Radio expieriment gone awry???

Discussion in 'Wireless & RF Design' started by mbohuntr, Feb 8, 2014.

  1. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Here is the circuit I built to try and listen to SW at 3.5-4 MHZ. I used a 100 uH coil and 19pf resistor to pull in a station... I got AM1340????? I used a long piece of wire (15') out the window, and since I don't have my adjustable air cap yet, I just stuck a few small caps in parallel... Any thoughts?

    http://www.circuitdiagram.org/crystal-radio-with-amplifier.html
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    What radio station signals are you trying to pickup around 3.5-4MHz?

    If AM1340 is the closest AM radio station to you it is going to overwhelm any low power RF signals regardless of your simple LC tuned circuit.

    You are not going to have much success listening to SW on a crystal radio.
     
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  3. ian field

    Distinguished Member

    Oct 27, 2012
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    Some people enjoy the challenge of pulling in a signal at SW frequencies.

    If a resonant length antenna doesn't have much total surface area - improvise, run 4 or more parallel wires spaced apart a few inches.

    There's always the possibility of breaking with tradition and adding some gain - there used to be the Ferranti (IIRC) ZN414, that became obsolete and replaced by the MK484 - but I think that's also discontinued.

    Another difficulty these days is getting hold of suitable detector diodes, silicon types leave much to be desired. Germanium diodes used to be easy to salvage from AM/FM pocket radios, but they're not as abundant as they were, allegedly Shottky-barrier diodes work just as well as germanium, perhaps BAT84 or 1N6263 might work - power ones like 1N5817 are likely to have too much junction capacitance.
     
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  4. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Mostly just trying to pull in any local DXers in that band. Something new to play with besides sensors and alarm circuits... I guess I thought it might be fairly easy..... :rolleyes:
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    MK484 is listed here.
     
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  6. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Thanks! I will have to explore this some more..
     
  7. vk6zgo

    Active Member

    Jul 21, 2012
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    A basic crystal set is just that---basic!!

    Some very knowledgeable people do specialise in listening to SW on crystal sets,but these are quite complex designs,& they mostly listen to high power International Broadcasters.

    Apart from these,there are very few Amplitude Modulated stations present on the HF bands.
    If you want to hear "Hams" around 3-5----4MHz,you need something which will resolve Single Sideband & Morse (called CW for complex historical reasons),signals-------crystal sets will not.

    In simple Receivers,your choice is now between Regenerative & Direct Conversion Receivers.
    Both can give quite good results,with the latter usually superior,but perhaps not quite so "Noob -friendly".:D

    I suggest you Google for both.
     
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  8. bertus

    Administrator

    Apr 5, 2008
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  9. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The shown receiver is one of the regenerative kind.
    Keep in mind that the receiver may "oscillate".
    The trick with this kind of receivers is to have the input transistor just below the oscillating level.

    Bertus
     
  11. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Is that the reason for R3? Could the output be ran through the 386 amplifier for some volume control instead of earphones?
     
  12. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The headphone is connected from the +9 Volts to R8.
    If you want to use a LM386 as amplifier, you can leave the R7,R8 and Q3.
    Connect the input of the LM386 to C9.

    An other project that might interest you is shown in the following link:
    http://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm

    It already has a LM386 for audio output and is designed for 3.5 - 6 Mhz and 5.5 - 11 Mhz.

    Bertus
     
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  13. ian field

    Distinguished Member

    Oct 27, 2012
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    There was a crystal set idea that I believe originated in America, the push-pull detector. Start with a twin gang tuning cap with equal sections and wind 2 tuning coils, each has its own detector which it drives in opposite phase to the other. The 2 cathodes join at the filter cap and the 2 signals are summed.

    More sensitive - but IWHT any difference between the 2 sections would work against selectivity.
     
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