10base2 Ethernet

Discussion in 'General Electronics Chat' started by irastha, Mar 10, 2009.

  1. irastha

    Thread Starter New Member

    Mar 6, 2009
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    Hello all,
    I have been reading articles for 10base2 ethernet connection. Everywhere its written that we should not connect coax between the T connector and the device. The end of T connector must directly be connected to the Device.
    Can anybody please share the reason behind it.
    Thanks a lot
    :)
     
    Last edited: Mar 10, 2009
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Yep. A properly terminated transmission line looks like 75 ohms at all points along the line. If you bridge across the line with an infinite impedance device (which the input impedance of a proper Ethernet card approximates) it won't cause any reflections to occur in the line. However, if you have a length of transmission between an ethernet card and the "bus" transmission line, it can actually look like a dead short 1/4 length back, and at other distances, it can look like a big inductor or capacitor...not good. You might look up some references to the Smith Chart and transmission line theory.

    Eric
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Just a few quick notes:
    10base2 used an impedance of 50 Ohms.
    RG58 was typically used.
    Total length of the coax was limited to around 600 feet.
    A 50 Ohm terminator was required at each end of the "daisy chain".
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Yer right! It was 50 ohms. At least it was SUPPOSED to be. It seems a lot of people threw together systems with 75 ohm cable TV coax because it was so cheap. :) Never seemed to make too much difference. Now, forgetting the TERMINATION resistor DID make a difference!

    Eric
     
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Just saw an article that someone at Iowa State university demonstrated succesfully running 1GB ethernet over 1000 feet of rusty barbed wire. Not recommended for your average installation though. :D

    Eric
     
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