When it comes to making an FM receiver it's always thought to be a complex design, however the one transistor simple FM receiver circuit explained here simply shows that it isn't the case after all. Here a single transistor acts as a receiver, demodulator, amplifier to constitute a wonderful tiny FM radio.
It's basically based on a superregenerative audion receiver circuit where the use of minimal components becomes the main feature of the unit.
However fewer components also means a few compromises involved, here the receiver requires a large metal base for grounding the unwanted signals, and for keeping the noise factor to the lowest, and also this system would work only in places where the reception is rather strong and thus may not be suitable in areas where the signal strength is thinner.
How the One Transistor FM Radio Receiver Works
As mentioned above, the circuit is basically a single transistor superregenerative RF oscillator with a constant amplitude.
Here we have tried to enhance the design such that the amplitude becomes considerably magnified in order to turn OFF the transistor completely during the oscillations.
This called for an increase in the feedback capacitor and also to use a transistor specifically designed for handling extreme high frequency ranges such as a BF494.
Further modifications include an inductor with the emitter of the transistor, and a capacitor across the emitter resistor of the transistor.
Due to this the transistor is switched ON as soon as the base emitter voltage of the transistor falls significantly, resulting in an abrupt cut off in the oscillations.
However this prompts the emitter capacitor to discharge, allowing the collector current to yet again resume its flow, initiating a fresh cycle of oscillation.
The above happening forces the circuit to flip flop between two situations, oscillator OFF and oscillator ON, resulting a sawtooth frequency of about 50kHz at the output.
Each time the circuit flips across the above ON/OFF states, results in a significant stepping up of the amplitude which in turn constitutes greater amplification of the received signals. The procedure also gives rise to noise but only as long as a station is not being detected.
The above design has one drawback, though. The output received from the above circuit would have greater content of sawtooth noise compared to the actual FM reception.
A smart technique can be seen employed in the following single transistor FM radio circuit to attribute better efficiency to this simple design.
Here we pull out the emitter capacitor C5 ground link and connect it with the output.
This results in a fall in the collector voltage as the collector current rises, which in turn forces the emitter voltage to rise, prompting the emitter capacitor to negate the situation at the output.
This enforcement results in making the sawtooth effect on the received signal practically to zero, thus presenting an FM audio with much reduced background noise.
Single Transistor Radio with Audio Amplifier
To make the above circuit self-contained, an additional transistor stage may be introduced for enabling the radio to play the music loudly over a small loudspeaker.
The circuit is self explanatory, just the inclusion of a general purpose BC559 transistor along with a few inexpensive passive components can be witnessed in the design.
How to Make the Inductors
The involved coils or the inductors are very simply to wind.
L1 which is the oscillator coil is an air cored inductor, meaning no core is required, wire is super enamelled type, 0.8mm in thickness, diameter of 8mm, with five turns.
L2 is wound over R6 itself using 0.2mm super enameled copper wire with 20 turns.
How to Set Up the Circuit
- Initially when the circuit is switched ON, the output will be accompanied with substantial background noise which will gradually tend to disappear on detection of am FM station.
- This may be done by carefully tuning C2 with the help of an insulated screwdriver.
- Try to keep the tuning at the edge of the band of the particular FM station, with some practice and patience this would get easier with time.
- Once tuned, the circuit would respond to that reception every time its switched without the need for further alignment.
- As indicated at the beginning of the article, the circuit should be installed over a wide circular meta plate, preferably a solderable material, and all the ground of the circuit soldered on this plate.
- This is important to keep the circuit stable and avoid drifting away of the received stations and also for cancelling unwanted noise.
- The antenna in the proposed single transistor FM radio receiver circuit is not crucial and in fact should be kept as small as possible, a 10cm wire would be just enough.
Remember, the circuit also acts a like an effective transmitter circuit, therefore keeping the antenna size bigger would mean transmitting noise across the ether and disturbing your neighbors radio reception.
The upside being that the design can also used as a walkie talkie within a small radial distance....more on this next time.
Smallest One Transistor FM Radio Receiver Circuit
Parts List
- C1 = 10 pf variable trimmer capacitor.
- D1 = 1N82 diode.
- L1 = 5 turns using No. 16 magnet wire wound on a 3/4 -inch diameter coil former, 1/2 inch long. It should be tapped at 1/2 turn from the ground side for connecting the antenna, and tapped 2 turns from top of coil for connecting the diode.
- T1 = BC547 transistor.
- R1 = 1K 1/4 watt 5% resistor.
- Earphone (magnetic)
This is a fascinating small single transistor FM receiver that, unbelievably, can tune the full 88-108 MHz FM music band while still producing enough energy to power a typical set of magnetic earbuds.
The tiny receiver is so small that it could be integrated into an empty cigarette pack. This tiny FM receiver can additionally catch the audio paths of some television channels.
How to Setup
The only challenging aspect is really the L/C circuit, that comprises of a 10-pf trimmer capacitor and a tapped antenna coil connected in parallel.
After completing L1 winding, test the circuit first. Try flipping the taps on the coil if you are having trouble hearing the FM stations.
