[TowerTalk] Quick Check for Coax Loss

[Pat Barthelow]

Folks,

If I wanted to check a long run of coax to a monobander (20 meter) beam, to 
see if there are any surprise unexpected losses,  I might disconnect the 
coax at the beam, and measure the indicated SWR at the radio.  Assuming the 
disconnected coax represented infinite SWR, one could just look from a 
chart, or from formulas to convert the indicated SWR at the Radio to coax 
loss... been there, done that....
Since it is a bit difficult to disconnect the coax at the beam on the tower, 
could I do a reasonably accurate measurement by exciting the 20 meter yagi 
with 10 meter RF, and assume the 20 meter driven element impedance at 10 
meters would be extremely high nee, >>10SWR, and measure the reflected watts 
at the radio, and compute the coax loss?   I guess what I really would like 
to know, is what (how high) would the feed impedance be on a 20 meter beam, 
if fed with 28 mhz RF, making it a nearly full wave, Hi Z load?

73, DX, de Pat Barthelow AA6EG aa6eg at hotmail.com