Total posts : 45366
I do not disagree with Rich’s analysis, but I would like to add some thoughts. What I did was a thought experiment and a little math to determine what would be required to deliver 100 mW. to the 30 ohm resistive antenna component assuming an ideal (100% eff.) transmitter and also assuming that the only power delivered to the final amplifier would be the real power delivered to the load (to stay legal).
Granted there are practical limitations which will severely reduce the efficiency of the system, mainly the inefficiency of common amplifier classes which may kill this approach. The volt amps in the load in this example is .099 + j8.29 or .099 watts + 8.29 VAR which would indicate that the I^2*R losses will be high, yet the current magnitude is only 58 mA. In my fantasy ideal situation, the transmitter will act as a constant voltage source (implies 0 output impedance) and will be able to provide the voltage and current without regard to the phase which is set by the load. This happens frequently in AC power circuits where there is a poor power factor (e.g. small fans, flourescent lights).
A key here seems to be a low or near zero output impedance which can be accomplished with feedback circuits (operational amplifiers for example have closed loop output Z’s in the tenths of ohms). Another view is that the reflected power is not dissipated in the transmitter since it sees 0 ohms.
I do realize that I am approaching this with assumptions about ideal circuitry but by doing so maybe I can get closer to ideal in practice.
***edit PS…a thought about what Rich wrote:
>It doesn’t matter from a power transfer and radiation viewpoint how much r-f voltage exists at an antenna feedpoint if no, or very little current is able to flow there. Without current, the antenna will not radiate the EM energy needed for its purpose.
You are correct but 144 volts applied to the model antenna impedance produces the maximum current constrained by the 100 mW limit for the final amp. The power dissipated in the radiatiion resistance will still be very small but that is the situation we have now and eliminating the coil losses will increase this power.