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Re: Antenna physical size & shape



Original poster: Ed Phillips <evp@xxxxxxxxxxx>

Normally a "tuned" antenna no matter what it's shape or configuration presents a resistive load of 50 ohms. If we load our Tesla coil with a 50 ohm resistor, the voltage will be trivial as it is for radio antenna's The top voltage is simply a function of power and resistance. At 10,000 watts into 50 ohms we get 707 volts..."

Have to disagree a bit. 50 ohms might represent the input resistance to an antenna feed with an impedance matching circuit. For example, the input impedance of a thin wire half wave dipole looks like about 73 ohms resistance in series with a reactance which depends on the exact geometry; a quarter wave vertical tower would be half that resistance. My 181 kHz transmitting antenna (50 foot tower) has a radiation resistance of only 0.03 ohms in series with a capacitance of about 450 uufd (~ 2000 ohms). The combined resistance of my ground system and loading coil is just a bit over 30 ohms so the net efficiency is only about 0.1% at the very best.

Ed