The CTR2-Mini Antenna Switch Controller is available in two versions.

The 1X version shown in the lead photo allows you to control an external antenna switch with 1 radio port and up to 8 antenna relays. The relays on this version are not interlocked and they can be selected in any sequence. This is useful if you need to select multiple elements of a phased array antenna system.

The 2X version allows you to control an external antenna switch with 2 radio ports and 4 or 8 antenna relays on each radio port. The relays in this version are interlocked so it is impossible to select the same antenna for both radio ports. While you can select multiple relays, they must be for the same radio port.

Here’s a photo of the 2X4 version. Note that there is one LED for the A and the B radios on each relay port.

The Bill-of-Material (BOM) is the same for either switch version. The only difference is in the PCB and schematics for the two versions. The schematics and build instructions for the CTR2-Mini Antenna Switch Controller can be found below. There are links on the BOM spreadsheet to locate parts on You can use the part #s to find these parts at other part suppliers. Click the Download PDF button to download the file.

Bill of Material

NOTE: The SMT components marked Included on PCB on the spreadsheet are pre-installed on the PCB. You do not need to order these parts.

Mouser BOM

I have also created an automated BOM on for this project. This allows you to easily order the through-hole components and a Wio Terminal to build the antenna switch controller. You can order the PCB (with all SMT components pre-installed) and the optional enclosure kit on my CTR2-Mini order page. The PCB kit comes with the main board and the Wio GPIO Interface board. The enclosure kit includes the pre-assembled acrylic stand shown in the lead photo plus a 1.3″ black knob, four push button switches and five DuPont jumpers for the function keys, the board mounting hardware, and four silicone rubber feet.

Mouser: CTR2-Mini Antenna Switch Controller

Interactive BOM

I’ve also created interactive BOMs for the 1X and 2X versions of the board. These are very helpful when assembling this project. Just unzip the HTML file and open it in your browser. It also gives you a good idea of what needs to be done to build the ASC. Just select the Front View.


The schematic for each antenna switch controller version can be downloaded below.


Construction of the antenna switch controller is pretty easy. Only the through-hole components on the top of the board need to be installed. You should be comfortable soldering header pins on .1″ centers. All the SMT components are pre-installed on the bottom of the PCB so no worries there.

Populating the Main PCB

The main PCB is supplied with all SMT components pre-installed at the factory. You only need to install the through-hole connectors. These can be installed in any order. Download the interactive BOM file for your board above and use the front panel to guide you.

There are a couple of things to be aware of when building the board.

  1. You don’t need to purchase and install the Expansion connector (J2) on the 2X board if you’re not planning on adding an expansion board. You can always buy it and install it if you decide to install the expansion board in the future. (The expansion board allows you to control 8 relays on each radio port on a 2X board).
  2. You don’t need to purchase and install the Remote Encoder connector (J3) if you install the encoder/function button board.
  3. You don’t need to purchase and install the MOVs (RV1 through RV8) if your remote antenna switch will be mounted close to the ASC.
  4. You can use either EC2-5TNU (5 volt) or EC2-12TNU (12 volt) latching relays (if you can find them). JP3 sets the power source for these relays. By default JP3:1-2 is closed for 5 volt operation. If you use 12 volt relays, open JP3:1-2 and solder across JP3:2-3. I’ve found the 12 volt relays are nearly impossible to find.
    NOTE: Power to the external antenna switch relays is always 12 volts. JP1 and JP2 determine if it’s positive or negative sourced.

LED Placement

The LEDs should be installed with the long lead inserted in the square pad. Since they are bi-directional this will insure they are all the same color.

The 2X PCB is laid out so that the A LEDs are one color (red) and the B LEDs are the opposite color (yellow). This helps distinguish the active antenna relay for each port.

Solder one lead of the LED first then check for alignment. It is much easier to adjust the alignment with only one lead soldered!

Encoder/Function Button Board

The Encoder and Function Buttons mount to the top panel of the enclosure as shown in the photo. To build this board:

  1. Install the four supplied pushbuttons on the acrylic top panel with their terminals facing front to back as shown below.
  2. Install an 8-position right-angle .1″ header on the bottom of the encoder PCB. This is where the DuPont jumper wires connect as shown below.
  3. Solder the encoder to the encoder/button PCB with the F1, F2, F3, F4 labels facing up.
  4. Mount the encoder and the PCB to the acrylic top panel using the supplied nut and washer for the encoder.
  5. Solder small jumper wires from the terminals of each switch to the pads on the PCB. I’ve found it easier to put a small blob of solder on the pad then push a wire with a 1/16″ ‘L’ bend on one end through the hole in the button’s terminal and solder the ‘L’ bend end to the pad on the board.
  6. Solder the other end of the wire to the terminal and clip the excess wire. Do this for all eight switch terminals.

