Physics Topics can help us understand the behavior of the natural world around us.
What is Microwaves Frequency in Hz?
Carrier wave is used to remove the above two difficulties in distant communication of data signal. The wave is so named because the wave carries the data signal from transmitter end to receiver end. The main feature of carrier wave is that, its frequency is many times higher than the frequency of any data signal. In other words, its wavelength is much smaller than those of data signals. In this connection, it should be remembered that, the range of frequency of audio signal as data signal is from 20 Hz to 20 kHz and this range is called Audio Frequency range or AF range.
Each carrier wave is an electromagnetic wave. Normally, waves of lower frequencies from the electromagnetic spectrum are used as carrier waves. Generally these electromagnetic waves are radio waves and microwaves of frequency range of 3 kHz to 300 GHz. In the field of communication, the use of the residual part of the spectrum is almost non-existent.
Considering the different objectives and usages in distant communication, the carrier waves are classified into several categories as shown in Table 1.
Table-1
Category | Range of Frequency | Usages |
Very Low Frequency (VLF) | 3 – 30 kHz | To locate the position of ship or aircraft, to maintain the communication with submarines. |
Low Frequency (LF) | 30 – 300 kHz | To locate the position of ship or aircraft, AM radio. |
Medium Frequency (MF) or Medium Wave (MW) | 300 kHz – 3 MHz | Radio transmission of medium range. |
High Frequency (HF) or Short Wave (SW) | 3 – 30 MHz | Long distance radio transmission, different types of long distance communication. |
Very High Frequency (VHF) | 30 – 300 MHz | FM radio and TV transmission, weather radio. |
Ultra High Frequency (UHF) | 300 MHz – 3 GHz | TV transmission, mobile phone, Bluetooth communication. |
Microwave | 3 – 300 GHz | Communication through artificial satellite, radar. |
When a data signal is to be transmitted from one place to another, the suitable carrier wave is selected at the very beginning. From the table, it is clear that, the frequency which is suitable for radio transmission is not suitable for TV transmission.
Bandwidth: An ideal carrier wave is purely sinusoidal electromagnetic wave with a definite frequency. However, any attempt to generate a wave invariably results in the main frequency being superimposed with several other higher or lower frequencies. The intensity of the carrier wave is maximum for only its main frequency f0.
However, the intensities of other frequencies on either side of f0 diminishes gradually[Fig.]. Suppose that the intensity of each of the frequencies f1 and f2 on either side of f0 is half of the maximum intensity, which means that the rate of energy or power carried is also equal to half of the maximum value. These two frequencies f1 and f2 are called half-power frequency.
Only when the frequency gets lower than f1 or higher than f2, the intensity of the wave becomes negligible. So, through the main frequency of carrier wave is f0, the intensity or amount of energy carried by the waves between the frequencies f1 and f2 cannot be ignored. This difference of frequencies (f2 – f1) is called the bandwidth of the carrier wave. As data signal is superimposed on carrier waves, it is also called signal bandwidth.
Clearly, as frequency-intensity graph of Fig. becomes sharper, the bandwidth gets reduced. Hence the problem due to mixing of different carrier waves is also reduced. As per international norm for radio transmission, it is desirable that the band-width should not exceed 5 Hz, and the difference between two main frequencies (f0) of carrier waves, transmitted from two transmitting stations, should be at least 10 kHz. Each carrier wave of every transmitting station carries its own data signal. The carrier waves are recognised at the receiving stations, only due to the difference of their frequencies. Hence the data signals do not become fuzzy or unrecognisable by intermixing i.e., remain distinct from each other.