239 connectors: the rectangular, panel-mounted flavor
  • 4 x relay with 12V coil: Schrack 6-1393243-3, Relpol RM-84, or similar
  • 4 x diode: any will do, for example 1N4001 (but not 1N4148!)
  • BS23 enclosure or similar
  • random screws and washers

Remote QTH markets a similar switch with the same Schrack relays and says that they can handle up to 2.5 kW.

PCB bottom view


I recommend starting with soldering down the relays, then mounting the diodes at the bottom side. The diodes can be semi-surface-mounted (see pictures).

Depending on which wiring and controller you have the relays can be operated with a common positive supply (easy to drive with an ULN2003) or a common negative by adjusting which way the diodes are mounted.

Further steps depend on the exact enclosure. A similar assembly can be found here. Typically, soldering of the SO-239 center pins must come last.

Example builds made by SQ2RBY

SQ2RBY build top view

SQ2RBY build bottom view

SQ2RBY build top view in enclosure

SQ2RBY build enclosure bottom view

SQ2RBY build 1

SQ2RBY build 2

SQ2RBY build 3

SQ2RBY build 4