SINGLE TRANSISTOR FM RADIO(easy home made) ~ what is electronics

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We often see simple circuits of AM radios but we rarely Find FM radio receiver circuits.this is one such rare circuit but a genuine one.

This is a simple FM radio circuit which enables you to listen FM stations near by ur surroundings,the circuit is very simple uses only a single transistor one can build this very easily.this constitutes very less number of components .this is a cost effective and compact circuit and easy to carry in journeys.the output of circuit can drive a hearphones.

WINDING L1

L1 sets the frequency of the radio, acts as the antenna, and is the primary adjustment for super-regeneration. Although it has many important jobs, it is easy to construct. Get any cylindrical object that is just under 1/2 inch (13 mm) in diameter. I used a thick pencil from my son's grade school class, but a magic marker or large drill bit work just fine. #20 bare solid wire works the best, but any wire that holds its shape will do. Wind 6 turns tightly, side-by-side, on the cylinder, then slip the wire off. Spread the windings apart from each other so the whole coil is just under an inch (2.5 cm) long. Find the midpoint and solder a small wire for C2 there. Mount the ends of the wire on your circuit board keeping some clearance between the coil and the circuit board.

A TUNING KNOB FOR C3

C3 does not come with a knob and I have not found a source. A knob is important to keep your hand away from the capacitor and coil when you tune in stations. The solution is to use a #4 nylon screw. Twist the nylon screw into the threads of the C3 tuning handle. The #4 screw is the wrong thread pitch and will jam (bind) in the threads. This is what you want to happen. Tighten the screw just enough so it stays put as you tune the capacitor. The resulting arrangement works quite well.

ADJUSTMENT

If the radio is wired correctly, there are three possible things you can hear when you turn it on: 1) a radio station, 2) a rushing noise, 3) a squeal, and 4) nothing. If you got a radio station, you are in good shape. Use another FM radio to see where you are on the FM band. You can change the tuning range of C3 by squeezing L1 or change C1. If you hear a rushing noise, you will probably be able to tune in a station. Try the tuning control and see what you get. If you hear a squeal or hear nothing, then the circuit is oscillating too little or too much. Try spreading or compressing L1. Double check your connections. If you don't make any progress, then you need to change R4. Replace R4 with a 20K or larger potentiometer (up to 50K). A trimmer potentiometer is best. Adjust R4 until you can reliably tune in stations. Once the circuit is working, you can remove the potentiometer, measure its value, and replace it with a fixed resistor. Some people might want to build the set from the start with a trimmer potentiometer in place (e.g., Mouser 569-72PM-25K).

SUBSTITUTES FOR OTHER COMPONENTS

Many of the parts are fairly common and might already be in your junk box. Only certain component values are critical. The RF choke should be in the range of 20 to 30 uh, although values from15 to 40 uh might work. The tuning capacitor value is not critical, but if you use values below 50 pf you should reduce or remove C1. The circuit is designed for the high impedance type earphone. Normal earphones can be used, but the battery drain is much greater and the circuit must be changed. To use normal earphones, change R3 to 180 ohms. Q1 can be replace with any high-frequency N-channel JFET transistor, but only the 2N4416, 2N4416A, and J310 have been tested. A MPF102 probably will work. C2 is not too critical; any value from 18 to 27 pf will work. C7 is fairly critical. You can use a .005 or .0047 uf, but don't change it much more than that.

PRECAUTIONS:

Unless you have experience with super-regenerative radios, I highly recommend using the FAR Circuits printed circuit board.
Connect the two sections of the variable capacitor (C3) in series to linearize the tuning somewhat. That is, use the connections on either end of C3 and don't use the middle lead.
L2, the RF choke should not be near a ground. The same is true for L1. Capacitance to ground will disturb the feedback.
The gain is just enough to drive an earphone. If you live too far away from radio stations, you might have trouble hearing one. There is no option here for an external antenna (that would require and extra transistor).
You can drive a speaker if you add an external audio amplifier.

If you want a little more audio gain, or you cannot locate a TL431CLP chip, you can use some other audio amplifier in the circuit where pins 1 and 2 of D1 normally connect. You can use an LM386 or a TDA7052 audio amplifier.

Part designator	Part description	Vendor stock number
C1a,C1b	10 pf, 50 v, ceramic disc capacitor	140-50N5-100J
C2	22 pf, 50 v, ceramic disc capacitor	140-50N5-220J
C3	RF tuning capacitor	N14VCRF10-280P
C4	330 pf, 50 v, ceramic disc capacitor	140-50P2-331K
C5,C8	0.001 uf, 50 v, ceramic disc capacitor	140-50P2-102K
C6	0.22 uf, 50 v, film capacitor	140-PF1H224K
C7	0.0047 uf, 50 v, ceramic disc capacitor	140-50P5-472K
C9	22 uf, 16 v, electrolytic capacitor	140-XRL16V22
D1	TL431AIZ voltage control Zener (shunt regulator)	511-TL431AIZ
EPH1	High impedance earphone	25CR060
L2	22 uh RF choke	542-70F225
Q1	2N4416A JFET transistor	510-2N4416A
R1	470K, 1/4 w, resistor	291-470K
R2, R3	1K, 1/4 w, resistor	291-1K
R4	10K, 1/4 w, resistor	291-10K
R5	1M, 1/4 w, resistor	291-1M
R6	100 ohm, 1/4 w, resistor	291-100
S1	Small SPST switch	10SP003
screws for C3	screws for mounting C3 (2 needed)	48SS03
nylon screw	#4 nylon screw used for tuning C3	561-T0440037
battery connector	mini battery snap	12BC025