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974RE: [loopantennas] Re: Transmitting loop

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  • W1EOF
    Aug 2, 2005
      The ghost you see on TV stations is multipath which is a result of the
      signals taking different length paths to arrive at your antenna. They run 6"
      coax made from thick-wall copper pipe. Inside is Teflon donuts supporting
      the inner conductor made from a piece of... thick it's 1" copper pipe.
      Running 50kw (carrier!) at 400mhz+ will vaporize the copper and Teflon
      within seconds. I've seen it.

      While it's true that most modern solid state finals have protection
      circuits, they are not fool-proof. I've never blown one up but plenty of
      guys have. That's what tells me theya re not foolproof. I suspect that the
      problem is when a fault occurs with a very fast pulse, one that is too fast
      for the time constant of the protection circuit. This would typically be
      more of a static or thunderstorm discharge kind of pulse, not an SWR related
      problem. That said I could envision a case where an SWR problem would cause
      an arc-over that would create a pulse fast and strong enough to destroy the
      finals.

      My $.02

      73,

      Mark W1EOF
      -----Original Message-----
      From: Henry Kolesnik [mailto:kolesnik@...]
      Sent: Tuesday, August 02, 2005 10:47 AM
      To: loopantennas@yahoogroups.com
      Subject: Re: [loopantennas] Re: Transmitting loop


      Dave
      I just wanted to point out that finals cannot dissipate power. All modern
      solid state finals have a protection circuit to decrease power output it the
      SWR rises so the resultant voltage can't damage the transistors. You can
      disconnect the antenna and power output will drop to zero fast so fast
      there's no damage. In TV stations that have long transmission lines a
      reflection ghost can be seen from the re-re-reflections if the SWR is not
      close to 1 to 1.

      ----- Original Message -----
      From: dldorrance
      To: loopantennas@yahoogroups.com
      Sent: Monday, August 01, 2005 7:21 PM
      Subject: [loopantennas] Re: Transmitting loop


      Hank, thanks for the distinction. However, even if the wave is
      re-reflected (back and forth around the speed of light about 1.6
      million journeys per second, to us mortals, for all practical purposes
      there remains a high voltage wave which is "standing" ie not moving,
      at the final transistor (or tube). Remember the wave tanks from high
      school physics? Those waves don't appear to move. They just stay
      put.

      Dave WA6YSO

      --- In loopantennas@yahoogroups.com, "Henry Kolesnik" <kolesnik@s...>
      wrote:
      > Reflected power does not heat up finals, it is re-reflected. High
      swr might exceed the voltage rating of the final transistors but
      reflections will not heat the finals.
      >
      > 73
      > Hank WD5JFR




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      If you've got links, post them in the Links section!
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      For uploading images, I prefer the Files section since Photos only allows
      everyone (except the uploader and moderators) to see a max of 300x400.
      http://groups.yahoo.com/group/loopantennas/files

      Put them in the appropriate folder, or create one.



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      a.. Visit your group "loopantennas" on the web.

      b.. To unsubscribe from this group, send an email to:
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