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AM receiver

Discussion in 'Datasheets, Manuals and Component Identification' started by silver est, Apr 6, 2012.

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  1. silver est

    silver est

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    Apr 6, 2012
    The main problem why I think nothing will work for me in the first 2 years is that I consider many things unnecesary in circuits, so I just take them out :D. I have learnt programming through that hard work. Now I know how it goes. I need to start learning from the easiest things or it will not work for me. Anyone can give me the simplest example of a radio. Is there a possibility to catch all radio waves in a coil?
    Does the coil turns matter if I have a tuning capacitor?
    How to make the simplest portable radio so I could porbably see the radio waves with a really sensitive tester?
    Why is the ground even needed?
    If I connect a wire one end to other does it mean the wire now has a really little current because of radio waves?
    How do I catch those radio waves?
    A lot of questions :D and I really don't have anyone to answer me.
    Sorry for any misunderstanding and grammar problems.
    I am not English and I am kinda young.
     
  2. silver est

    silver est

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    Apr 6, 2012
    Why are some capacitors connected somewhere in the am receiver circuits?
    I've heard something about removing ultrasonic, but I have accually no idea why they are there. I dont even understand the capacitors clearly.
     
  3. davenn

    davenn Moderator

    13,620
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    Sep 5, 2009
    yes, cuz if you have too many or too few then the tuning capacitor and coil ( which is a tuned circuit) will not tune across the broadcast band

    The more simple you make it then it isnt not goingto be portable cuz of the need for a long antenna and a earth connection. The earth connection is needed for when you have very little gain in the radio and it along with the large antenna improve the reception

    not sure what you mean there ??

    the antenna catches the radio waves.
    modern portable radios dont usually need much of an external antenna and can rely almost totally on the internal coil on the ferrite rod ONLY because they have lots of gain in the many transistors and maybe an IC or 2 to make up for the lack of signal cuz of the lack of an external antenna

    that circuit link I gave you using the MK484 is probably the most simplest you could get and may be close to portable. well specially if you are not too far from the radio station transmitters.
    Else you will need a circuit that has probably at least 2 and maybe up to 3 or 4 transistors to get enough gain that you dont need an external antenna or earth connection

    So you can see that simplicity and portability do not go together. You are going to have to accept that you have either simple and need a long antenna and earth connection... or you can make something more complex that you are more likely to make portable :)

    cheers
    Dave
     
  4. davenn

    davenn Moderator

    13,620
    1,882
    Sep 5, 2009
    not really sure what you are referring to there
    ultrasonics ?? no

    have you a particular circuit and point out the caps in there and we ( myself or others) can tell you what the purpose of each one is ??

    Capacitors have many purposes for example ...
    in power supplies they can remaining AC signal on the DC power output.
    in audio circuits they can be used between stages to DC voltage isolate stages from each other
    in a radio circuit like what we have been discussing they can be used as part of a tuned circuit so the radio receiver will tune across a particular set of frequencies

    There's some basic ideas for you :)

    cheers
    Dave
     
  5. silver est

    silver est

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    Apr 6, 2012
    I hate the part of me that tells me that something is not needed. I accually left out the antenna and there is also no am broadcasts and I didn't tune it correct. I would really like if you would give me some kind of formula or calculator which could calculate the frequency.
    Also thanks for all the replies. They have helped me to understand this better.
     
  6. War_Spigot

    War_Spigot

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    Feb 20, 2012
  7. silver est

    silver est

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    Apr 6, 2012
    Thank you!
     
  8. silver est

    silver est

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    Apr 6, 2012
    But how do I get the inductance of a coil?
     
  9. silver est

    silver est

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    0
    Apr 6, 2012
    Does the antenna affect the inductance?
     
  10. davenn

    davenn Moderator

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    1,882
    Sep 5, 2009
    it can be measured with an inductance meter, or it could be worked out knowing the number of turns in the coil the thickness of the wire, and the diameter of the coil

    Am looking for a calculator for that :)

    OK here's one..... http://www.66pacific.com/calculators/coil_calc.aspx

    just as an example to get you into the ballpark .... 40 turns, 5cm diameter, 10 cm long will give 32 uH putting 32 uH into the other calculator along with 350 pF
    will give a resonant freq of ~ 1500kHz, right at the top end of the broadcast band


    yes it will have some effect

    for that LC circuit calculator war_spigot linked to, just as a started you should be looking at ~ 350pF for the tuning capacitor and looking for an inductor value that will give a frequency of ~ 1000 kHz ( roughly the middle of the broadcast band)

    Dave
     
    Last edited: Apr 10, 2012
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