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   On Sun, 10 Mar 2013 06:43:13 -0700, dave    
   wrote:   
      
   >On 03/10/2013 06:30 AM, Don Pearce wrote:   
   >> On Sun, 10 Mar 2013 08:15:56 -0400, "Michael A. Terrell"   
   >>>   
   >>>    Heliax for 10 KW?  Ever had the filter fail on the compressor and get   
   >>> water in Heliax?  I had a stupid SOB for a boss 30 years ago who was too   
   >>> sheap to replace filtes on schedule and ruined a piece of 3" Heliax used   
   >>> at 4 GHz.  Waveguide is better at high power, and better than Heliax.  I   
   >>> had over 1700 feet of it at one TV transmitter.  It carried about 195 KW   
   >>> of RF to the top of the tower.  We had to maintain a set pressure of dry   
   >>> nitrogen on the waveguide to keep from compressing the sync pulses.   
   >>   
   >> No, not at 10kW. At 100W or so it is fine. On a long run I would   
   >> always opt for waveguide - tower dimensions permitting.   
   >>   
   >> d   
   >>   
   >You can't use waveguide for digital TV transmission-something about the   
   >joints making unsuitable anomalies. Air dielectric co-ax is what's used.   
      
   Hmm? Digital TV signals are regularly fed through my designs, which   
   are brimming with waveguide.   
      
   You may be talking about dispersion, though. Group velocity through a   
   waveguide is frequency-dependent, so with a long enough run, the phase   
   of the modulation gets distorted. You can pre-correct for this though.   
      
   d   
      
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