Multimode fiber for CATV

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 Question by Pete Walters posted 25 Aug 2000
 Multimode fiber for CATV
I do fiber and catv work. I have been asked to use an existing multimode fiber to transmit from a 27 channel HeadEnd to a proposed node/reciever.

There is -6.0dB loss at 1300nm and -8.4dB loss at 850nm. There is approx. 4920' (1.5km) of existing multimode fiber already placed the customer wants to use. I am familiar with singlemode fiber for high bandwidth transmission.

QUESTION: Can this multimode fiber be used? If so, does philips or other vendors make a transmitter and reciever set-up for multimode fiber? If this equipment exists, I am sure it is for 1300nm wavelength, but I really don't know. HELP! assume this is a 450Mhz H.E. loaded with 27 channels (300mHz).
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 Answer by Dmitri Abaimov posted 25 Aug 2000
Dear Pete,

Usually, CATV manufacturers don't consider multimode as an option just because it has pretty tight bandwidth limitation: 500MHz/km on 1300 nm cause by mode dispersion. Since most CATV networks are bigger than 1 km, it makes multimode transmission of high bandwidth TV signal useless.

In your particular case you have somewhat like 300MHz available for your 1.5 km link. Although most conventional multimode fibers have typical bandwidth limitation from 700 to 1000 MHz/km, your fiber doesn't look like very good one. You should expect something like 1.5dB loss for fiber itself plus up to 0.75 dB per pair of connectors. Since you have 6.0 dB loss, I assume the fiber is a pretty old one (or connectors are dirty or otherwise bad).

So far I never saw a head end equipment able to operate over multimode fibers, and I suggest that your customer is in the situation, when the only solution would be to place a new singlemode fiber cable.

Sincerely,
Dmitri Abaimov, RCDD

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