COFDM Radio Links
COFDM is the modulation format which allows a digital television to be broadcast in our homes in urban areas. The digital stream is transmitted on 2000 closely spaced carriers within a bandwidth of 6 – 8 MHz.
The transmission format is very robust and despite losing some of the carriers due to multipath and clutter the video picture is recovered. The COFDM’s ability to operate in a broadcast mode without a direct line of sight link makes it the most favoured modulation scheme for mobile video links involving person to control base, or vehicle to vehicle or aircraft to land video links. COFDM can also dramatically improve the covert surveillance of a battle front or terrorist route, where the equipment may be hidden or buried and retransmitted by a small repeater network back to a safe base.
IF Repeater
To enhance the system, and to allow the video to be viewed away from the scene of the threat, a covert IF repeater is offered which receives the signal from the COFDM transmitter, changes frequency, amplifies and retransmits to the control centre. The transmitted signal may be another channel in the same frequency band, or it can be in a different band eg. the unit receive a channel in the UHF band and retransmit a channel in S band. The IF repeater incorporates a linearised output power amplifier for 200mW, additional higher power amplifiers may be added covering 1 – 10Watts