The last year has seen the launch of digital wireless camera systems by a number
of different manufacturers including Link Research Ltd. Digital Wireless Camera
Systems (DWCS) are intended to solve the problems associated with analogue
wireless camera systems.
Analogue wireless camera systems have been
available to the broadcast industry for decades, and are in common use at
sporting events for touchline coverage of football and pit lane coverage of car
racing etc. The analogue systems are essentially line of sight systems, meaning
that the FM modulation used requires an uninterrupted path between the
transmitter and receiver. In situations such as transmission in built up areas
where the transmitted signal can be reflected by a number of routes back to the
receiver (multipath interference) the analogue systems can suffer from picture
quality impairments such as ghosting, noise, chroma flutter or complete loss.
Viewers have become used to these impairments that can occur when watching in
car camera coverage or marathon coverage, typically when the transmitter passes
under a bridge or behind an obstacle. The traditional analogue systems therefore
have never offered true roaming freedom to the cameraman. Analogue wireless
cameras have needed labour intensive manual targeting of transmit and receive
antennas, to ensure a reasonable quality of link.
Suppliers of DWCS have
made great claims about freeing the cameraman, and offering a very rugged link
between the transmitter and receiver. This is possible, but it is only possible
in a correctly engineered system. It is the purpose of this document to
highlight some of the important technical factors that separate a truly rugged
system from a system that is only marginally better than analogue.
