MPX96 FM Stereo Transmitter

Modifications

The North Country Radio MPX96 FM stereo low-power broadcast transmittter kit was a bit of an ugly duckling when it was introduced in the mid 1990s. Consisting of a circuit board, a bag of parts and several xeroxed instruction sheets, the kit was not suited for the novice kit builder. Nor was it suited to someone without an oscilloscope and a firm knowledge of the principles of the circuit's operation. However, for someone with the requisite building skills, knowledge and test equipment, the MPX96 could be turned into a swan.

Alas! Even properly built and adjusted, the completed original transmitter was flawed in a number of ways. The flaws are listed here in approximate order of importance (most important first). Some or all of these problems may have been corrected by the designers in subsequent versions of the MPX96:

The audio inputs were insufficiently low-pass filtered. This allowed high frequency artifacts in the audio signal, produced by the D/A converter of a CD player, for example, or the bias signal from a tape player, to beat with the 19 kHz stereo pilot. This was heard in the receiver as low level sputtering