PECA's CSO/CTB & CPD Unit (Unit 3) is a subsection of PECA's Transmission Medium Impairment Simulator (TMIS) systems.

The TMIS CSO/CTB & CPD unit provides the means to generate, select and inject defined RF products specific to Forward (Downstream) transmission path Composite Second Order (CSO) & Composite Triple Beat (CTB) distortions and Return (Upstream) transmission Common Path Distortion (CPD) into test carrier paths.

The input to the CSO/CTB & CPD unit is a source of downstream multi-carrier (50 to 750 MHz), either a typical headend feed or a Multi-Carrier Generator (MCG).  The downstream multi-carrier source is split to feed three unique distortion generators; CSO, CTB, and CPD.

        The CSO generator consists of (6) single ended amplifiers in cascade and when driven into saturation by the multi-carrier source produces CSO products that are some 25 to 30 dB stronger than the CTB products.

        The CTB generator consists of (6) push-pull hybrid amplifier modules in cascade and when driven into saturation by the multi-carrier source, produces CTB products that are some 25 to 30 dB stronger than the CSO products.

        For proper functionality, narrowband filters (750 kHz @ 3 dB BW) are required to select the CSO and CTB components at the particular test channel/s.  These filters are user provided.

        The Common Path Distortion (CPD) generator consists of a diplex filter (High Pass 50 to 860 MHz and Low Pass 5 to 42 MHz) and a rectifier circuit.  The high pass input is fed by the downstream multi-carrier source.  The common port of the diplexer is connected to a biased Shotkey diode to produce the upstream spectrum.  The low pass section of the diplexer is connected to an amplifier to boost the desired level of CPD products

The CSO/CTB & CPD Unit can be controlled either manually, via front panel controls or via RS-485 interface for computer and automated control.

The computer (automated) control is via 1 I/O board, (two if filters are incorporated in the TMIS design) which are internal to the CSO/CTB & CPD unit and 1 or 2 PECA RS-485 SmartPlug Modules externally connected to the 25 pin D connectors on the I/O boards.

In a fully integrated test system, the PECA RS-485 SmartPlug Modules are daisy chained via RJ-11 modular cables between units. The chain is connected to an RS-232 to RS-485 converter on the RS-232 COM port of a PC or via PECA Unit 10.