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Simplest AM Radio

The following circuit was taken from an old electronic book, it is indeed a very nice little two transistor radio receiver circuit which utilizes very few components yet is able to produce output over a loudspeaker and not just over headphones.

Simulation and Working


As can be seen in the given circuit diagram, the design is as simple as it can be, just a couple of general purpose transistors and a few other passive components for configuring what looks like a nice little AM radio receiver unit.

The circuit functioning is pretty basic. The antenna coil collects the MW signals present in the air.

The trimmer sets and tunes the frequency which needs to be passed across to the next stage.

The next stage which comprises T1 functions as a high frequency amplifier as well as a demodulator. T1 extracts the audio from the received signals and amplifies it to some extent so that it may be fed to the next stage.

The final stage employs the transistor T2 which operates as a simple audio amplifier, the demodulated signal is fed to the base of T2 for further amplification.

T2 effectively amplifies the signals so that it becomes audible over the connected speaker loud and clear.

T1's emitter has been configured as a feedback link to the input stage, this inclusion greatly enhances the performance of the radio making it extra efficient while identifying and amplifying the received signals.

Circuit Diagram


Simplest AM Radio Circuit

Parts List for a simple 2 transistor radio receiver with speaker


R1 = 1M
R2 = 22K
R3 = 4K7
R4 = 1K
P1 = 4K7
C1 = 104
C2 = 470pF
C3,C4 = 10uF/25V
T1 = BC547
T2 = 8050 or 2N2222
L1 = ordinary MW antenna coil
SPEAKER = small 2 inches, 8 ohm
TRIM = ordinary GANG

MW Antenna Coil on Ferrite Rod (L1)


MW antenna coil on ferrite rod

Use the Following type of GANG Condenser for the Trimmer (use the center pin and any one of the output pins from the MW side)



MW radio gang condenser variable capacitor

Need Help? Please leave a comment, I'll get back soon with a reply!




Comments

  1. can we seperate a smartphone mobile screen from its circuits making it wireless?its for a project.

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  2. Hi Tanmay,

    The overlapping broken lines suggest that these are NOT connected. The connected lines are shown with a black dot.

    P1 is a preset which has three leads, the center lead is indicated with a arrow head.

    As suggested by Mr. Shane, you can replace R3 with an small audio output transformer.

    The primary winding which has three wires should be connected in place of R3, while the secondary must be connected with a speaker.

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  3. 104 = 0.1uF

    T1 can be replaced with BC548, but T2 should be 1amp rated, any transistor rated at 1amp will do like 2N22222 etc.

    L1 should be a readymade MW antenna coil, any other type won't produce correct results

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  4. 1)Try BC557
    2)You can try winding it on any small ferrite former. Wind 1000 turns of 32 to 36 SWG wire, and over that 8 turns of 27 to 32 SWG wire.
    3)small RF chokes are definitely available in market.

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  5. IF trafo specs can be entirely different for different sages so it can be very difficult to set them correctly.

    You can find plenty of radio repairing guides online, just type the relevant keywords and Google it.

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  6. Thanks! Yes surely it can be done, you can the take the pickup to the amplifier from across C4 output and ground

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  7. Hi Tanmay,

    Here's the formula:

    XL = ωL = 2piFL
    where XL is the inductive reactance, ω is the angular frequency, F is the frequency in hertz, and L is the inductance in henries.

    Inductive reactance is the positive component of impedance. It is measured in ohms.

    You can use 4060 IC for making a simple timer

    Regarding the 810 circuit I can't say much without actually seeing it.

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  8. which circuit are you referring to?

    Anyway, yes definitely all trafos with prim/sec stages will have specific winding arrangements.

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  9. yes the winding will have definite start and finish points, the primary from up to down, while the secondary from down to up or vice versa.

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  10. recheck transistor polarity and antenna coil polarity, and connections.

    Under normal conditions no antenna is required for this circuit.

