Basic Radio

Appendix: Basic calculations

A large number of radio specifications involve the use of decibels. It is simply a ratio between two power levels using logarithms to the base ten. Although the basic unit is the bel, this is too large for most purposes and the decibel or dB, which is a tenth of a bel, is normally adopted.

Natural or Napierian logs can be used in the same way. In this case the units are nepers, but these are seldom used.

The number of decibels Ν can be calculated as below:

$N=10{log}_{10}\frac{P_2}{P_1}$

where P₁ and P₂ are the power levels being compared.

If these levels are expressed in terms of voltages V₁ and V₂ then the formula changes

$N=20{log}_{10}\frac{V_2}{V_1}$

Similarly ...