Source text. Published from the recorded source PDF for NEETS Module 10: Wave Propagation, Transmission Lines, and Antennas.
NEETS MODULE 10-Wave Propagation, Transmission Lines, and Antennas
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Q32. What are the two general types of variations in the ionosphere? Q33. What is the main difference between these two types of variations? Q34. What are the four main classes of regular variation which affect the extent of ionization in the ionosphere? Q35. What are the three more common types of irregular variations in the ionosphere? 2.12.3 Frequency Selection Considerations Up to this point, we have covered various factors that control the propagation of radio waves through the ionosphere, such as the structure of the ionosphere, the incidence angle of radio waves, operating frequencies, etc. There is a very good reason for studying radio wave propagation. You must have a thorough knowledge of radio wave propagation to exercise good judgment when you select transmitting and receiving antennas and operating frequencies. Selection of a suitable operating frequency (within the bounds of frequency allocations and availability) is of prime importance in maintaining reliable communications.
For successful communications between any two specified locations at any given time of the day, there is a maximum frequency, a lowest frequency, and an optimum frequency that can be used. 2.12.3.1 Maximum Usable Frequency As we discussed earlier, the higher the frequency of a radio wave, the lower the rate of refraction by an ionized layer. Therefore, for a given angle of incidence and time of day, there is a maximum frequency that can be used for communications between two given locations. This frequency is known as the MAXIMUM USABLE FREQUENCY (muf).