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3860 kHz Interference

March 9th Fact-of-the-Day

If you hear a rough-sounding and very broad signal centered at 3860 kHz there is a high probability that the source is a T1 data line within a half-mile or so. Internet data service provided by DSL, wireless, and various other means sometimes is referred to as T1 where the bandwidth approximates T1 bandwidth. However, they are not true T1 circuits and do not cause 3860 kHz interference. True T1 lines carry what is called a DS-1 signal. The data rate is 1544 kHz +/- 75 Hz. However, the transmission mode is bipolar using a code called Alternate Mark Inversion (AMI) which causes the pulse repetition rate to be 2.5 times the data rate. (2.5 x 1544 kHz = 3860 kHz) Signals at that frequency are sent in both directions down two 100-ohm twisted-pair balanced transmission lines that are often not shielded. Changing to shielded lines significantly reduces interference radiation. ©2005 Martek, International. All rights reserved.

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