From: jeroen@nospam.please   
      
   On 1/22/26 17:16, john larkin wrote:   
   > On Thu, 22 Jan 2026 09:29:10 +0000, liz@poppyrecords.invalid.invalid   
   > (Liz Tuddenham) wrote:   
   >   
   >> What physical properties determine the velocity factor of co-ax?  Most   
   >> of the amateur radio books give around 60% as the velocity factor for   
   >> 'common' types of 50-ohm co-ax.   
   >>   
   >   
   >   
   > V = c/(sqrt(Er))   
   >   
   > Solid polyethylene has Er around 2.3.   
   >   
   > Foamed stuff is lower.   
   >   
   > Polyethylene is awful. It melts when you solder it. Foamed is worse.   
   >   
      
   That's why we have crimped connectors.   
      
   > Your VNA measurement may be suspect.   
      
   Maybe. The VNA needs to be calibrated to move the reference plane to   
   the start of the cable, which is probably not at the same place as the   
   VNA output connector. At lowish frequencies, it probably doesn't matter,   
      
   Jeroen Belleman   
      
   --- SoupGate-Win32 v1.05   
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