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  11. yes that can be done, you can incorporate a 7809 regulator for better response.

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  12. how do you add a variable tuning capacitor

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  13. the component indicated as TRIM is the variable tuning cap.

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  14. 1) There is an earthing symbol. How to earth in a circuit board?
    2) Can I use 8ohm/ 0.5watt speaker?

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  15. 1) earth symbol refers to supply negative line
    2)8ohm/0.5 watt will do.

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  16. i know R1 , R2 are resistances, but what signifies for R3=4K7? P1=4K7?

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  17. they have been calculated and placed for making the transistors conduct optimally as per the circuit specifications.

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  18. i mean , what i have to tell to the shopkeeper to buy? will he understand by "4K7"?

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  19. 4k7 means 4.7k, you tell him you need a 4 point 7 kay resistor.

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  20. Hi there sir Swagatam!! I have a few questions:
    1. What is the range of the radio(in KHz)?
    2. Area all resistors 1/4 watt?
    3. What kind of capacitor is c1 and c2? (I think they're ceramic?..just guessing..)
    4 Are c3/c4 an electrolytic capacitor?
    5. Is p1 a volume control?
    6. Is there a proper specs for trim capacitor, like something to tell the salesboy/girl in an electronics store?

    Thanks a lot!!! (apologies for those silly questions of mine...)

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  21. Hi Eshkariel,

    The range is the same as we normally have in all MW radios.

    all resistors are 1/4 watt
    C1/C2 can be ceramic.
    C3/C4 are electrolytric
    p1 is a kind of volume control
    trimmer capacitor can be a normal MW GANG condenser

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  22. umm...excuse me Sir do you have some good topic here to start for robotics?...just inquiring..Thanks...

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  23. sorry, I have not yet started anything related to robotics in this blog

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  24. HELLO SIR.what is the transistor 8050.There is any symbol before it like bc,2sc.can i build it in a veroboard. also can i use a gang from very old transistor radio made of metal

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  25. Hello Dibya, the prefix can be anything, it's not important, the number 8050 is the only unique assignment and you can tell this number to the retailer while buying it.

    yes a radio gang will do

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  26. Thank you sir. My house is about 100km away from radio station .Does this work for me.

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  27. Sir can i use 1895 IC audio amplifier to make the sound louder.
    Thank you very much sir . For your fast response

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  28. Sir please publish a MW signal booster.
    I had made many 6 transistor radio , 7 transistor radio and also 8 transistor , ic based 5band radio but two transistor radio is first time in my life.

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  29. sir plz tell me . Ac 128 transistor is available in Indian market.
    My grandmother's radio need to be repaired

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  30. Where can i add antina in this circuit

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  31. No, 100km is too far away, this radio will not work from this distance.

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  32. Dibya, you can use BEL188 if you don't find AC128, but AC128 should be available.

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  33. the antenna coil can be procured from any local electronic spare part retailer.

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  34. sure, if possible i'll try to post it...

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  35. in the diagram there's a symbol of variable capacitor but it said trimm...can you please clarify me about it, im working on this circuit...thanks

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  36. a variable capacitor is also referred to as a trimmer...but it's a PCB mount type not the Ganged type...although a GANG cap will also work equally well.

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  37. can you please post a picture of it, coz i think the man from the electronics shop gave me the wrong one....thanks a lot

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  38. Picture of trimmer :

    www.rshelectronics.co.uk/img/p/423-312-thickbox.jpg

    Picture of Gang:

    www.o-digital.com/uploads/2179/2184-1/Film_Dielectric_Variable_Capacitor_Pvc_Gang_426.jpg

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  39. thanks a lot...it really helps

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  40. ...what's the pin configuration of the 3 pin variable capacitor? (the square one).. thanks

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  41. use the center pin and any of the outer pin in the line...there will two sections for this, don't use the FM section, use the AM section....

