Quite often I get asked how simple can you make a receiver that gives useful results.
Of course the simplest of all is a crystal set that does not even need a battery.
The simplest circuit that really works well is probably the one shown. I even adapted this into a 1 FET 80m transceiver. The RX works well on AM, SSB and CW. By changing the tuned circuit, it will work on different bands. As a transceiver my main issue was netting the RX onto the TX frequency.
There are plenty of similar circuits on the Internet.
See https://sites.google.com/view/g3xbm4/home/hf-mf-and-lf/homebrew/80m-or-40m-regen-rx .
