System Design Considerations

Twisted Pair Requirements

Cable - The Twisted Sender will operate in a single pair or multi-pair cable of unshielded twisted pair (UTP) wire, stranded or solid. Individual pairs MUST BE unshielded, however an overall cable shield is acceptable with cables of 16 pairs or more. Other video signals, data and control signals or power supply voltages on other cable pairs will not cause interference if the individual pairs are twisted together.  If the Twisted Sender must be used with a multi-conductor (unpaired) cable, wires that are run adjacent in the cable should be used in order to achieve maximum common mode rejection.

Wire Gage - Wire between 20 and 26 gage is recommended in order to achieve optimum transmission distances. Refer to the Wire Reference Chart below. Twisted Senders will operate over a wide range of wire gages, with some possible sacrifice in transmission distance and or common mode rejection capability, depending upon the gage and specifications. Check with NIT for technical assistance at (847) 718-0600.

Wire Pairs - The copper pair must be isolated , having NO voltage, NO Loading Coils and NO capacitive lightning arrestors or devices connected to the pair. Any capacitive devices connected to the transmission pair will have the effect of swamping the high end video frequencies and limiting transmission distance.

Loop Resistance - Making an accurate determination of the length of the transmission pair is extremely important. Most installation problems with Twisted Sender systems are due to inaccuracies in determining the cable length. Total length can be measured with a simple ohmmeter by testing the loop resistance (total resistance of both wires measured at one end with the opposite end shorted). After measuring the Loop Resistance, refer to the Wire Reference Chart to determine the twisted pair length.

WIRE GAGE/LOOP RESISTANCE  REFERENCE CHART  

                     FEET
GAGE 1000 2000 3000 4000 5000 6000 7000 9000 11000
 20 20 ohms 40 ohms 60 ohms 80 ohms 100 ohms 120 ohms 140 ohms 180 ohms 220 ohms
 22 32 64 96 128 160 192 224 288 352
 24 51 102 153 204 255 306 357 459 561
 26 82 164 246 328 410 492 574 738 902



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