This circuit allows converting an old AM MW tube radio that has the tubes indicated in the outgoing schematic on a small AM transmitter with a range that reaches 100 meters.
What is done is to add a switch that switches the audio output through an oscillator coil that generates the RF signal. The external modulation comes through C4 being a ceramic microphone or even a small amplifier with microphone.
The antenna consists of a piece of wire about 2 or 3 meters in length and L1 is made by winding 50 + 50 turns of 28 AWG wire in a 2.5 cm diameter PVC pipe or a piece of broom handle.
The variable (C1) can be obtained from an out-of-use AM tube radio and the capacitors have the following specifications:
C2 - 100 pF - ceramic
C3-10 nF - ceramic
C4 - 220 nF - ceramic
Figure 1 shows the complete diagram of the system.
The key is to bring the receiver back to the normal function.
