Radio waves propagate or travel from one place to another in a sinusoidal wave form. One cycle of a radio wave is one complete set of values in a sine waveform. That means commencing from the start or mean position to maximum value, thereafter to minimum value and finally back to the mean or starting position. Speed of EM waves is equal to the speed of light which is constant in vacuum.
Amplitude of a Radio Wave
Amplitude of a wave is the maximum displacement from its mean position. Frequency in hertz is the number of cycles of the wave in one second. Wave length in meters is the distance travelled by the wave in one cycle. Frequency and wavelengths are inversely proportional to each other. Therefore, as frequency increases its wavelength decreases and vice versa.
Frequency and Time Period of EM Waveform
The frequency of the wave is same as the current which caused the wave. We are aware from our school lessons that the speed of an EM wave is the same as speed of light which is maximum in vacuum. Time period is the time taken by the wave to complete one cycle which is expressed in micro seconds which is 10–6 seconds
Variation in Speed of ElectroMagnetic wave
Speed of EM waves is equal to the speed of light which is constant in vacuum. Speed of a wave is the distance travelled by an EM wave in one second. You can easily say that the speed of EM wave is a product of its wave length and frequency. The speed varies with the density of the medium over which the wave is travelling. Over water, the speed is higher than the speed over land.
Relation between Frequency, Wave length and Speed of Radio Wave
Speed of EM Waves in Meters per Sec = Frequency in Hertz x Wavelength in Meters
Frequency in Hertz = Speed of Light in Meters per sec / Wave Length in Meters
Wave Length in Meters = Speed of Light in Meters per sec / Frequency in Hertz
Units of Measurement for Frequency
Frequency can be expressed as Hertz, Kilohertz, Megahertz and Gigahertz
- 1 Hertz = 1 Cycle Per Second
- 1 Kilo Hertz = 1000 Hz = 103 Hertz
- 1 Mega Hertz = 1000 K Hz= 106 Hertz
- 1 Gigahertz = 1000 M Hz= 109 Hertz
Frequency Bands
Radio waves are classified into various bands based on their frequencies.
| Band | Frequency | Wavelength | Radio Aids |
| VLF | 3 to 30 KHz | 100 to 10 KM | Submarine Communication |
| LF | 30 to 300 KHz | 10 to 1 KM | Non Directional Beacon |
| MF | 300 to 3000 KHz | 1000 to 100 M | Long Range NDB |
| HF | 3 to 30 MHz | 100 to 10 M | Long Range Communication |
| VHF | 30 to 300 MHz | 10 to 1 M | VHF Communication |
| UHF | 300 to 3000 MHz | 100 to 10 CM | Instrument Landing System |
| SHF | 3 to 30 GHz | 10 to 1 CM | RADAR |
| EHF | 30 to 300 GHz | 1 to 0.1 CM | Satellite Communication |
Phase and Phase Difference
Phase of an ElectroMagnetic wave is the position of the wave at a given instant on the sine wave form. It is expressed as 0 to 360 degrees of a circle. Phase Difference is the difference in phase between two waves. Phase difference can be obtained by phase comparison of the wave forms. However, you need to understand that phase can be compared only between waves of same frequency and wave length. Principle of phase comparison is used in some radio navigational equipment.