so ive been messing around with an arduino mega for the past few weeks trying to get it to handle my antenna switching automatically based on band selection from my IC-7300. the radio puts out band data on the ACC port and i figured i could decode that and drive some relays to switch between my vertical, the 40m dipole, and the hex beam depending on what band i land on.

got most of it working actually but im running into a weird issue where the relay for 20m keeps chattering when i transmit. like it'll switch fine when im just tuning around but the moment i key up it starts cycling. i thought maybe RF was getting into the arduino somehow but ive got ferrite beads on all the data lines and even wrapped the relay board leads a couple times through a toroid. doesnt seem to help much.

also considered moving the whole thing to a raspberry pi zero instead just because i already have a few laying around and it would make logging easier down the road. not sure if thats overkill for just switching though. anyone gone down this road already

yeah the RF getting into the arduino is almost certainly your problem, ferrites help but they dont always solve it especially if your ground scheme is sloppy. what are you using to power the arduino? if its sharing a ground with anything connected to the radio that can cause all kinds of weirdness when you key up. i had the exact same chattering issue on a similar project and it turned out my USB power supply was doing something funky - switched to a dedicated 5v linear reg off a clean 12v source and it basically went away.

also worth adding a 100nf cap right across the relay coil if you havent already, that helps suppress the back EMF spike. might not be your main issue but it cant hurt.

on the pi question, i wouldnt bother for just switching. the boot time alone makes it annoying if you lose power, arduino is just way simpler for stuff like this. i use a pi 4 for my logging and cluster stuff but keep the control stuff on micros.

I did basically this exact project last year for my shack, different radio but same idea. One thing that helped me a lot was optoisolating everything between the arduino and the relay board, those cheap blue relay modules from amazon pull the coils low so the logic side is kind of floating and it can pick up RF. Get a proper isolated relay board or roll your own with optocouplers, made a huge difference for me.

Also just curious what you're using to decode the band data from the 7300, is it the CI-V or the actual band voltage outputs on the back? I ended up going CI-V over USB which meant the pi actually did make more sense in my case since i needed a serial stack anyway. Different tradeoff depending on how your radio outputs the info i guess.