Low current indicator (CB22147E)

We found this circuit in an old English documentation. The idea is a momentary indicator that flashes only when the circuit is turned on.

Antenna tuner (CB6982E)
This circuit for receiving or transmitting low power was found in old American documentation. It is...
Noise canceler (CB8774E)
Suggested by the 90s ARRL Handbook edition, this circuit aims to reduce or cancel noise at the...
Adapted from capacitance (CB25301E)
This circuit allows you to read capacitances on a common analog instrument. It is part of an...