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Scosche FMT4 transmitter update

Scosche transmitter & NOAA receiver. Added
antenna wire forms dipole with audio lead
A quick four years and three residences ago I set up a little NOAA Wx re-transmitter, broadcasting weather info to a few dozen neighbors for fun.
     The technology for that project included an old scanner, an old guitar compressor complete with foot pedal and a very slightly hacked low power FM  transmitter/car adapter from a big box store. 
     The Scosche FMT4 RA transmitter, for around $20.00, provided a bit of extra fun if a short wire (say, a quarter wavelength, for example) is attached to the negative battery terminal.
    Why would that have any effect?   As the circuit diagram shows, the manufacturer used a common, cost-cutting shortcut of connecting the antenna to the audio cable for a handy antenna and connected the RF ground to the ground bus on the PC board. 
     As this was intended to be a battery powered device, that should be the end of it.  The RF out is cleaned up with a capacitor / inductor first order filter before connecting to the audio cable and the RF ground ends at the bus.

Circuit diagram of the RF pins on the transmitter IC
     Unless, that is, someone puts a 1/4 to 5/8 wavelength wire (60" - 74" @ 100MHz) on the negative battery terminal, creating a radiator on the ground side of the transmitter and forming a crude, poorly matched dipole.
     Add a battery eliminator made from a recycled cell phone charger and you have an instant 24/7 operation.
     After four years of delivering NOAA Wx in a more convenient form, the original unit finally went buzz, crackle, hum and fell silent.
     Fortunately, I like the '4RA unit so much I bought two at the time so I had a back up transmitter I could put in service.
     There was some question as to how rugged these units might be when first discovered, now we have the answer - about four years of continuous use - two years longer than this model was on the market.  The FMT 4 RA was superseded by the FMT4 TFM in 2011.  The new model dumps the bank of micro switches for a progressive push button cycle when choosing frequency
     You can read much  more about this $20.00 ticket to low power radio fun in our "Freedom Stik" post.
Scosche FMT4 tuneIN Universal
FM Transmitter for iPod/MP3 Player
or broadcasting

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