The R.L. Drake model MQM6000L is a professional quality, digital headend modulator that accepts one to six single or multiprogram transport streams via six BNC, Asynchronous Serial Input (ASI) connectors. When six streams are input, the MQM6000L then multiplexes one program from each input and applies the result to the QAM modulator and up converter for output onto any desired CATV or off-air output channel between 54 and 1002 MHz. A program filter is provided to allow selection of the desired program from each input stream. Other programs in the incoming streams are dropped.