Those are both extreme overkill for the task but participating in ADSB networks for sites like flightradar.

I really enjoyed making antennas and capturing data from satellites.

Getting trunking receivers (eg unitrunker) to listen to local first responder radio.

Decoding pagers is fun

As others have said, decoding various devices that talk on the various ISM bands is interesting.

Just band surfing at night is a lot of fun imho. Finding random signals and trying to figure out what they are is cool.