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Multiple Coax Cable Feedlines

April 14th Fact-of-the-Day

Most modern communications radios have 50-ohm unbalanced antenna connections, but many antennas have some different impedance that may or may not be unbalanced. A common solution is to use 50-ohm feedline with a matching and/or balancing device at the antenna-end. However, remote devices cannot be adjusted or replaced as easily as devices installed at a radio. A better solution in many cases is to use multiple coax cables connected in parallel or series as necessary to achieve an antenna match and then to install a matching device at the radio. For example, two paralleled 75-ohm cables create 37.5 ohm line. Three paralleled 75-ohm or two paralleled 50-ohm cables create 25-ohm line. Two seriesed 50-ohm cables create 100-ohm balanced line. Two seriesed 75-ohm cables create 150-ohm balanced line. Power is split between multiple cables, so inexpensive small cables can be used at higher power levels than if used singly. ©2005 Martek International All rights reserved.


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