RF basics

Try to find some basic books on radio frequency principles.
A steady RF signal, the carrier frequency, conveys no information other than the sender has money to spare.
The carrier can be modulated by altering the ampltude of the carrier. This is used on long wave, medium wave and short wave.
The carrier can be modulated by changing its frequency, This is used for VHF/FM.
Above this, digital modulation is used which is a mixture of modulation tecniques.
The frequency deviation is the amount of frequency wiggle.

Crystals are single crystals of quartz which vibrate at a frequency determined by their size. They can be used to generate a frequeny or to select a portion of a complex signal. 868MHz is too high for a crystal so if this frequency is needed, A frequency of one sixteenth of this may be generated and then multiplied by sixteen to get 868MHz

 

Standing waves will dissipate energy.
Standing waves will present a different impedance depending on the position of the wave. Altering a cable length may change or even stop the equipment working.