Harmonically Related Carriers (HRC)
Harmonically related carriers (HRC) is a system for assigning television channel numbers to bands of frequencies over a cable TV network. All vision carrier frequencies are on exact multiples of the channel bandwidth frequency (6 MHz in the case of System-M used in most countries of the Americas, other TV systems worldwide use 7 MHz or 8 MHz). William Grant, in his book, Cable Television, 2nd edition, GWG Associates, Schoharie, NY, 1988, page 82, states:
- "By harmonically relating the carrier frequencies themselves it is ... possible to improve system performance. This does not reduce the beats produced, but positions them within the system transmission spectrum, such that they are more tolerable. In effect, all signal carriers are spaced precisely at 6 MHz apart, and thus, all beats generated are at 6 MHz increments.
- Since the television signals are vestigial sideband modulation, if the beat products can be manipulated to fall on or near the RF carriers themselves, they are much less offensive."
Read more about this topic: North American Cable Television Frequencies
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