AM radio transmitter

The AM radio transmitter does not use any modulator transformer. The audio output from condenser MIC is preamplified by transistor T3 (BC548). The audio output from T3 is further amplified by transistor T2 (BD139), which modulates the RF amplifier built around transistor T1 by varying the current through it in accordance with the audio signal’s amplitude. RFC1 is used to block the carrier RF signal from transistor T2 and the power supply.For antenna, one can use a 0.5m long telescopic aerial.  Details of RF choke, inductor L1 and coupling transformer:

• RFC1 = 30 turns of 24 SWG copper wire on 6 mm diam, air core
• X1 (transformer) = 15 turns primary, 3 turns secondary using an IFT core with tuning slug
• L1 = 4 turns of 22 SWG copper wire on 15 mm diam air core