|Scosche transmitter & NOAA receiver. Added|
antenna wire forms dipole with audio lead
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|
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 The FMT 4 RA was superseded by the FMT4 TFM in 2011.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.
FM Transmitter for iPod/MP3 Player