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22 Oct 2010

lucidscience.com has build a 2 transistor Spy Transmitter that will send the sounds picked up in a room to any FM radio tuned to the same frequency as the transmitter. Check construction details on the link below. [via]

This project is focused towards those who have not yet attempted to build any kind of RF project, and it is laid out in such a way as to make it easy to explore the basic principles of RF circuitry and ensure a successful final product.

Tiny 2 transistor Spy FM TransmitterĀ – [Link]

One Response to “Tiny 2 transistor Spy FM Transmitter”

  1. Audioguru Says:

    The circuit is poorly designed and [b]will not work[/b];
    1) The first transistor is biased wrong so it is saturated all the time. If you scream loudly at the microphone then the first transistor will suddenly blast very loud extreme distortion.

    2) The antenna is connected directly to the LC tuned circuit so the frequency changes if anything moves toward or moves away from the antenna because then the capacitance changes.

    3) The 0.22uf capacitor C3 reduces audio frequencies above 1.2kHz instead of boosting high frequencies like FM radio stations do (pre-emphasis). Then the sound heard on a normal fM radio that has de-emphasis will sound extremely muffled. C3 should be 470pF (its value should be 468 times less).

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