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AM receiver circuit

Description.

Here is a low cost AM receiver circuit that can be tuned from around 550 to 1100 KHz. Three transistors are used in this project. The transistors Q1 and Q2 are wired as a compound transistor pair in which Q1 is an emitter follower and Q2 is a common emitter amplifier. The emitter follower prevents the loading of tank circuit, while the common emitter amplifier necessary voltage gain. The L1 and C2 forms the tank circuit.The L1 also does the job of antenna.The series combination of R6 and R7 gives a regenerative feedback between output of the Q2 and tank circuit. The transistor Q3 performs the demodulation of the carrier signal. It also provides amplification the demodulated signal. The audio output is coupled out from the collector of Q3 via the capacitor C3.Capacitor C6 provides some noise filtering.

Circuit diagram.

am-receiver


Notes.

  • The circuit can be assembled on a general purpose PCB.
  • Use a 9V PP3 battery for powering the circuit.
  • R7 can be used to adjust the sensitivity and selectivity of the circuit.
  • A high impedance head phone can be used for listening the radio.
  • For L1 make 60 turns of 26 SWG enameled copper wire on a 3/8 inch diameter, 3inch long ferrite rod.
  • The moving plates of C2 must be connected to the base of Q1 and fixed plates must be connected to the junction of C3 and R6.Reversing the connection may decrease the stability.

Some voltage values at different points on the working circuit.

Q1 (b) 1.31V
Q2 (b) 0.71V
Q2 (c) 1.34V
Q3 (b) 0.62V

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    40 Comments

    1. Makarand Sawant

      I don’t hv any simulator… So plz I need your help…

    2. Makarand Sawant

      Plz will anyone send me the PCB layout for this AM receiver circuit.. I suppose to submit this circuit tomorrow itself.. so plzzzz I need it now.. plz do help me…

    3. Fernando

      I placed this circuit in my computer simulator, it does not work. Q3 is not a demodulator, it is an amplifier. I went through the equations, there is no proof that this circuit is an AM demodulator. I would appreciate proof that this circuit is an AM demodulator to prove me wrong, and indicate where I may have made a mistake in my calculations. Thank you very much, and I look forward to hearing from you.

    6. Norman

      Nigusu, please go to http://www.theradioboard.com/rb/viewtopic.php?t=2498 for more information.

      Naseemsha said ‘sir. This circuit works well. But its volume is very low.’ There are some serious concerns about this circuit, look at the following quotes:

      R6 and R7 are ‘cut short to ground by the capacitor of 100N between the cold end of the tank circuit L1/VC1 and the ground. Because it has a very low impedance for the RF signal..’ (preceding is a quote from ‘DrM’)

      ‘And even if the “fedback RF” was not shorted to ground thru the cap, it still would not really be a regen. The Output would be fedback out of phase, because it is taken from the collector and fed back to the base(of the darlington) without any phase shifting components between. To get in-phase feedback would require either:

      taking the output from the emitter instead of the collector.

      OR

      placing a phase shifting component(a capacitor perhaps) between the collector output and the base input.

      Its actually a good thing that 100nf cap shorts any RF because otherwise it would be DE-generative!’ (preceding is a quote from Ham-er)

      Go to http://www.theradioboard.com/rb/viewtopic.php?t=2498 for all the discussion about this circuit.

    7. nigusu

      would you mind to send me the analysis for this ckt by my email.
      That is how the resistors are selected and which one is used as RF,MIXER,IF,AUDIO amplifier .thanks

    9. iyke

      again instead of 220nf 16v ….i used 0.22uf 50v will it work because i couldn’t find 220nf 16v

    10. iyke

      seetharam welldone but i could’nt find 10pf to extend my antena any alternative. And could you give me some terminologies concerning the circuit operation because i want to present it as my project or do you have any write-up. text me through my email

    11. ram

      Thanks seetharaman….but wat is pvc 2J ganged capacitor….? i didnt get u completly. I am from coimbatore,tamilnadu in india…how should i ask the seller,any specification…

    12. seetharaman

      Hi Ram buy a PVC 2J ganged capacitor and use both the sections in parallel

    13. ram

      hi all..i hav a doubt on c1…i dont hav a variable capacitor…how can i raplace it…i jus hav fixed capacitors….pls reply me..i am doing a project on this…my mail id is ramsaran.amrita@gmail.com

    14. seetharaman

      Hi Esam S1 is on / off switch for the circuit. The audio out, as this audio out cannot drive a speaker directly.you have to feed to any amplifier (like computer speakers) may be to your existing system.

