Small FM radio receiver
This circuit is FM radio receiver that very small size and works well, although the sensitivity is poor. The principle of this circuit is to use the generator frequency circuit. Which consists of Q2 and Q3, they work by producing a frequency sync with the frequency has been derived. By the Q1 which acts as a pre-amp extension of the frequency VHF range wider. We may cut the Q1 out, then connect the antenna at the C4, but the sensitivity of this circuit will decrease.
We can adjust the C5 in the frequency generator circuit. To control the frequency from 87MHz to 108 MHz. And the frequency of the incoming sync with the frequency of the generator itself. Therefore, the frequency deviation of the signal received from the antenna to the audio signal. By the frequency modulation is across the VR1 + R5. the low pass filter circuit, R6/C6 be the frequency of sound, then after be amplified by the Q4 and Q6, and is enter to output by C9 respectively.
Details are as follows: Coil.
L1 is 10 turns of 25 SWG enamel coated copper wire wound with a inside diameter of about 3 mm, The L2 is 13 turns of 25 SWG inside diameter of about 3 mm, L3 is 4 turns of 18 SWG inside diameter of about 5 mm.