Intercarrier method: Difference between revisions

Revision as of 04:52, 23 July 2010

Revision as of 06:05, 28 July 2010

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{{main|Television transmitter}}

In TV transmitters, both AF and VF [[modulate]] [[intermediate frequency]] (IF) carriers. (The frequency difference between the two carriers is 4.5 MHz. in [[system M]] and 5.5 MHz. in [[system B|system B/G]]) Then the modulated IF signals are added either at the output of the [[Modulator|vision modulator]] or at the output of the vestigial sideband stage. In both cases, the added signals are low level signals and no special combining circuitry is required.

[[Frequency conversion]] and [[amplification]] is common. So a [[Electronic mixer|frequency convertor]] (or a mixer) and a series of amplifiers for aural signal as well as an output [[combiner]] are spared, which reduce the cost of the transmitter and electricity consumption of the amplifiers considerably. Although a [[Band-stop filter|notch filter]] to suppress the intermodulation products is used at the output of the intercarrier transmitter, the cost of the notch filter is not comparable to the cost of extra amplifiers and the output combiner. (See the subsection '''Intermodulation products''' below)