Software defined radio is great stuff. I've been helping a friend on the other side of the technology curve, he's been repairing things since the 1950s, and we'

Software defined radio is great stuff. I've been helping a friend on the other side of the technology curve, he's been repairing things since the 1950s, and we've done a ton of Tube and early transistor stuff... 100 pound boat anchors can be replaced with functionally superior boxes the size of a large USB stick. GNU radio is open source, and will work with your audio ports... so you can shift audio up/down in frequency, make a sonar, etc... all for free, and in your spare time. Add in a $30 RLTSDR dongle, and you can receive almost anything.