This small size radio published is very interesting and useful for students. Using the circuit describe here one can make very compact MW radio receiver. This circuit of radio receiver use only two transistor and few passive components only. As all the components can be easily placed in a small match box size cabinet.
Circuit Description of Match Box Size Radio
Coil L1 consist of 100 turns of 40 SWG insulated wire. Wind L2 over L1 which is 10 turns of the same wire. For L3 wind 56 SWG (approx) over ordinary IFT former without using core and metal cover. Counting of turns is not necessary. Wind the wire completed over former pulley. It may be fixed on the PCB using wax.
After making all connection, switch on SW1 and plug the earphone to your ear. Now rotate the gang’s knob slowly till you can hear programmer from the local Mw station. This circuit does not need an aerial. Playing of the unit near mains wiring is also not necessary. If clear result is not obtained check the connection once again. If they are alright adjust antenna coil over ferrite rod. This circuit will work very well with miniature speaker also.
Resistor (all ¼-watt, ± 5% Carbon)
R1 = 56 KΩ
R2 = 680 Ω
R3 = 10 KΩ
C1, C3 = 0.0047 µF
C2 = 220 Pf
C4 = 10 µF/16V
C5 = 0.01 µF
C6 = ½ 2* Gang capacitor
D1 = 1N34/OA79
D2 = 1N34
T1 = BF194
T2 = BC148
L1 = 100 Turns of 42 SWG over ferrite
L2 = 10 Turns of 42 SWG over L1
L3 = Wound 56 SWG thin insulated wire uniformly over IFT centre coil
SW1 = ON-Off Switch
B1 = 1.5V Battery