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FM Stereo for your Mono Transmitter

High quality FM stereo is available for your mono transmitter, at very low cost. This kit includes all parts, PCB and phono/RCA input and output sockets allowing easy hook up to your audio source and transmitter. No test equipment is required to set this unit up. The latest version is now on high quality double sided circuit board. This provides a large ground plane area that acts a screen which ensures reliable operation in RF noisy environments. In addition we have now fitted a 16 way IDE connection option, this can be used for the connection of power supply, left audio in, right audio in, multiplex out and 19KHz out. The 16 way IDE pins directly connect to the 16 pin IDE pins on our audio limiter boards, this makes connection of the stereo coder to two of our limiters, simple quick and easy using only a short length of 16 Way IDE cable and connectors.

Proven and Robust Design

This kit is now 15 years old and still going strong. The circuit is extremely reliable and will work in all conditions including high energy fields of RF. Basically you can install inside a transmitter with only little if none at all screening and it will still function correctly without instability or noise. We have not verified on a single test sample, this is proved over 20 years with the sale of over 4000 units.

How It Works !!

The stereo coder converts your existing mono Aareff transmitter into a high quality FM stereo broadcast transmitter. It will also work on transmitters from other manufacturers if the audio input is flat in amplitude and phase response up to 53 KHz. For the newcomers the coder takes a separate left and right audio signal on two separate cables and combines them together to form just one signal coming out on one cable. This unique signal is called multiplex and is fed into the mono transmitter. Any stereo tuner receiving this signal decodes the multiplex back into separate left and right audio signals. Stereo coder and receiver decoder synchronise to each other using a 19KHz pilot tone which is also added to the multiplex signal. Only the most expensive stereo coders will match the spec of this unit due to the pilot tone being crystal generated.

Technical Specification

Audio Inputs
Standard Line 0dBu 775mV adjustable

Audio Connection
Phono /RCA or via 16 pin DIL

Power Supply
11-16V DC

50 75 uS or none

Stereo Crosstalk
35 dB min

Audio Distortion
less than 0.01%

Pilot Tone
19 KHz +/-0.2Hz

Audio S/N Ratio
Better than 70dB

Audio Freq. Response
30Hz to 76KHz +/-0.5dB