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  42. ...i have another question C2 is connected to the ground and is it connected to R2? also R1 is connected to the coil and is it connected to the emitter of T1?.. thanks

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  43. the cross link connections are shown with a black dots....the cross links which are not connected are shown with white gaps....so the ones which are not connected with a black dots are unconnected with each other.

    R1 is Not connected to T1 emitter

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  44. ...hello what is P1? is it a resistor?

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  45. then C2 is connected to the ground only?
    another thing is that is the base of T2 connected to P1? and by the way is P1 a resistor?

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  46. C2 is connected to ground and R2 junction.
    T2 base is connected to R2 and T1 collector, P1 is connected to T1 emitter

    P1 is a variable resistor, a preset

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  47. ...i have another question, why did you use a NPN transistor and not PNP?, and why MW antenna coil?...thanks a lot....

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  48. NPN transistors are ideally recommended for all relevant circuit applications, PNP are just complementary and are used only when there's no other option left.

    MW antenna is used because the design is for receiving AM signals not FM signals

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  49. the variable resistor, is the center pin connected to the emitter of T1?

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  50. hi sir, can i replace the speaker with a 3.5mm audio jack instead and connect an amplified speaker externally? thanks :)

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  51. sir, i recently dismantled an am radio kit, i obtained the ferrite rode however there are 4 connections to the rod. there is 3 seperate coils of fire on it, of different turns...which terminals will i use sir, also after connecting the circuit, there is no sound produced. thanks much sir

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  52. Charlie, you can use the two end strands of the coil and the center tap which may be close to one of the ends of the coil....but make sure all the three wires have continuity with each other.

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  53. Good day sir, i reconnected the circuit and no sound produced still, however when i connected 9dc , there will be a 1second static then no sound anymore. i checked the capacitor and resistors and there is a voltage drop just to make sure that there is electron flow. I opened my am radio at home to make sure there is am signal reaching our home. is it that the speaker produced sound that is too small or there is something wrong with my circuit. hoping you can help me sir troubleshoot this mini project. thank you in advance sir. https://www.dropbox.com/sh/2w8f1dzn006lck6/AAA3oBds3I0QjRLXSCO3UddKa?dl=0
    as you said sir the three terminals of ferrite rod must have continuity...a b and c have precise continuity in kiloohms. whereas d has continuity also but much larger compare the 3 terminal.

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  54. also sir, how can we troubleshoot the circuit in case, for instance, if i remove the tank circuit and replace by short, should the speaker sound? how about removing inductor only? many thanks

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  55. Charlie, the antenna coil is the heart of the above explained radio circuit, if it's not of the specified type then the circuit will not respond, there could be other faults also which you will need to find by carefully checking the stages with a meter.

    by continuity I meant it should be 0 ohms....if it's in Kohms then that's not a continuity, that could be an open circuit and your meter might be showing something incorrect. because an antenna coil can never have kohm value.

    a breadboard assembly might not work, you might need to assemble it on a compact veroboard by soldering.

    you can initially use an earphone to test the unit instead of the speaker to get a better idea.

    and yes only very strong stations will be received by this circuit, moderately weak or weak stations cannot be received.

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  56. no, that may not be possible with this design...

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  57. Hi! What is the value of the trimmer capacitor in pF? and does MW antenna coil commercially available? Thanks!

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  58. Hi Matt, yes the antnna coil is the same which are used in MW radio receivers, and the trimmer capacitor can be replaced with any standard MW radio gang condenser

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  59. This circuit is quite useless.

    You have 4k7 into an 8 ohm load.

    One five hundredth !!!!

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  60. T1/T2 form a basic preamplifier stage, won't be a good idea to disturb anything in this stage, better to add another smaller amplifier stage after C4

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  61. By the way the circuit is not useless, it will work with a low output, you should think twice before commenting...

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  62. What is the value of the inductor?

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  63. very good site you, the article is good and neat, its contents useful once good joob at least you try together notes

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