Indicator of radio signal
The goal of this project is to demonstrate what could be called an indicator or alarm radio signal. When tuned to a frequency that has a strong radio signal, the lamp lights. In the absence of a signal, the lamp turns off.
This circuit can be used as an alarm to a radio signal to a transmission failure that closes the position. Or, it can be used to monitor the frequency of the radio station which starts transmitting the morning at the time you want to wake up.
The receiver section of the project is similar to others we have described elsewhere. The transistor which drives the relay and the relay circuit are also described elsewhere.
To check if the operation is convenient, you can connect the listener through a coil or the other transformer. You will hear the radio and can then use this audible feedback to improve the tuning, the antenna connections (long antennas work best with 100 pF and 10 pF with short) and grounding connections. We've included some suggestions about antenna connections in different projects on radios and receivers.