27 or 49 Mhz frequencies have different channels for toy RC controls. One example, 27.145 (channel 4, or yellow). Hobbyists with FCC licenses can use other frequencies. Different countries may use different frequencies.
Using good transmitter batteries, set this field strength meter a few feet away and touch up transmitter for maximum field strength output.
Adjustable 10 K resistor is to set low current meter sensitivity. Diodes are Si/Ge materials.
16 ohm resistor is to use earphone in place of meter. Remove meter and connect top wire to earphone resistor. Modulation that could be heard on earphone would be needed. Short antenna at top left to pick up signal.
