This circuit was found in an English publication from the 70s, an article that teaches how to calculate instruments. The circuit is still current and can be built with an analog indicator of 100 uA.
This small signal-following amplifier uses an integrated one that is not very common nowadays. Powered...
The resonant circuit depends on the crystal frequency that can go up to a few megahertz. The...
This direct conversion receiver circuit was found in Radio Electronics from the 90s. The...