RF signal amplitude
Last Post: July 25, 2006:
it is mentioned in the cwna study book that frequency (therefore wavelength) and phase are dependent on the change in amplitude with time whereas the polarity is not ...can anyone explain this relationship
RF signals are always A/C (alternating current), which means that their amplitude oscillates between two extremes. Frequency is a measure of how often the amplitude oscillates within a certain amount of time?¡é?€?¡±for example, 2.4 GHz = 2.4 billion oscillations per second. Wavelength is a measure of how far the signal travels in a single oscillation. With a little examination, it can be seen that frequency and wavelength are just two different ways of looking at the same quality of the signal. If the propagation speed of the signal is known, its wavelength can be calculated from its frequency, and vice versa.
Phase is a way of expressing the relationship between two different signals having the same wavelength/frequency. Phase expresses whether the two signals are peaking (maximum amplitude) at the same time, whether one signal is peaking while the other is troughing (minimum amplitude), or anything in between. Since phase is a way of measuring a relationship that depends on wavelength and frequency, it can also be seen as related to amplitude.
Polarity, on the other hand, is not related to any of the previously-mentioned qualities, and is separate from amplitude. If the RF signal can be imagined as a string, vibrating with a certain amplitude and frequency, then polarity is the plane in which that string is vibrating. If we imagine a clock face, one RF signal might be vibrating in the plane that runs between 12 o?¡é?€??clock and 6 o?¡é?€??clock, while another might be vibrating in the plane that runs between 9 o?¡é?€??clock and 3 o?¡é?€??clock.
Amplitude, wavelength, frequency, and phase are most affected by the transmitting radio, while polarity is most affected by the design and orientation of the transmitting antenna.