This circuit for the 1750 m band was published in the September 1989 Radio Electronics magazine. The range depends on the antenna system and receiver used.
This circuit can use a pendulum sensor. We found this configuration in a 1994 publication. The...
This circuit is from a 1964 Electronic Design. The sensor is an LDR and the transistors are...
This circuit works both as a preamplifier and activates a relay when speaking in front of the...