so ive been messing around with this idea for a few months now and finally started building it out. basically i have four antennas out back — a 40m dipole, a vertical for 20/15/10, a loop, and a discone for the scanner stuff — and im sick of going out to the junction box every time i want to switch. its out past the garage and in winter its just not happening.

i picked up an arduino mega i had sitting around from an old robotics thing my kid did and figured i could use a relay board to do the switching. got one of those 8-channel 5v relay modules off amazon for like $8 which seems almost too cheap to trust honestly. the plan is to run it over serial from the shack PC and either write a little python script or maybe tie it into hamlib somehow.

has anyone actually done something like this? im curious if the relay switching causes any RFI issues, the cheap relay boards scare me a little for that reason. also wondering if a pi would be better than the arduino for this since i could run a little web interface from it and control it from my phone without having to have the shack PC on.

yeah i did almost exactly this about two years ago, ran into the same questions. the cheap relay boards are fine electrically but you might want to pot them or at least keep the arduino physically away from the RF path. mine caused zero interference but i also have the control box mounted outside next to the switch box and the arduino is inside a grounded metal enclosure i cobbled together from an old project box. the serial run to the shack is cat5 which works fine.

as for pi vs arduino — honestly i ended up moving to a pi zero W for exactly the reason you said, the web interface thing is really useful especially when youre in the middle of a pileup and dont want to mess with anything else. flask makes it stupid easy to throw together a basic antenna selector page. i can pull it up on my phone or any browser in the house. only real downside is the pi takes 30 seconds to boot if power gets interrupted, arduino is instant on which matters if you have a UPS situation or something.

one thing i wish i had done from the start is put some coax relays in there instead of just switching the feedline grounds with the relay board logic. depends on your power level though, if youre running barefoot or low power the module relays are probably fine.

those 8 channel relay boards work but watch out for the optocoupler input logic, some of them are active low which trips people up. i fried one relay trying to figure out why my logic was backwards lol. just check the datasheet for whatever board you get before you assume high = on.