This reflectometer or standing-wave ratio meter (SWR) was found in a 1980s American documentation. The diodes support general purpose equivalents.
This simple metronome, from 1985 documentation uses only transistors and has two settings. For...
We found this circuit in a 1988 documentation. The circuit uses a conventional complementary...
This circuit was found in a 1990 publication. The sensors are electrodes placed in the water tank...