Intercarrier method: Difference between revisions

Revision as of 16:44, 28 October 2009

Revision as of 17:51, 28 October 2009

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{{main|Intermodulation}}

[[Image:RF Intermodulation at 280 MHz.jpg|thumb|200px288px|Image:RF Intermodulation at 280 MHz.jpg|thumb|A [[frequency spectrum]] plot showing intermodulation between two injected signals at 270 and 275 MHz (the large spikes). Visible intermodulation products are seen as small spurs at 280 MHz and 265 MHz.]]

When VF and the aural signal modulate the same carrier the inevitable nonlinearity of the electronic circuits cause unwanted signals which are called intermodulation products. (An example of intermodulation products can be seen in the accompayingaccompanying illustrationfigure at right, taken from the article [[Intermodulation]].) The unwanted signals appear on [[RF spectrum]] at regular intervals where the frequency differance of two unwanted signals being equal to the frequency difference of the two main signals.

In TV broadcasting the intermodulation products appear out of the [[RF band]] of the [[TV channel]]. So this intermodulation doesn't cause much trouble to viewers . However, out of band product means an unwanted transmission in the neighbour TV channels. For example intermodulation products of channel 7 appear in channel 5,6, 8 and 9. That is why notch filters are used in intercarrier system.