From: liz@poppyrecords.invalid.invalid   
      
   I'm still struggling to understand the way things work at VHF (145 Mc/s   
   to be precise).   
      
   As far as I can tell, the Velocity Factor of a piece of wire in free   
   space is 1.00  The VF of co-ax can be anywhere from 0.6 to 0.9 depending   
   on the dielectric but it does not depend on the type of wire as long as   
   the ratio of diameters is correct.   
      
   Therefore, if a piece of bare wire is dangling in the air I should   
   expect its VF to be very close to to 1.00, but if I dangled it inside a   
   bit of plastic plumbing, should I expect the VF to reduce, as it is now   
   surrounded by dielectric?   
      
   Would this be a large enough effect to notice inside a pipe of 22mm   
   diameter with a 2mm wall thickness made of PVC with some sort of filler?   
   (I have tried microwaving an offcut and it doesn't heat up.)  Presumably   
   any PVC insulation on the wire itself would also have an effect?   
      
   None of the websites on aerials seems to allow for this but they nearly   
   all suggest cut-and-try to get the final lengths right, which makes me   
   think that their calculations or measurements did not take account of   
   all the relevant factors to start with.   
      
   --   
   ~ Liz Tuddenham ~   
   (Remove the ".invalid"s and add ".co.uk" to reply)   
   www.poppyrecords.co.uk   
      
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