Remote HF Antenna Switch
Design
I wanted a remote antenna switch, and commercial models seem to be expensive relative to what I am willing to spend. I planned to combine an Arduino, ethernet shield with power over ethernet, and a board with four relays. This assumes that commonly available relay boards would work fine for switching HF signals, providing both adequate isolation (separation when an antenna is turned off) and have minimal losses when in use. I had planned to add on remote control for an automatic antenna tuner and an antenna rotator, but those two features will be for some future iteration of the project. I have at least two HF antennas I wanted to connect, a short G5RV and a two element 6M beam.
Micrcontroller
After running into issues with a standard Arduino Uno and ethernet shield - there wasn't enough memory to serve up a minimal HTML page via HTTP to control the switch. I looked at some successful projects using networked Arduinos for remote control, like the OpenSprinkler, finding the source code was more optimized than I thought I could get for a one-off hobby project.
Next idea was to look at something like the Arduino Yún, which I discovered was unavailable at tthe time. I did find Adafruit selling a clone called the Seeeduino Cloud, marked as compatible with the Yún, and bought a Power over Ethernet (POE). I would not recommend the Seeeduino Cloud as it uses a custom branch of the OpenWRT Linux distribution that several years since having any kind of update, and minimal documentation. So I set up two parts - a static HTML page with JavaScript for interactivity, served up by the Seeeduino's Linux side, and used the Arduino YunBridge library with a REST API to turn the appropriate pins for each relay on and off. It works okay, but can be a bit buggy when the Arduino loses it's connection.
Relay board
I mounted a Sainsmart relay board and Seeeduino into an old project box I had bought years ago for a manual antenna switch and never implemented. I built a small RF sheild around the relay board using an old piece of aluminum bent to fit around it, and wired it up using some speaker wire and panel mount SO239 connectors
I had considered their relay board with a built-in web server, but this was out of stock at the time.
Testing
I can't tell if there is any isolation between these. I used a friend's NanoVNA to find minimal losses on each of the connectors when selected, but I cannot hear any difference between connectors on the radio with one antenna hooked up.
My next steps will be to rewire the relay board to directly solder to the PCB with short stubs of 14 gage copper wire to each connector and see if this works better.
Antenna Rotator?
My neighbor, another ham, gave me a TV antenna rotator and homebrew controller. The controller requires a five wire connection to the rotator, three for power and two to measure voltage across a potentiometer that indicates direction. I had planned to incorporate controlling the rotator into the initial project until I started to investiate how to provide power to it. The antenna rotator obviously requires more power to operate than I could deliver over PoE. The homebrew controller provides 40V AC from a substanial transformer connected 110V AC. The 40V AC appears to need to be reversed to rotate the controller in opposite directions, meaning four relays need to be used as a DPDT switch. By the time I configure this, I still need to provide at least three wires up to the rotator, plus the ethernet to the Seeeduino. I am not sure I'll complete this, instead I am planning to run 18 gauge, 7 conductor, sprinkler wire to the rotator.
Antenna Tuner?
Secondary to the antenna switch and rotator controller, I wanted to connect either my LDG Z100 autotuner or another autotuner to the Seeeduino. Locating the tuner near the antenna switch would allow me to minimize the impedance mismatch over the majority of my feedline, about 50ft from my shack to the mast on my garage. The controls for the LDG autotuner appear to be pretty minimal, using a four pin connector from my Icom radio, esentially power and ground, and two pins communicate when to tune and status of tuning. This should be easy to add at a future point.