Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Telecommunications terminology

  1. Feb 28, 2012 #1
    Hello, I have just started reading some telecommunications basic concepts. I have a question regarding the following phrase:

    "when considering that transmission lines are used in transmitting AC signals:
    R << ωL
    G << ωC
    In high frequency applications the R is so much smaller than the xL that R can be ignored.
    The G is so much smaller than xC that G can be ignored......"

    Can someone please tell me what the ωL and ωC terms mean ?
    What significance/meaning does the ω symbol have ?

    Thanks kindly for any help.
  2. jcsd
  3. Feb 29, 2012 #2
    reactance of inductor [itex]X_L= j\omega L\;[/itex] and reactance of capacitor is[itex] X_c=\frac 1 {j\omega C} \;\Rightarrow\; B_c= j\omega C\;\hbox { B is the subceptance.}[/itex]

    In Complex representation, impedance [itex]Z= R + jX[/itex] where X is the reactance. That where the two terms come in. If R <<ωL then Z=R+jωL≈jωL. Same as the other.
    Last edited: Feb 29, 2012
  4. Feb 29, 2012 #3
    Mr. Yungman explained it pretty well. But just to add:

    omega(ω) is your angular frequency. If you are in Europe, power lines are transmitting power at 50 Hz, in America, that is 60 Hz.
    But in telecommunications, this frequency goes higher. There was a method where you can send telecommunications signals through power lines! Those signals were at 800Hz or so, so they travelled down the power lines quite nicely. At the point where the receiver was, it was simply filtered out by a inductor.

    But as far as the physical explanation goes of ωL and 1/ωC, ωL is your reactance of L of your transmission line, as all wires have that.

    1/ωC is your reactance of C of your transmission lines. You see, when you send some HF signals through power lines, you get this parasitic capacity(as I imagine it) with ground, and that can be a problem, especially in power lines, where you need to compensate for that because it can give a major voltage drop.
    Last edited: Feb 29, 2012
  5. Feb 29, 2012 #4
    ωL and 1/ωC are reactance of L and C.
  6. Feb 29, 2012 #5
    Yes, sorry. Edited.
  7. Feb 29, 2012 #6

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    nowadays the electric companies run a fiber optic cable down the center of their power conductor and lease bandwidth to telcom operators.....
  8. Feb 29, 2012 #7
    I read back my original post, it's way too short to give good explanation. It's so short I can't even say it's "short and sweet"!!!!:rofl:
  9. Feb 29, 2012 #8
    I think I understood what you were aiming at. I am too green to know all terminologies correctly:D
    Last edited: Feb 29, 2012
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook