Going back to the "antennas heating up".
I thought a bit about it.
I am not an antenna guru,but I think I have pretty much covered the situation in the following
If you think I'm talking crap,please consult one of the standard texts on antennas!
Antennas which are operating off resonance look reactive----- Capacitive for short antennas,& Inductive for long ones.
An antenna thus may be R -jX for the first instance,& R+jX for the second.
The value R in the above will be made up of R(losses) + R (radiation).
Where:-
R (losses) is normal resistance,& will remain the same over a large range of frequencies--it is normally for a vertical,earth resistance.
The resistance of the antenna itself for a metal antenna is so small as to be negliglble.(It may not be so in a paint antenna)
R (radiation) is the imaginary resistance which accounts for the"loss" which makes up the radiation.
Although it is not a "real" resistance,it meets all the other requirements of resistance.
When antennas are operated off resonance,the value of R(radiation) changes from the resonant value,so as well as X changing,so does R,BUT the loss part of R does not change!
An antenna which is not matched will reflect part of the RF drive to the Transmitter.
The reflected voltage & current waves are not in phase with each other,or with the incident wave at the load end of the feeder,but each combines with the incident waves at various points along the feeder,either adding or subtracting ,so that current or voltage maxima & minima appear along the feeder.
The voltage ones are better known to the general public--the famous VSWR!
Where current maxima appear,I^2 R losses occur due to the series resistance of the feeder,& when voltage maxima occur, losses
due to insulation leakage occur.--- The feeder gets warm,not the antenna.
If the Transmitter really is 50 ohms output impedance.the reflected signal is ultimately terminated,so there is no total loss of power,apart from the feeder losses already incurred.
But wait,there's more!----Modern solid state transmitters are equipped with a circuit which reduces the power output when confronted with a high SWR,so if the antenna is that badly off tune,the 100watt? will be reduced to a lower level.
Even if the antenna could become hot from being off resonance,there would be less power available to make it hot.
For quite a few years,I worked at a medium frequency AM Broadcast station which used a "Dual Mast".
This device was a top loaded vertical radiator,around 150m high,made of painted,galvanised steel,resting at the base on a very large insulator (about the size of a 200l drum).
The antenna was fed with a 55kW ,& a 10kW Transmitter,on different MW frequencies,via a combining unit.
Somebody noticed that the insulator had some kind of "scunge" on various parts of its surface & we were sent after closedown to scrub the insulator.
The thing had been running for around 19 hours straight,but by the time we got set up to do the job--say 3/4 of an hour,the metal of the mast was cold.
In fact,
everything was bloody cold!
If you want a reason to reassess your career path,lying on your back under tons of metal on a cold night,scrubbing an insulator with "Bon Ami" & distilled water will do it!