Total posts : 45366
When thinking of a 50 kw AM station, how much of that 50 kw power flows along the outside of the transmission line from the tuner at the base of the antenna to the transmitter and is it part of the radiated signal?
Per the above responses it would seem a fairly substantial amount of RF would light up the cabinet of that transmitter.
From practical experience I would agree that radiation from a transmission line occurs when the load impedance does not match the transmission line impedance. But when properly terminated at both ends the only signal radiated from the transmission line would be due to imperfections of the transmission line itself which is usually minimal.
In the case of our coil loaded whip antennas, the coil reactance nulls out the capacitive reactance and leaves the radiation resistance of the whip which is on the order of tenths of an ohm plus ground losses. This does not present a 50 or 75 ohm load impedance and I would agree that the mismatch would cause common mode currents along the outside of the transmission line and result in radiated signal.
This is not the fault of the coax but rather that of a poorly designed antenna system.