About This Project
These switch kits are the output from an effort to keep myself busy while on COVID-19 lockdown. I originally intended to just teach myself how to program and interface with various types of microcontrollers (PIC, Arduino, etc.). So, I bought several of the newbie training kits off of eBay and went to town. After exhausting all the built-in exercises, I went looking for a project where I could use my new-found knowledge.
I had owned an Ameritron RCS-12 remote antenna switch for many years and had always wondered how they selected antennas by simply pushing a momentary pushbutton switch. After opening up the controller, my suspicions were confirmed that a microcontroller was at the heart of the design. So, I decided to attempt to recreate the unit’s features that I used most as a breadboard project.
The Ameritron switch has many features that make it a popular remote automatic antenna switches on the market: it interfaces with most radios for automatic antenna selection based on band data, it has the ability to control most remote relay boxes besides their own, it has a transmit lockout safety feature, etc. I only needed to build one that had a few of these features:
- Band Data Interface with Yaesu and Icom Radios only – I only have radios from these manufacturers and the Kenwood radios don’t really provide separate band data and must be queried via their CAT interfaces which was beyond my ability at the time.
- 4-Conductor control line for the remote relay box – I had the control cable already pulled.
- Manual Antenna Selection by simply pressing a momentary pushbutton.
- Automatic Antenna Selection – With the ability to easily program the antenna buttons based on the currently selected HAM band.
- Transmit lockout – For safety purposes. You do NOT want to inadvertently change antennas while transmitting.
- Support full legal power output.
I got started by researching interface circuits for driving relays and LEDs as well as how to adequately buffer input signals and threw these together using simulation software. BTW – I highly recommend DesignSoft’s TINA for simulating circuits as it has support for most of the most common microcontrollers – including the ability to program the simulated MCUs. Next, I put everything on the breadboard and measured real-world voltages and currents to confirm what was predicted in the simulation software.
Once I had the switch actually working on the breadboard, I just couldn’t leave well enough alone. I decided to actually build a working model. This led to the need to learn some other skills such as circuit board design and manufacturing and the metalworking skills needed to modify stock enclosures. I went searching for circuit board design software and settled on EasyEDA simply because it had a huge following on the Internet. I was not disappointed. You can choose to add components from their partner parts vendor (LCSC), or you can add your own. Once added to the schematic, you can make all electrical connections very easily. Once the schematic is complete, you can seamlessly choose to create a circuit board. All the component footprints and silkscreen lettering are brought over from the schematic. All that is required is for you to arrange the components on the board then select the auto-route feature to have all the circuit board traces created (it’s a little more complicated than that, but you get the picture). From here, you can create the Gerber files needed to send to any number of low-cost circuit board manufacturers (EasyEDA has a direct link to a prototype circuit board manufacturer in China (JLCPCB) who I found to be very inexpensive as well as quick to turn around boards).
With shiny new circuit boards in hand, I quickly assembled the controller and remote switch box. After extensive testing to verify that the original design parameters were met, I began to realize that this could be assembled into a kit and sold to my fellow HAMs at the hamfests that I had been missing since the pandemic shut everything down – and I could use the proceeds to fund said trips.
So that is what I did. I hope you find that this remote antenna switch meets a need in your shack.
Now that things have begun to open up, I hope to meet in person at one of the upcoming mid-Atlantic hamfests in the near future.
Don – WA4MCM