Am radio : oscilloscope......

Discussion in 'Wireless & RF Design' started by dmowziz, Apr 16, 2019.

  1. dmowziz

    Thread Starter Member

    Jan 18, 2019
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    Someone please assist

    When I probe (10ms/div) at point x without my LC then I can see 60hz noise (not so thick like image)...When I add the LC, the amplitude of the 60hz noise just increases...Please what is wrong?

    Also, where to connect the ground probe of scope?

    Thank you

    What kind of inductor? I am using a resistor like inductor.
     
    Last edited: Apr 16, 2019
  2. danadak

    Distinguished Member

    Mar 10, 2018
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    Could be coupling to the coil, the 60 Hz, AC power wiring in your lab.
    Turn off your AC in lab, and or flourescent lights. See if that helps.

    Scope probe goes to ground, the common in your schematic.

    Normally using a scope is a challenge because AM Radio signals often in the uV
    region. Depends on antenna, proximity to transmitter, propagation.


    Regards, Dana.
     
  3. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    'Scope ground goes to the point marked as earth on the diagram.
    What frequency is the LC tuned to?
     
  4. dmowziz

    Thread Starter Member

    Jan 18, 2019
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    Hi thanks...When I put the scope ground there then no signal on display...If I add an amplifier then use the battery ground, the signal is still 60hz but amplitude about 50v peak

    I've used different inductors (like resistors)...the last attempt, about 80khz...It's low?
     
  5. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    That's exactly what I would expect. The signal level will be too low to see on a 'scope.
     
  6. dmowziz

    Thread Starter Member

    Jan 18, 2019
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    hmmm, I dont understand...

    Suppose just antenna and LC with nothing else...Then probe to top part(x of image) then scope ground to bottom of LC : something should show on display?
     
  7. dmowziz

    Thread Starter Member

    Jan 18, 2019
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    Just seeing your post :( ....The scope ground : then no signal
     
  8. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    Only if you are very close to a transmitter and your probe didn't detune the LC.
     
  9. dmowziz

    Thread Starter Member

    Jan 18, 2019
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    "The signal level will be too low to see on a 'scope." why is this
     
  10. dmowziz

    Thread Starter Member

    Jan 18, 2019
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    fluorescent light reduces amplitude of signal : even after turning light off the signal does not increase again...

    why is this
     
  11. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    The received signal level will be low.
    I live approximately 17 miles from the UK National Physical Laboratory time signal. The signal covers the whole of the UK, and can also be received throughout most of northern and western Europe. So you might expect that I would see a strong received signal across the aerial tuned circuit but it is not visible on a scope. The level is uV not mV and that is why radio receivers need sensitive, low noise amplifiers for good performance.
     
  12. MrChips

    Moderator

    Oct 2, 2009
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    How long is your antenna wire?
     
  13. dmowziz

    Thread Starter Member

    Jan 18, 2019
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    Longer than my 'friend' MrChips..hehe
     
  14. MrChips

    Moderator

    Oct 2, 2009
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    I do not understand your response.
    You need an antenna that is more than 10 metres long and preferably outdoors away from any physical structures.
     
  15. dmowziz

    Thread Starter Member

    Jan 18, 2019
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    I used a sellotape to hold the wire on a wall (this isn't bad right?).... it works for an fm receiver i did (found schematic online)
     
  16. MrChips

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    You still do not state the length of the wire.
    Is it at least 10 metres long?
     
  17. dmowziz

    Thread Starter Member

    Jan 18, 2019
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    Yes it is
     
  18. MrChips

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    Oct 2, 2009
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    How long is the antenna?

    With a 10m antenna you ought to pick up a 50mV signal with a resonant LC circuit if there is a powerful AM radio station nearby.
     
  19. dmowziz

    Thread Starter Member

    Jan 18, 2019
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    I really dunno how long but not long enough : Will increase

    Please how to delete my account? or kindly do it for me please (Moderator MrChips)

    Thanks
     
  20. MrChips

    Moderator

    Oct 2, 2009
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    Why is it so difficult to state how long is your antenna wire?
     
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