If you're still having trouble, try experimenting a little with the coil by adjusting the taps a fraction of a turn at a time, individually, while attentively listening via the headphones and tweaking C1 with each adjustment you make.
Antenna Specifications
Just about any length of strong (whip-like) No. 10 or No. 12 wire could be used for the antenna. However we discovered that 3 and 1/8 inches worked best for the middle of the f-m band.
If the indicated 1N82 diode cannot be found, any other vhf diode could be used instead.
Other diodes like the OA91 work well at this frequency as well.
If magnetic earbuds are used, which we advise, simply remove R1 from the circuit.
Single IC Small FM Radio Circuit
If you are looking for an FM radio circuit which should be as small as possible yet have a very high accuracy in terms of band selection, then you can try the following concept.
It uses a single chip TDA7000 for the modulation and demodulation of the FM stations, and uses the IC LM386 for amplifying the captured audio signals.
Everything in this single chip FM radio circuit looks straightforward except the two inductors. The two inductors L1 and L2 can be built in the following manner.
Both the coils have 100 turns and uses 28 SWG super enameled copper wire. Coil L1 has a center tap exactly at the midway of the 100 turns, that is at the 50th turn.
I’m looking for a way to adjust the phase of one antenna to match the phase of a second antenna for max signal.
Variable indicators and capacitors.
Sorry, I don’t think I have this circuit design with me at the moment…
salve sign swagatam sono un tecnico elettronico italiano siccome dovrei realizzare un semplice ricevitore radio in FM con 2 transistor e nel web ne ho trovati ma con risultati deludenti vorrei che pubblicasse un o schema o diversi schemi elettrici allo scopo grazie giuseppe
Hi giuseppe,
A two transistor FM radio will only work for radio strong FM radio stations which are nearby, it will not not be able to catch distant FM stations.
The third circuit from top is a tested design, you can try it.
Actually I want to know some details remote control coordination pls
Good day sir. There was an FM transmitter designed by you using bc547 and um66 and other passive components as remote control transmitter, while already-made radio was the receiver to trigger cd4017 to trigger relay to off/on a load. I want to ask, can this FM receiver using bf494 and bc559 get the signal from the transmitter
of um66 and bc547 designed by you? Thanks
Hello Emmanuel, I guess you are referring to the following post:
https://www.homemade-circuits.com/how-to-make-fm-remote-control-using-fm/
You will get a much higher range if you use an actual FM radio for the above design, the range can be more than 30 meters. However using the single transistor version as the radio receiver, the range can be hardly 10 meters.
Sir, I don’t understand. Does it mean that the one transistor bf494, bc559 fm receiver can’t get the signal from bc547, um66- based FM transmitter(fm remote Tx) up to 30 meters?
Yes that’s correct! A proper FM radio has so many parts and sophisticated circuitry which makes it highly sensitive, that’s why its range will be more, whereas the single transistor FM radio is a crude form of FM radio so naturally its sensitivity and range will be much less than a full fledged radio.
Sir i don`t have BF494 transistor. So can i use others like 2N3904, BC547 2N2222 ……?
I think BC547 should work, you can try it.
Hi Swagatam,you mentioned that you are a manufacturer,what do you manufacture?
Hi Daniel, I used to manufacture automobile electronic products a few years ago but now I have discontinued it.
Sir….we r working on this project…….sir….why did u used 2 transistors….sir..? Is they r mandatory….but the concept itself is a fm radio with a single transistor…?…na sir…
Hello Sruthi, only the last diagram has two transistors rest all are single transistor. The extra transistor in the last diagram is for amplification so that a loudspeaker can be added in the design
God bless you sir .keep up the good work
Thank you for the quick response sir.pls since this circuit cannot transmit subwoofer signal ,can you please suggest me a better circuit to use instead?
You are welcome Muhammad, you can try the following transmitter circuit instead:
Make this Wireless Speaker Circuit
However, for the receiver you will have to use a small FM radio.
Hi sir, God bless you with this wonderful job u doing . Pls I want to know if I can use this circuit to make a wireless subwoofer?that is the receiver will be enlocsed in the sub woofer box.
And can bc547 be used instead of bf494?
Thank you Muhammad, I don’t think this circuit can be used for transmitting sub woofer signals, since the quality of the transmission may not be of H-Fi quality.
Hi !
Where can we get 400 ohm speaker my friend ? I’ve never seen such value of Speaker so far. Or ,instead, can we connect it any amplificator? Thanks in advance.
You can try a 100 ohm speaker, or simply connect an LM386 type amplifier with an 8 ohm speaker, or you can also try any of these transistorized small amplifier
Hi Swagatam,
Very interesting circuit. I have a question though. Instead of immediately soldering everything together, I’ve first tried to build the circuit on a breadboard. Understanding that this is not optimal, I expected that this would just give me a bunch of static. Instead, I get no sound whatsoever, except for a slight crackle when I connect/disconnect the battery. I double-checked all the components and used a multimeter to verify all connections are OK. Voltages across components are what I’d expect.
Can you think of a reason why the circuit would behave this way on a breadboard?
