XPost: sci.electronics.design, sci.electronics.misc   
   From: spam@spam.com   
      
   On Sun, 10 Mar 2013 04:21:03 -0400, "Michael A. Terrell"   
    wrote:   
      
   >   
   >upsidedown@downunder.com wrote:   
   >>   
   >> On Sun, 10 Mar 2013 02:43:08 +0000 (UTC), Cydrome Leader   
   >>  wrote:   
   >>   
   >> >>  Not many folks making hard coax runs anymore.   
   >> >   
   >> >this stuff was pretty darn old.   
   >> >   
   >> >are there power levels where they stil use wavegides and the like?   
   >>   
   >> In countries still using analog TV, the UHF final amplifier is often   
   >> implemented with klystron in the 100 kW range. The waveguide is quite   
   >> large, due to the low frequency.   
   >>   
   >> DVB-T digital TV transmitters typically operate with only 1-10 kW,   
   >> consisting of multiple redundant solid state modules, so there is not   
   >> much need for waveguides any more.   
   >   
   >   
   >How do you get that to the antenna without waveguide?  Coax losses are   
   >much higher than waveguide, and is less likely to have problems since   
   >there is no dielectric to break down.   
      
   Andrew's Heliax is pretty low loss, and good for VHF and UHF runs.   
   Dielectric amounts to nothing more than a thin spiral spacer - the   
   rest is all air.   
      
   d   
      
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