Belar Model TVM-100 TV Aural Modulation Monitor

The Belar DTJA-1 was conceived in response to the need for measuring clock timing errors in data streams carrying ATSC HDTV signals. The unit characterizes clock jitter and wander, and facilitates accurate determination of the data clock frequency†.

When fully configured, the DTJA-1 quantifies the three clock parameters of two different data streams: the SMPTE-310M data stream, which carries the MPEG-2 signal, and the 8VSB broadcast data stream. The DTJA-1 makes pinpointing the source of any timing instabilities occurring in the transmission path between the plant MPEG video encoder and the transmitter output quick and easy. A bridging loop-through connection permits on-line monitoring of SMPTE-310M signals right up to the input to the HDTV exciter.

The DTJA-1 is just 1 rack unit high. The unit is configured in one of two ways. The simplest configuration characterizes timing errors only of the SMPTE-310M data stream. With the addition of a circuit board, software enhancements, and RAM memory, the DTJA-1 additionally measures timing errors of 8VSB signals at an IF center frequency of either 36 MHz or 44 MHz.

The DTJA-1 verifies compliance with the SMPTE-310M program transmission standard for timing stability. Values of peak and RMS jitter are displayed on the front panel in nanoseconds. Alarm thresholds for the three parameters may be set either from front-panel-accessible menus or remotely, as in other Belar Wizard units. Front panel LED’s and rear panel relay closures are provided for the alarms. Remote readout of all indications on a PC is possible, on-site or off, via RS-232 and 100 base-T Ethernet connections on the rear of the DTJA-1. As an aid to diagnosis, the spectrum of the detected jitter is computed onboard and available via the two data ports. Connecting a GPS or other traceable 10-MHz time-base to a rear-panel input of the DTJA-1 facilitates precision measurement of data clock frequency.

† High values of timing jitter can cause receivers to fail to decode HDTV signals, as well as degrade HDTV reception in fringe areas. Excessive clock frequency error and wander may also prevent receivers from decoding or tracking HDTV signals.

DTV Data and Symbol Clock Timing Analyzer