High SWR does not

Discussion in 'Feedback and Suggestions' started by MJonesy, May 25, 2012.

  1. MJonesy

    Thread Starter New Member

    May 25, 2012
    This statement on SWR is incorrect "Also, a transmission line with a high SWR tends to act as an antenna, radiating electromagnetic energy away from the line"

    Transmission lines only radiate when an imbalance occurs in the line. Standing waves don't create an imbalance therefore no radiation is caused by the high SWR.

    Transmission lines used in Amateur radio (open ladder and coax) often have very high SWRs on them by design and no radiation occurs from them as long as they are well balanced.

  2. Wendy


    Mar 24, 2008
    Welcome to AAC!

    High SWR is caused specifically by a impedance mismatch, the power is being reflected back to the source because of it. The impedances are not balanced, it is the point. A typical consequence of high SWR mismatch is a fried transmitter as it is forced to reabsorb a signal it was never designed to handle. A portion of this signal would bounce back, exactly as it would with an antenna.

    This is the reason Balanced Lines (which is a form of coax, you called it open ladder) and Coax have a specific impedance rating.

    I've never heard the claim it would radiate, something like a coax would prevent that. I have heard of cases where the coax melted inside, causing egg shaped deformations in the coax where the internal insulation melted, ruining the coax.

    Given a antenna is basically a resonant standing wave I don't have too much problem with the statement it will radiate, though my verbage would be more along the line it could radiate. The center of an antenna is pure current (which is where the melting I was talking about occurs in coax) while the ends of the antenna are high voltage, with the signal bouncing between the two ends (resonant).

    We need the link however. We'll review the problem paragraph and change it where needed. About half the current crop of eBook Developers are HAMs, and are experts.
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    I've always had trouble believing this particular claim. I'll be interested to hear what the AAC radio operators say on the matter.

    This might be of interest.

  4. Wendy


    Mar 24, 2008
    In a sealed system I don't think it would radiate, but with high SWR you have some very antenna like things going on.
  5. Wendy


    Mar 24, 2008
    Well, preliminary ruling is the OP is correct. However, without a link as to where the problem is the feedback is not helpful. Anyone have the link?