Simple FM Radio (Updated)

Simple and powerful fm radio with easy to find parts

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.

Building

Radio is very sensitive and selective.

You may use any kind of Earphones. No high empedance earphones or crystal earphones needed.

C1 is 15- 80 or 20-140 pf variable Capacitor.

Transistor 1, is critical and it must be 2N3904

L1 is 1mm wire 12 turns in 8mm diameter. Other parts are not critical.

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 3.7-4.5 v. 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

4- Try different legs of Variable capacitor (in left in picture).

5- Antenna size is important. Try 15 cm to 1meter different lenghts.

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.

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.

Loudspeaker Version Without Germanium Diode

in this circuit first transistor must be 2N3904. Other general purpose NPN transistors wont work.

Also Antenna size is critical. Long antenna (or even antenna) can block tank circuit. You can find correct frequency range by varying coil turns and antenna size.

Radio circuits need some patience and lots of try to find your optimum circuit.

L1 Coil Winding counts also depends your Variable Capacitor. C1 is good between 20pf-170 pf.

Mini plastic Capacitors will be good for our purpose.

Zener circuit added for voltage stability. Otherwise frequency goes down when battery downs.

PAM8403 is a useful 5V Ampfi module but it can work good with 1S(3.7V) Li-ion battery.

Reccommendation

After getting work that circuit, its recommended to make soldered version. Its much more stabile. HF devices not properly working on Breadboards.