    15. ESAM

      Hey guys,,, i wana ask what is the audio out,,, and is S1 BE the speaker ,,, thanks

    16. seetharaman

      Hi Jason use a plastic former (plastic conduit) of 10mm Dia wind using between 28 to 32 SWG any gauge closely wind 70 to 120 turns and use it as coil. If you have 10mm Ferrite rod wind 70turns of above wire use. This will pickup RF with higher energy. kindly refer to Vyakh’s reply.

    17. vysakh

      you can replce with resistor type. But quality may very poor according to the strength of signal. If your area near the transmitter, no problem. Otherwise will couse serious noise. aircore or powdered ironcore coils are normally used for this.

    18. jason

      can i ask something; the 200uH can be replace by a resistor type of inductor? pls answer thanks

    20. Naseemsha

      sir.
      This circuit works well.
      But its volume is very low.

    21. renekenshin

      Thanks SEETHARAMAN for the quick reply, but like the BC549, BC158 is also unavailable. I only have access to these transistor types – 2N3904, 2N2222, BC547/548 and PN100. If non of these works well i guess i had to give up on this circuit 🙁

    22. Seetharaman

      Hi Renekenshin you can use BC158B or C for better results. The audio output should be fed to an amplifier (like LM386, TDA2002 etc) before feeding to speaker.

    23. renekenshin

      Hi, can i substitute a BC547 or BC548 for the transistors? BC549 is hard to find in our place. And also, is the output strong enough to drive an 8ohms 1watt speaker?

    24. Seetharaman

      Hi Abdul you please buy PVC ganged capacitor PVC2J-25M or Mitsumi PVC22KT, parallel both the sections to get the required value.

    25. Abdul

      Hi,i’m 4rm nigeria i hoosed this cct as my final year project,my coplain is pls which other value can replace 500pf capacitor,because i ca ‘t find it near by.

    26. DIBYENDU

      I have a problem, how am I supposed to give the input in ‘MULTISIM SOFTWARE’if I simulate it in the software.

    27. Rami

      UNNI, well as for what type of capacitor to use you have two good choices: ceramic or electrolytic capacitors.. electrolytic usually dont live long or in other words the electrolyte in it gets dry and thus it affects their values significantly. but with ceramic you cant get high capacitance. i think you should use ceramic capacitors for all , but maybe you’ll have to use an electrolyte capacitor for C6. by the way, if u want to simulate it using a software you dont need to put C6, it’s put only because the wires arent perfect conductors.. as for the r7, you can just bring a potentiometer.
      i just have one question.. what’s the exact function of Q3??
      and how is the signal level at Q1 is 1.31 although a signal from an antenna isnt more than few microvolts? is it the resonant circuit that did this amplification?
      thanks for the schematic .

    28. byron

      THANK YOU FOR THIS CIRCUIT Chilero, IT WORKS IF YOU BRING SOME SMALL CHANGES BUT NOW IT’S ALL DONE, HAS RISEN TO YOU ONCE MORE THANK YOU, I AM FROM GUATEMALA.

    29. unni

      hai I am new in this site and novice in eletronnics
      how can i buy r7 from shop and also i want to no what type capasitor i use in this disc or any other?????

    30. Seetharaman

      Hi Junil L1 wound on the ferrite rod is the antenna. the ferrite rod will receive the magnetic flux available in the atmosphere. L1 & C2 are the tuned circuit will tune to the required frequency and resonate. if you want to connect any external antenna you can connect it through a 10PF capacitor to L1 which connected o Q1 base.

    31. junil

      hi all.. may i ask where is the antenna located in this circuit? where will the signal be received?

    32. Neeraj

      Thank you Seetharaman.. I’ll definitely try & tell you my result….

    33. seetharaman

      hi Neeraj use 2 to 3 turns loop (may be with 7 stranded insulated flexible wire) through which you feed your modulated signal and keep the loop close to L1. L1 will pick up your modulated signal Q1 and Q2 will amplify and Q3 will detect and feed the demodulated audio at the audio out.

    34. Neeraj

      Thank you Seetharaman.. But i meant how to apply the input signal [the already modulated signal] to the circut..

      I would like perform a stimulation of the circuit using a circut stimulator..

      I meant if i already have an AM modulated signal how should i give to the circuit? What changes should be made?

    35. seetharaman

      Hi Neeraj B1 is the 9volt battery through switch S1 gives the power to the circuit.

    36. Neeraj

      Thanks for the circuit!!
      I’m a newbie at electronic circits..
      Can anyone please tell me how & where to supply input to this AM receiver circuit ??

    37. somaye

      Hi,plz say me(mial me)the analyze of *AM resiver circuit in your site.

    40. V.Hari Hara Prasad

      Thank you for the circuits. I am a simple hobbyist who does not know about electronics, but can appreciate the gadgets. I live in India. Will you please give me some addresses of your people who live in and around ANDHRA PRADESH in India?

      Thank you for your service to the innovative ideas!

      All the best!

      prasad