What affects the size of the amplitude of a wave sent by an antenna?
The amplitude of the signal fed to it.
And the efficiency of the antenna.
The impedence matching between the source and the antenna(kind of inclusive with the above two). The length of the antenna vs the frequency of the signal sent to it.
You're saying that the frequency has to do with the amplitude? Whats the formula anywayz?
Yes I am. Antennas have to be 1/2 of the signal wavelenght for optimum transmission (1/4 waves use ground for the other 1/4 of the antenna length) http://www.electronics-tutorials.com/antennas/antenna-basics.htm
So, if your antenna is not the correct length then part of the energy put into the antenna will be lost. http://www.ycars.org/EFRA/Module C/AntVert.htm
It is useful to think of the equivalent circuit of the antenna as a series circuit it comprises 4 parts L C R1 R2 , R1 is the radiation resistance , R2 is the loss resistance L and C are the inductive and capacitive elements .
Ideally L and C tune out if the signal frequency matches the antenna type and configuration . The part of the signal important is that across R1 typically a few 10's of Ohms , usually r2 is not too high and in many cases can be ignored , but the tuning
is important since typical antennas like a dipole are quite high Q meaning that the L impedance is higher than R1 and this must by cancelled by the C impedance .
In cases where it matters the antenna impedance will be measured and any tuning
done ( sometimes by an externally added C component or matching circuit ) .
Antennas do NOT have to be tuned alone -- small antennas as used in portable equipment (pagers ) cannot self tune -- so they are tuned by other components -- they can still be efficient . in Antenna design suitable software is often used which
indicate impedances losses and directional information .
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