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@hotmail.com
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