Friday, January 4, 2008

Digital Signals over Radio Waves

Frequency - rate at which current (voltage) cycles occur, that is, number of 'waves' per second

Radio waves occur in electromagnetic spectrum between 1Khz and 1Terahertz.
Cable uses part of RF spectrum.
Cable can transmit simultaneously in both directions, RF portion is split in to :
i) Downstream - Head --> Subscriber at 810Mhz of RF Band (50 --> 860Mhz)
ii) Upstream - Subscriber --> Head with 37Mhz of RF Band (5 --> 42Mhz)

Downstream Frequency is split in to channels (6Mhz in US, 7-8Mhz in Europe)
TV Spectrum:
VHF low band = tv channels 2-6
VHF Mid band = tv channels 98,99,+14 to 22
VHF High Band= tv channels 7 to 13
VHF Superband = tv channels 23 to 36
VHF Hyperband = tv channels 37+

No channels for Upstream

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