Radiowave and Microwave

Radiowaves span frequencies less than $1 {\rm GHz}$ . The higher frequency part of this band is used for radio and television transmission. There is no theoretical lower limit, and the familiar $50 {\rm Hz}$ power supply lines emits radio waves at this frequency which corresponds to a wavelength.

$$\lambda = \frac{c}{\nu } = \frac{ 3 \times 10^8 {\rm m}\, {\rm s}^{-1}}{50 {\rm s}^{-1}} = 6 \times 10^6 {\rm m}$$ (9.1)

The upper frequency part of this band, VHF(30 MHz$-$300 MHz) and UHF(300 MHz$-$3 GHz), is used for FM and television transmission whereas the medium waves(0.5 MHz $-$1.5 MHz) and short waves (3 MHz$-$30 MHz) are used for radio transmission.

Microwave refers to electromagnetic waves in the frequency range $1 {\rm GHz}$ to $300 {\rm GHz}$ or wavelengths $30 {\rm cm}$ to $1 {\rm mm}$. The communication band extends into the microwave.

The communication band extends into the microwave. Global system for mobile (GSM) operates in 900/1800/1900/MHz bands.

The earths atmosphere is largely transparent to electromagnetic waves from to $30 {\rm cm}$. Consequently, radiowaves and microwaves are both very useful for space communication and astronomy. This branch of astronomy is called radio astronomy.

In these two bands there are a large variety of electrical circuits and antennas that are used to produce waves for communication. We briefly discuss below a few of the astronomical sources of radio and microwave radiation.