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another FM transmitter project

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by hannobisschoff@gmail.com, Apr 14, 2011.

  1. Willen

    Willen Well-Known Member

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    I think I tested Current across C1 and it has load of divier+Q1 (on simulation). So simulation showing: -3.5uA to 3.5uA peak to peak. Then shouldn't I have to say "0uA, +/- 3.5uA" instead of "VDC"? Should we have to understand same thing if we used "VDC" or "uA" here? (But simulations says uA.)
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Yes, the current in C1 is AC (goes positive and goes negative) because it is a coupling capacitor. This AC current adds and subtracts to the current of the divider that biases the transistor.
     
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  3. Willen

    Willen Well-Known Member

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    I made this Lightning detector VERY carefully on quality PCB but I am not able to detect any sounds from lightning. Audio output amplifier (around IC) is fine. I had used 100k Pot instead of 10k on BS170 (pre-amp). Would it be the reason? If it is the reason I will add a 10k resistor with 100k pot to make 'poor man's 10k Pot'. Check this please! See this attach (for additional- go to this original link of project: http://www.techlib.com/electronics/spherics.htm )
     

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  4. dave

    Dave New Member

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  5. davenn

    davenn Active Member

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    are you getting any sound from it at all ? say a steady hiss ?
    if no audio at all, you need to check the audio amplifier stage for a start...
    feed a low level tone from an audio generator into pin 3 of the LM386 ... sound out of the speaker Yes ? No ?
    if no then look for a wiring fault arouond the LM386 and out to the speaker

    with lightning all you will get is a static crash, and you can pick that up with any radio receiver

    cheers
    Dave
     
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  6. Willen

    Willen Well-Known Member

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    ********** (double post deleted!)
     
  7. Willen

    Willen Well-Known Member

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    I tested Amplifier stage of LM386 it is good! I played a song feeding low level audio at the positive (signal) side of potentiometer and speaker is playing loud audio, it's working VERY well!

    Cannot understand about 'static crash'. OK then problem may exist on previous stage (detector)?
     
  8. davenn

    davenn Active Member

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    OK thats great ... but you didnt comment as if there was any static hiss coming out of speaker when trying to use the receiver

    static crash --- a very very old term for describing a short and strong burst of static. Anyone who has been into radio receiving for a short time would be familiar with the term
    Have you never heard lightning static bursts on a normal radio receiver ?

    Dave
     
    Last edited: Jun 15, 2013
  9. davenn

    davenn Active Member

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    OK that transistor is being usd as an audio amplifier, you could try a VERY small signal on the base of that transistor ... that is, between the detector diode and the transistor base to make sure the transistor is amplifying :)

    Dave
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Of course the very old lightning detector circuit does not work because you replaced its very high current gain MPSA18 bipolar transistor with a BS170 Mosfet that is completely different. It might work with an N-channel Jfet since it is simply a follower with no voltage gain.

    Where did you find a very old TL592 video amp IC that is only available in a surface-mount package today?

    There is no oscillator. It is simply a tuned RF amplifier with an AM detector.
     
  11. davenn

    davenn Active Member

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    AG thanks buddy .... I didnt pick up on that mistake that he made

    Its yet another case of people not following instructions.
    I had just finished chastising some one in another forum for taking a known working circuit, not building it to plan and then wondering why it doesnt work.

    Willen --- you found a working circuit, WHY change it ??

    Dave
     
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I doubt if the American parts are available in a "market" in India.
    The circuit might not work since its AM detector diode is biased positive so it probably does not work.
     
  13. Willen

    Willen Well-Known Member

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    Duplicate Deleted!
     
    Last edited: Jun 15, 2013
  14. Willen

    Willen Well-Known Member

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    Ops! Sorry! It's my writing mistake! I used MPSA18 (not BS170). I just changed a Pot. Because I didn't have 10k Pot for PCB suitable so I used 100k Pot. I have 3 pieces of TL592 in through hole package. The author of this circuit is Charlese Wenzel form Austin, Texas. He sent me all these needed semiconductors (as a gift :) ). I guessed some semiconductors from USA, but TL592P is marked as TAIWAN. Why USA imports Taiwan products? Wenzel made this device with these semiconductor (look a link I provided befor) so I think semiconductors are fine.

    I will test injecting very low sound in Base of MPSA18. If cannot detect lightning then will check tuner's and RF amp's wiring.

    Then should I have to test once with negative bias (<) (negative half cycles out?) ?
     
    Last edited: Jun 15, 2013
  15. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The AM detector diode is doing almost nothing because it has a continuous DC bias voltage from the output of the TL592 video amp.
    It will detect the AM from lightning much better if it is used as an envelope detector (AM rectifier) and is fed AC instead of DC. Then it needs a resistor to ground at its anode and is fed through a coupling capacitor.

    ALL American manufacturers have factories in China (Taiwan) because the labour and electricity are cheap. The Chinese workers take care of the factories but machines do most of the work. They burn coal in China to make electricity. It pollutes the air but it is cheap.
     
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  16. Willen

    Willen Well-Known Member

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    Here mod A or B? Or both?
     

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  17. Willen

    Willen Well-Known Member

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    OH GOD!!! HOW FOOL I AM!!!!
    I made this circuit almost 5 months ago and it was not working. I spent almost 10 days to design its layout on rough note, to design layout on computer, to make PCB, to drill and to solder. I had downloaded all needed datasheet too. I was VERY careful to make better circuit like professional! But today I found that I soldered MPSA18 in worng way!!! Wufff!!!! How non-sence I am!!! What happens to MPAS18 if I fed 12V to its base, emitter is same as emitter and collector is Audio IN (my worng connection), on this circuit? Is it damaged? If it is, I will change another MPSA18.

    However I want to modify for better AM detection as you said before. Look at my previous post and suggest me please!
     
    Last edited: Jun 17, 2013
  18. davenn

    davenn Active Member

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    considering most small signal transistors only require ~ 0.7 V to turn them on
    there is a high probability that 12V on it may have killed it

    do you have a transistor tester ?

    Dave
     
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  19. audioguru

    audioguru Well-Known Member Most Helpful Member

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    12V on the base and a 10k resistor to ground on the emitter results in a forward-biased base-emitter junction with only 0.13mA of current which will not harm the transistor.

    I think the original circuit uses the forward-biased diode as a peak detector since it feeds the 1nF filter capacitor and a very high resistance.

    It should be obvious that your circuit "A" has the diode always reverse-biased so it will never do anything.
     
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  20. Willen

    Willen Well-Known Member

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    Hi,
    If I connected reverse diode (1N4001) at parallel on supply of Mod4 (9V input) to make Polarity Protection Diode, will it draw another extra more current? Or any tiny disadvantage?
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A polarity protection diode is usually in series with the battery. But the battery voltage must be high enough for the 5V regulator to work and the voltage drop of the diode reduces the output power.

    If the diode is parallel with the battery then the battery is shorted by the diode if the battery polarity is backwards which will quickly kill a little battery.
     

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