[Antennas] VSWR on Log Periodic.

[Cletus W Whitaker]

de WB2CPN  South Central Pennsylvania USA  2002.04.27

Everything I know I learned from some one, so this is no exception. Which
means I'm never afraid to ask, no matter how dumb:

If I take my trusty Bird ThruLine Wattmeter and measure the indicated power
going into the transmission line, and the power coming back, then measure
the loss of the transmission line, why does that not tell me the level of
power arriving at the antenna and the level of power reflected by the antenna.
The usual SWR formula for P1/P2 should tell me the SWR at the antenna.  Or does
it?  If not, why not?  My early observations indicate that the SWR at the far
end of a shorted transmission line is Zero.  (My General Theory of Antenna
Activity states that the Current at the ends of a long wire or dipole antenna
is immeasureablly close to Zero.)  The truth is mixed in here someplace.
As some one said, the actual SWR of the antenna (the load) is always greater 
than what's measured at the transmitter end of the transmission line, (safely
assuming that all transmission lines do have loss of some value or other).
73  Clete