Simple and powerful fm radio with easy to find parts
Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: Circuit
This is a regenerative Fm radio. Build very simple and easy to find parts. No special coils or uhf transistors.
Antenna catches fm waves, first transistor works as oscillator. R1, L1 and C1 determinates oscillation frequency. Internal freq and cathed freq overlaps and gets more power. Germanium diode detects audio freq. T2 and T3 works as audio ampflifier. Last condansator connected to jack is 45uf electrolytic con.
Note: if Fm broadcasts are weak or far away in your area, please use v2 circuit in troubleshooting step! Thank you.
Step 2: Work
Radio is very sensitive and selective.
Parts values in circuit is critical for oscillation and biasing of transistors.
You may use any kind of earphones. No high empedance earphones or crystal earphones needed.
C1 is 80-140 pf variable condensator. Once tunning with C1, you can fine tune with P1. Other potentiometer P2 is for volume control.
Step 3: Troubleshooting
1- There is not any voice: check all connections and transistor legs must be correct position.
2- There is a "hush" but no radio signals: check your battery it must be about 6-9v. If everything ok but still no signal, genly compress coil from laterals or get wider by your two hands.
3- Radio signal is not stable: in best receiving, hot glue your coil to fix in stable condition
Also if there is too many elegtromagnetical pollution in your area, it may be necessary to faraday isolation for your tuner part. To obtain this, aliminium foil coated cardboard may be good idea. Or you may try 2st version of circuit above. If u realise this 2nd version take p1 and c1 to middle position, move p1 till hear fm hush then search channels with c1.
Step 4: Putting in a Case
I build soldered version. Buyed a fuse box from a n electric warehouse. This is a wall fusebox.
Tips: if u wanna make soldered version make circuit on a wide area. Also coil lenght is very important to obtain fm bandwidh.
Step 5: Whats Next?
Version 3.0 without variable capacitor. Tuning with only 10k potentiometer.
Will be here shortly.