so ive been messing around with this for a few weeks now and i finally have something that kind of works but im not sure if im making it way harder than it needs to be. basically i have 4 antennas on the roof — a yagi for 2m, a dipole for 40m, a vertical for 20m/15m/10m, and a random wire i use for 80m on nights when conditions are weird. switching between them manually was driving me nuts especially during contests when im jumping bands every few minutes.

so i grabbed an arduino mega i had sitting in a drawer from an old project and wired it up to a bank of relay modules, the 8-channel 5v ones you can get off amazon for like 8 bucks. the idea is to have it talk to the PC over serial and the logging software sends a band change command and the arduino switches the right relay. ive got the basic serial parsing working and the relays click when i send the right bytes but im running into issues with the relay coils causing noise on receive. like i can hear it in the audio when a relay switches, little click or sometimes a buzz if the relay is chattering.

i put some flyback diodes on the coil pins which helped a little but its still there. wondering if anyone has done something similar and whether i put the relay board too close to the rig or if its an RFI thing getting into the audio chain. the arduino and relay board are sitting about 18 inches from the IC-7300 right now. also the ground wiring is kind of a mess at the moment if im being honest.

yeah the relay boards from amazon are basically fine for the switching part but the problem is usually the shared ground between the arduino side and the coil side. those cheap 8-channel boards technically have optoisolation but a lot of them the isolation is pretty garbage in practice, the ground planes are still connected through the pcb if you look closely. what you want to do is actually cut the trace or use the JD-VCC jumper if your board has one and power the relay coil side from a separate supply — not from the arduino's 5v rail. that alone usually cleans up a lot of the noise.

also 18 inches from the 7300 is probably too close. i keep my whole automation box in a separate enclosure on a shelf below the desk, like 3 feet away, and run shielded cable to the antenna switch. even then i had to add ferrite chokes on the serial USB cable before the clicking went away completely. the USB cable acts like a little antenna and just dumps the switching transients right into the PC audio chain which then gets into your rig through the sound card interface if youre using one of those.

not overkill at all, ive seen guys do way more complicated stuff for less reason lol. i built something similar but i went with a raspberry pi zero W instead of arduino because i wanted it to be network accessible so i can switch antennas from the shack PC or from my phone if im out back doing something. runs a tiny flask server, nothing fancy, just a webpage with buttons that toggle GPIOs. the pi drives a ULN2003 darlington array to actually switch the relays because you dont want to sink relay coil current directly through the GPIO pins, they cant really handle it reliably.

the noise thing is real though. took me a while to track mine down and it ended up being the 5v wall wart i was using for the whole setup was just noisy as heck. switched to a proper linear regulated supply and most of the interference went away. cheap switchers are terrible near radio gear, learned that the hard way.