Re[4]: [TowerTalk] Steve's antenna study (GAIN)

[sbest@cushcraft.com]

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"The effect of  "reflected waves" or mismatches on the feedline and 
antenna system is only that apparent power handled by the feedline 
increases. If matched feedline loss is very low, the SWR can be very high 
and feedline and antenna efficiency nearly 100% even in a mismatched 
condition.
     
I operate lines with SWR exceeding 20 to one, and don't even give up a 
fraction of a dB doing so."
     
     I hope this does not come off as arrogant.
     
     The above statements are perhaps the biggest misconception in the 
     amateur hobby regarding antennas.  Antenna VSWR does reduce antenna 
     gain.  No question.  If you feed an antenna with a 20:1 VSWR you will 
     give up 7.41 dB of radiated power.  VSWR results in a mismatch loss 
     regardless of cable attenuation.   
     
     Antenna impedance matching, VSWR and mismatch loss have been one of 
     the principal aspects of my antenna design career.   When I worked 
     under contract with the US Navy designing and developing HF shipboard 
     antennas, impedance matching and reducing VSWR was the principal 
     concern due to power loss.  In some cases, we even used 3.5 inch 
     diameter air heliax coax (very low loss).  
     
     At of the companies I worked at, we actually constructed very detailed 
     1/48th scale models of Navy ships out of brass.  We would then 
     construct 1/48th scale model antennas and perform impedance and 
     pattern measurements at scale frequencies.  The results of these 
     efforts were translated into the design of full scale shipboard 
     antenna systems.  Once the antennas were installed aboard ship, we 
     would conduct full scale measurements and matching to ensure the 
     antenna worked as designed.  Again, minimizing VSWR was always the 
     most important issue. We were the only private company in the U.S. 
     that conducted 1/48th testing and design of this type.  
     
     I wrote a short article on VSWR, reflections and mismatch loss.  I 
     sent it to Ed (K4SB) to look at.  If anyone else would like to get it, 
     please let me know.  I would also be very happy to share some of my HF 
     antenna design experience regarding shipboard HF antennas.
     
     73 
     Steve Best

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