coaxial cable

Discussion in 'General Electronics Chat' started by samwert, Jul 28, 2010.

  1. samwert

    Thread Starter New Member

    Jul 21, 2010
    7
    0
    why we cannot connect coaxial cable in place of electric wire or vice versa?
    what are the antennas used in mobilephones?
    someone please help me in answering these questions
     
  2. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    So that it do not pick up any stray signal or noise.
    And for mobile phones antennas depends, its different for GPS and CDMA and many more

    Good Luck
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Coaxial cable has special electrical properties that are desirable for RF signals. They really aren't designed to carry power, as the center conductor is virtually buried in insulation. In house wiring, the insulation is thin enough that heat can be dissipated through it.

    Sometimes, low voltage is deliberately placed on coaxial cables. For example, if the cable system in your home has an RF amplifier outside, a technician may have used a power transformer plugged into an outlet on the inside of the house, and used a special RF/power splitter to separate the RF from the power. However, it is a low power circuit, so the coaxial cable does not have to dissipate much heat.
     
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  4. samwert

    Thread Starter New Member

    Jul 21, 2010
    7
    0
    can you give some more insight over the explanation sgtwoookie
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    What do you want to know?

    RF transmission lines (ie: coaxial cables and other types) have a specific impedance. Your television coaxial cable has a nominal impedance of 75 Ohms. If the coaxial cable is bent or kinked, that changes its' impedance and it is permanently damaged. It will cause reflections in the RF signal, and may cause egress/ingress problems (signals leaking out and/or in). Commonly available 75 Ohm coax is RG-59 and RG-6. RG-59 should only be used for very short runs if RG-6 is not available. For longer runs, RG-11 might be used; it's still 75 Ohms, but much larger in diameter.

    Communications coax (like for citizens' band and "HAM" radios) is generally 50 Ohms impedance. RG-58 is used for short runs, RG-8 is used for long runs.
     
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