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Telephone FM transmiter, AKA phone bug

Posted on Thursday, January 5th, 2012 in DIY by DP

If you ever wondered how those phone bugs from spy movies work, here is the schematic for your very own. This simple FM transmitter uses a phone line to both power the device and receive the audio signal.  Just hook it up to the phone line you want to monitor and tune your FM radio receiver to the transmitting frequency. If you still have a land line, that is.

Via Circuit-Zone.

This entry was posted on Thursday, January 5th, 2012 at 11:00 pm and is filed under DIY. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

5 Responses to “Telephone FM transmiter, AKA phone bug”

  1. Torwag says:

    What’s a phone line…
    does this work on my iPhone or on my VoIP-asterisk box?

    come on don’t be so old-school ;)

    • Steve says:

      Yes, it will work with Asterisk; just hook up an ATA device. :)

    • Sean says:

      Phone line = audio in 600 ohm impedance.

      So, if you do a little impedance matching, bugging that IP phone will have you doing new/old style PI work in a jiffy.

      Now, given the size of the circuit, it’ll be a sledge hammer match for an iPhone.

      Though I’ve seen some miniaturized FM transmitter stuff around, hmm….

      • rsdio says:

        Don’t forget the 90 V triangle wave that shows up when the phone rings! (on top of -48 V DC) p.s. it’s 300 Ω impedance on the copper loop and 600 Ω when the handset is lifted, ending the ringing.

  2. Arup says:

    Bring back nostalgia. :)

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