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What is the relationship between MHz and Mbps ratings of a fiber optic cable?

MHz is the frequency or rate at which a wave will cycle per second. 1 Megahertz would be equal to 10^6 Hertz or 1 million cycles per second.

Mbps refers to the how many bits of data is transmitted trough a media (such as fiber optic cable) per second.

MHz and Mbps are not equal, the confusion occurs because MHz works with analogue signals while a data transfer occurs digitally.

Transferring data rate (Mbps) to a cable is dependent upon encoding techniques. “Manchester” encoding is used for Standard Ethernet (10 Mbps), which is a two-level encoding technique that requires a minimum of 10 MHz. Cat3 copper cable offers 16 MHz and is why it was acceptable for Standard Ethernet.

To get higher data rates (100 Mbps) over twisted pair copper cable, a new four-bit encoding technique was required. Gigabit Ethernet (1000 Mbps) uses a PAM-5 encoding technique. Gigabit requires a minimum of 80 MHz, so IEEE specifies cable testing on all pairs up to 100 HMz.

Remember that 10 and 100 Mbps Ethernet uses only two copper pairs while 1000 Mbps uses four pairs. The following is a list of MHz and cable types (both twisted pair copper cable and fiber optic cable).

Twisted Pair Copper Cables

Category Bandwidth
Cat 3 16 MHz
Cat 5 100 MHz
Cat 5E 100 MHz
Cat 6 250 MHz
Cat 6a 500 MHz
Cat 7 600 MHz

Fiber Optic Cables

Fiber Type Core/Cladding Size (μm) Bandwidth 850/1300nm (MHz*km)
OM1 62.5/125 160/300
OM2 50/125 500/500
OM3 50/125 2000/500
OM4 50/125 3600/500
OS2 9/125 > 100 Terahertz*km

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