Re: Antenna physical size & shape

["Tesla list" <tesla@xxxxxxxxxx>]

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