Radio Waves

Very Low Frequency – 3-30 KHz
Low Frequency – 30-300 KHz
Medium Frequency – 300-3000 KHz
High Frequency – 3-30 MHz
Very High Frequency – 30-300 MHz
Ultra High Frequency – 300-3000 MHz
Super High Frequency – 3-30 GHz
Extremely High Frequency – 30-300 GHz

Wave– is a progressive disturbance in a medium.

Frequency– is the number of waves passing a fixed point in a second. (Cycles per second).

Velocity– Distance traveled by a body in a unit time, in a particular direction, it has direction as well as magnitude.

Wavelength– is the distance covered by a wave in one cycle; it includes a crest and a trough.

Amplitude– is the maximum displacement of a moving body from its mean position.

Cycle– is a complete set of Variations.

Velocity of radio waves is as same as speed of light, which is 162,000 nautical miles/186,000 statute miles/300,000 kilometers per second.

Frequency = Speed of Radio Waves ÷ Wave length in Meters

Speed of Radio Waves =162,000n.m/186,000s.m./300,000 k.m per second.

Infra sonic Waves- Freq waves below 20 hertz.

Sound waves- Freq waves from 20 hertz to approx 20 KHz.

Ultra sonic Waves- Frequency waves above 20 KHz.

Critical Frequency- is that highest frequency at which a vertical incident ray to the Ionosphere will return to the Earth.

Critical Angle- Minimum Angle at which first sky wave returns to the Earth, and does not penetrate the Ionosphere layer.

Types of Modulation

Amplitude Modulation– In A.M. the amplitude of the carrier wave is made to vary in accordance with the audio frequency. The Frequency and the Phase of the carrier remains unchanged.

Factors affecting Amplitude Modulation-

  1. Construction of the Receiver equipment is simple, but the Transmitter is complicated.
  2. Single Side Band mode is possible.
  3. It has more bandwidth, and is subjected to more noise and interference.
  4. Requires high power Transmitter

Frequency Modulation– In Frequency Modulation, the Frequency of the carrier wave is made to vary in accordance with the Audio wave. The Amplitude of the carrier remains unchanged.

Factors affecting Frequency Modulation- 

  1. Construction of the Receiver equipment is complicated, but the Transmitter is simple.
  2. Single Side Band mode is not possible.
  3. It has wider bandwidth, because the frequency is made to vary in accordance with the audio wave, and is not subjected to noise or interference.
  4. It does not require high power Transmitters

Pulse Modulation– is used in the Radar; in this the pulses are sent in short intervals.

RADAR = Radio Detection and Ranging

Factors affecting Pulse Modulation- 

  1. It uses shorter Wavelengths, which can reflect the beams more efficiently.
  2. It has narrow beams, which can be used at shorter Wavelengths, and is not subjected to noise or interference