data communications FREE cabling and networking Helpdesk
 Question by sazi ludidi posted 28 Oct 2004
 data communications
OK I have a couple of questions I don't understand:
1. What types of interference can affect the signal transmission on the cable?
2. What is meant by the term split pair?
3. Why is a split pair something to avoid?
4. The recommended maximum signal transmission distance using on a CAT 5 cable is 100 metres, why is this the case ?
5. How can the transmission distance be increased?
6. What are type of data encoding is used on CAT 5 cable if the IEEE802.3 LAN standard is followed ?
Can you tell? thank you.
 Answer by Joseph Golan posted 08 Nov 2004
Dear sazi,
1. Interference can come from a varity of sources. The most common one is EMI (Electroc-mechanical Interference) can be generated from motors, relays, transformers, high volage lines etc. The second most common type is RFI which is generated from radio signals. Both types of interference are induced into the cable. All cable can receive noise or interference but it is the signal to noise ratio which is important to determine. If the signal is high enoungh then the effect of the noise is minmal. There are many anti-noise methods used in the construction of cable. The 2 most comon or twisting of pairs and shielding.
2. A split pair is where a signal is split on two conductors that are not part of a twisted pair. An expample of this is analog voice communication (POTS) from your telephone service provider which is designed to work on a balanced twisted pair. The pair twists add to noise canceling of the pair's performance (see #1 above). If the sevice was delivered on two conductors from difernet twisted pairs, this would be what is commonly refered to as a "Split pair".
3. I think I answered this as part of number 2.
4. This is the standards set down with the EIA/TIA/IEE so all components of the system, despite being from different manufacturers can operate.
5. Distance can be increase by the use of active components designed for that operation.
6. For more information on IEEE802.3, visit and search for "IEEE802.3". You will find not only your answer (too long for here) but also other information on crosstalk.

Joseph Golan, RCDD

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