Hi all,

Kindly explain the attached circuit diagram.

Thanks in advance

 

Which one, you included two of them?

The first is a basic RF oscillator/transmitter. Basic common base configurations, the cap between the collector/emitter is for feedback, and the collector tank circuit selects the frequency.

 

Circuit 2 is an alarm. If AC power is present, T3 will be on and energize the relay, opening the alarm contacts. If T2 gets turned on, it will pull T3 out of conduction, and sound the alarm.

It is not clear to me under what conditions T2 will turn on.