Frequency Systems has developed a new constant impedance bandpass (CIB)
diplexer for combining the vision and sound signals at the output of
analogue television transmitters. Tunable to any channel in the UHF
band, the new CIB diplexer can also accommodate the different bandwidths
required for combining vision systems such as PAL, NTSC and SECAM, with
either AM or FM stereo modulated sound.
“The constant impedance bandpass circuit has advantages over constant
impedance notch diplexers, particularly for stereo sound operation,”
said RFS Broadcast Technical Manager, Graham Broad. “A CIB diplexer
can more easily deliver both minimal delay and the wider bandwidth needed
to accommodate the stereo sound signal.”
According to Broad, the diplexer is an extension of RFS’s leading
range of UHF combiner platforms. “The principles of operation
are the same,” he said. “The diplexer circuit is that of
a balanced combiner, where the narrowband and wideband inputs have been
replaced by sound and vision inputs.”
The diplexer utilizes the same components as RFS’s channel combiners,
with the exception of a new 2-pole filter body that has been specially
modified to accommodate the overall much narrower bandwidths (of the
order of 1 MHz) associated with vision and sound combining.
Currently available with a vision peak sync power (VPSP) rating of 5
kW, the diplexer range will ultimately be extended to include VPSP ratings
of 1 kW and 10 kW.