Hi Thom, any high frequency RF circuit should be strictly built by soldering and by assembling the parts close to each other. So a breadboard is big no for such designs.
Moreover, for stability the board must be attached with a large grounded plate, as shown in the first image.
If a professionally built PCB is used then the PCB must be ground plain type, meaning all the part connections must be surrounded with copper tracks
Hi Swagatam, that is very informative. As a relative beginner when it comes to electronics, I never realized that a breadboard would not suffice for testing high frequency electronics. Thank you for taking the time to explain this.
No problem Thom, please keep up the good work!
This transistors must work:
C945p: 450 mhz Ft
Bc237b: 250 mhz Ft
Bf199: 500 mhz Ft (works better than bf494)
2n3904: 300 mhz Ft
S9018: 1.1 ghz Ft (works better than bf494 and bf199)
S9014: 270 mhz Ft
Bc547b: 300 mhz Ft
Thanks
With coil
OK, then it’s fine
And can I use fixed capacitor instead of trimmer capacitor ?
Then how will you adjust and tune the transmission frequency?
Hi. Can I use bc556 and 2n3904?
you can use them.
Can I use bc 557 for amp
yes you can….
I built this circuit. but the output is very noisy. I hear only loud buzz sound
Did you use a base plate for the grounding as indicated in the first image?
I would like to make tuner amplifier
If possible will update it soon!
Hello Dear Sawgatam…
Please ..Can you Explain us how to replace the LC syntonisation input by the Varicap syntonisation system.. Thanks for All your posts.
Hello Youcef,
It can be a long explanation, so i would suggest you to refer to this article which has elaborately explained the theory:
https://en.wikipedia.org/wiki/Varicap
Can we get a Printed circuit board?
If you look at the schematic properly you will see that it is not missing but numbered differently .
Hi
R2 is missing in the last circuit. Is it ok
It was designed by elektor electronics engineers, if they have removed R2 in the last diagram it must be OK.
I think a single transistor radio would only make AM radio instead of the Multi channel FM radio and it only works if the signal really strong in your area. However if the signal is blocked or whatsoever this circuit may not work at all. I would prefer to use a IC that which make things easier.
Hi there sir 🙂
I want to know Is this circuit working perfectly?. because I have a project assignment to make a FM receiver without using IC. Your replied would be help me a lot.
Thank you sir.
Hi Hariz, this circuit was designed and tested by the Elektor electronic engineers, so this is a tested and a verified design, however this being a very small and a low tech FM receiver/transmitter circuit, the reception quality will be bad, and only the nearby strong stations will be received by this unit.
Sir I want to know if I can place an axial lead inductor of the same value in place of the coil L2
Ajekiigbe, you can try it, I don't think that would cause any issues….
A0A,SIR WHICH AMPLIFIER IS SUPPOSED TO USE ACROSS C6.
Any small amplifier like the following one, or if you have any readymade one will also do:
https://www.homemade-circuits.com/ic-lm-386-datasheet-explained-in-simple/
Sir, which capacitors and inductor make up the Colpitt's oscillator?
the basic idea is of a colpits oscillator, but different Colpit circuits might have slightly different method of operation….here the L, and the parallel C become responsible for the Colpits oscillator, according to me.
Ok. Thank you
Hello sir, in relation to the third circuit above, will the signal go A) up into the emitter and out the collector or B) will it go down and around and through the collector and out the emitter of T1?
Hello Wesley, The process could be much complex and it could be difficult for us to simulate the entire process in our mind.
Ok. Thank you sir.
Sir, what is the function of R1 and c1? And the function of the polarised capacitor and the 1k ohm resistor in the top right corner? And the function of c4 connected to the base of t2?
They all together along with the inductor for a regenerative kind of oscillator circuit
Ok. Thank you sir.
Hello sir, I have one question. What is the distance for the winding for L1 and L2? Like the total length of the winding?
Wesley, please do it as I have explained below
L1 which is the oscillator coil is an air cored inductor, meaning no core is required, wire is super enamelled type, 0.8mm in thickness, diameter of 8mm, with five turns.
L2 is wound over R6 itself using 0.2mm super enameled copper wire with 20 turns.
hello sir, i want to make FM transmitter and FM radio receiver 2 channel remote control car may you give me idea.
hello Karmchand, FM radio is not recommended, rather you can try the following concept
https://www.homemade-circuits.com/2013/07/simple-100-meter-rf-module-remote.html
Can someone tell me what R6? Sorry did not know
Thanks Rohit, you can try the following concept
https://www.homemade-circuits.com/2015/10/make-this-electric-scooterrickshaw.html
Dear sir,
I'm the big fan of yours
Kindly tell me about how can I make bldc esc at home.
Sir Please reply
My email rohitpandey2199@gmail.com
Dear sir
Kindly tell me about how can I make a home base radio station for what I need. For make a complete
My email kashifmehmood45@gmail.com
Dear Kashif, you can select any online 10km FM transmitter circuit and build it to make your home based radio station
Sorry,but I am talking about the 2 circuit for the l2 coil…and can you please post a photo of your succesful project from the top…..
L2 has no core for other circuits, it's air cored