The CTR2 RJ45 Switch is a modular design to allow you to build only what you need for your station. Four boards are required to complete the entire 16-port switch but you can add them one at a time as your needs changes.

The design defines the first board as the master. It contains the decoding logic and voltage regulator in addition to the connectors and relays. It is always required and always controls Radio I/O ports 1 through 4. The expansion boards only required the connectors and relays. They are controlled by the decoding logic on the master board. Their port range is determined by the expansion port their Expansion Port (J3) is plugged into. See this post for a full explanation of this board.

All RJ45 switch boards are built with the same PCB. The only difference is which parts are populated on each board. All PCBs are supplied with SMT components installed. The builder only needs to install the through-hole components as shown on the bill-of-material list.


On the master board, all through-hole components except J3, Expansion Port, need to be populated. If you don’t plan on using any expansion boards you can leave off expansion connections J4, J5, and J6. You can always add them in the future when you’re ready to expand. If you only need two or three ports you can leave off the relay groups you don’t need and add them later as your needs changes.


The expansion boards only need the 4-port RJ45 connector, 16 relays, Radio I/O connector (J2), Radio Expansion connector (J3), and LED’s D1 through D4. The LED current limiting resistors and RF filtering ferrites and caps are pre-installed on the board. As with the master board, you only need to install the relay groups you need.


As with any electronics construction project, take your time. Make sure you have a well lit area to work in, a fine-tip temperature controlled soldering iron, solder, a tip cleaning pad, and solder wick. A circuit board vise is handy to hold the board in place while you build it. I use this one because it’s inexpensive and does a good job. Feel free to buy one that fits your needs.

Purchase the components you need from the bill-of-material list before hand so you can build the board in one evening. The relay and ribbon connector pins are small on closely packed so make sure there are no solder bridges between them. If you do create a bridge use soldering wick to remove it. Also, be careful not to overheat the 10-pin ribbon connectors. It’s easy to melt the pins out of alignment.

Speaking of the 10-pin ribbon connectors. They are marked so you know where pin 1 is located. Make sure this matches up with the #1 pad on the board. The #1 pad is square where the others are round. The connector has a small triangle marking the #1 pin as shown in this photo.

I find it’s easier to install the relays first then add the connectors.


Once you’ve finished the board you’ll need to build the ribbon cables to connect them together. I have an entire blog post on building ribbon cables here. The main thing to remember is to cut the ribbon cable square so it aligns in the connector properly and make sure everything looks good before squeezing them together. Buy extra cable and connectors because you’ll probably need them (I did). Be extra careful measuring and building the multi-tap cable for the Radio I/O bus. There should be a minimum of 40mm between each connector to fit the boards on 25mm standoffs.

When building the multi-tap cable for the Radio I/O bus, stack the boards using 25mm standoffs and carefully measure each connector’s location on the cable allowing extra for the strain-relief fold-back. A little extra length won’t hurt anything. The extra length can be fit between the boards on each level.

The drawing below shows the ribbon cables required for a full 16-port switch.