[Antennas] Velocity factor for wire?

Tue, 20 May 2003 17:30:10 -0500

Work ethic alike
Carpenter, tailor, mohel
Measure twice, cut once!

Dave          W9LYA
What wrought doG hath?

On Tue, 20 May 2003 14:57:09 -0400 "Merv Stump" <[email protected]>
writes:
> Chris, I doubt that you will find a velocity factor for wire which 
> is
> general enough and accurate enough to be of much help.  However, 
> keep in
> mind the following:
> 
> 1.  The formula for calculating a half-wave length is 492/fMHz.  
> However
> the formula we use for calculating the length of a half-wave antenna 
> is
> 468/fMHz.  468/492 is .95.  Some of this differential is due to 
> "end
> effect" but most is due to the velocity factor.  So one might say 
> (with
> some reservations) that the velocity factor of wire is .95.
> 
> Now comes the "howevers"
> 
> 2.  The formula for calculating the length of a full-wave length is
> 984/fMHz, however as Orr and many others have documented full-wave 
> loops
> are electrically short so the formula we use for calculating the 
> length
> of a full-wave loop antenna is 1005/fMHz.
> 
> 3.  One more "however" - insulated wire is electrically long by from 
> 1
> to 3 percent.  Bottom line - when using insulated wire for an 
> antenna I
> use the appropriate formula and then reduce the length by 2%. 
> 
> All of which is why God made wire cutters and soldering irons, as 
> well
> as modeling programs. 
> 
> Merv, W2OE
> 
> 
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> 
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