NOTE: If you need to remove the encoder/button board in the future just unscrew the nuts on the encoder and pushbuttons and remove the entire assembly.

Power Options

There are several power options on the controller.

  1. Connect an external switch to JP4. The BOM has a rocker switch that fits the acrylic enclosure that I can provide. You can use any switch you want for your enclosure or you can install a jumper here to keep the ASC powered on all the time. You can use the Wio’s power switch to turn it off.
  2. Power to the external antenna switch:
    • Strap JP5: 1-2 to provide power to the external antenna switch when the ASC is turned off (it has latching relays). This will keep your antennas active all the time.
    • Strap JP5: 2-3 to provide switched power to the external antenna switch. Your external switch will go offline when you turn the ASC’s power off.
  3. Power Polarity to the external antenna switch:
    1. Strap JP1 and JP2 1-2 to provide +12 VDC to each control lead to the external antenna switch. Ground (return) is supplied on pin 9 of the DB9 connector. In this mode all of the LEDs on the 1X switch and the ‘A’ LEDs on the 2X switch will all be red. The ‘B’ LEDs on the 2X switch will be yellow.
    2. Strap JP1 and JP2 2-3 to provide Ground to each control lead to the external antenna switch. +12 VDC (return) is supplied on pin 9 of the DB9 connector. The LED colors will be reversed in this mode. If you want the LED colors to match the display colors in this mode, install the LEDs with the short pin in the square pad.

Wio Terminal GPIO Board

The Wio Terminal GPIO board connects the ribbon cable from the main board to the Wio Terminal. To build this board install the 2×20 .1″ header on one side of the board and the 16-pin ribbon cable connector to the other side as shown below.

Ribbon Cable

Build a 16-conductor ribbon cable to connect the Wio Terminal connector on the main board to the Wio GPIO board. Cut the ribbon cable to be 120mm long. Total length should be 100mm after the connectors are installed. Pay special attention to the direction of the connectors as shown in the photo below.

External Antenna Switch Wiring

A female DB9 connector is installed on the ASC to connect to your external antenna switch. You can use a standard RS232 serial cable to connect to your switch if it’s close to the ASC. Just cut off the far end and hard wire it to the terminal strip on your switch. If your switch is mounted some distance from your shack you can use a DB9 breakout box such as this one on Amazon to connect the ASC to shielded 9 conductor cable.

  • On the 1X version of the ASC pins 1 to 8 wire directly to relays 1 to 8 on your remote antenna switch. Pin 9 is the common.
  • On the 2X version of the ASC:
    • On the main board, pins 1 to 4 wire to relays A1 to A4 and pins 5 to 8 wire to relays B1 to B4 on your dual port antenna switch.
    • On the expansion board, pins 1 to 4 wire to relays A5 to A8 and pins 5 to 8 wire to relays B5 to B8 on your dual port antenna switch.
    • Pin 9 on both DB9 connectors is the common.
    • NOTE: You must strap the switch polarity (JP1 and JP2) the same on the main and expansion boards!

Expansion Board

Two control boards are required to control a dual-port 8 antenna (2×8) external switch. One board will be the main controller and the other will be the expansion controller.

Build the main controller as shown on the 2X schematic. Populate J2 and J4 with 16-pin ribbon connectors.

On the expansion board:

  1. Cut JP6: 1-2 and JP7: 1-2 (PCB pads). Make sure they are open.
  2. Solder bridge JP6: 2-3 and JP7: 2-3
  3. Install a jumper on JP5:2-3
  4. Install only the J2 16-pin ribbon connector on the expansion board
  5. Build a 16-conductor ribbon cable using a 60mm piece of ribbon cable (total length with connectors should be 40mm). This cable connects J2 on the main board to J2 on the expansion board.

Connect the DB9 connector on each board to your external antenna switch as follows:

  • Main DB9 Pins 1 to 4: Connect to relays A1 to A4
  • Main DB9 Pins 5 to 8: Connect to relays B1 to B4
  • Expansion DB9 Pins 1 to 4: Connect to relays A5 to A8
  • Expansion DB9 Pins 5 to 8: Connect to relays B5 to B8
  • Connect Pin 9 on both DB9 connectors to the return on your external antenna switch.

I hope this project sparks some interest in building your own antenna switch controller. It’s pretty easy to build. As always, if you have any questions please contact me,

73, Lynn, KU7Q