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Short wave radio on breadboard

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Discussion in 'Radio and Wireless' started by parthne555, Aug 26, 2020.

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  1. Aug 26, 2020 #1
    parthne555

    parthne555

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    Aug 26, 2020
    Hello,
    I have build a SW radio on bread board. I am using LM741 operational amplifier. But after powering it up it does not work. Please see the attached image of the circuit. 20200826_091716 (1).jpg
     
  2. Aug 26, 2020 #2
    Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    This is by no means a short wave radio.
    This circuit has so many flaws:
    1. negative supply of the LM741 is blocked by a 47 pF capacitor. SO there is no power to the opamp.
    2. The LM741 requires a minimum supply voltage of +- 10 V, see the datasheet. Operating it from a single 9 V cell is out of spec at the least.
    3. The "-" input of the LM741 is left floating. Even with a correct power supply the opamp will either go into saturation of oscillate wildly.
    4. I see no demodulator circuit. Do you use the input of the LM741 for demodulation?


    Where did you get this "circuit" from? It is imho completely useless.
     
    bertus likes this.
  3. Aug 26, 2020 #3
    parthne555

    parthne555

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    Aug 26, 2020
    Its UA741 Harald Kapp please see data sheet before saying "useless" to my project
     
  4. Aug 26, 2020 #4
    Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    How am I to know? you stated LM741 yourself.
    Please give correct information in the first place.

    Apart from the supply voltage which is +- 5 V for the UA741 (still a tad above the 9 V you are trying to work with) my other comments are still valid.
     
  5. Aug 26, 2020 #5
    parthne555

    parthne555

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    Aug 26, 2020
    So I removed the 47 pf capacitor. You were right! It was blocking the negative supply. Sorry Mr. Herald Kapp for providing you incorrect information. I got confused as I have both of them.
    I got this circuit from this YouTube video



    Please watch it. This guy gets confused in pin 6 and pin 7 of 741 opamp please ignore that and watch the rest of the video.
     
  6. Aug 26, 2020 #6
    parthne555

    parthne555

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    Aug 26, 2020
    This radio is nothing but a tank circuit resonating a particular frequency gives input to a differentiator(High pass filter). A simple SW radio(based on the frequency band it works best with).
     
  7. Aug 26, 2020 #7
    bertus

    bertus Moderator

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    Nov 8, 2019
    Hello,

    The UA741 also shows +/- 5 volts or 10 volts as minimum power supply.

    Bertus
     

    Attached Files:

    parthne555 likes this.
  8. Aug 26, 2020 #8
    davenn

    davenn Moderator

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    Sep 5, 2009
    UA741 is just a variation on a LM741 op-amp from a different manufacturer

    It's still just an Op-amp
     
  9. Aug 27, 2020 #9
    Audioguru

    Audioguru

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    Sep 24, 2016
    The video is missing a schematic and parts list.
    The antique 741 opamp was designed 52 years ago. It should be buried. Use a modern amplifier.
    The opamp has positive feedback instead of negative feedback.
    The radio is missing a Power Amplifier to drive a speaker.
     
    davenn likes this.
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