S-Meter

An S- meter ( signal strength meter in English ) is a measuring instrument for indicating the signal strength at the input of a radio receiver, especially an amateur radio. It is used to quantify the strength of a received signal and is derived from the RST system.

Technical specification

The technical definition commonly used is in accordance with the recommendation of the International Amateur Radio Union ( IARU ) Region 1

Shortwave S9 is defined as the signal strength at which the receiver -73 dBm at 50 ohm impedance thus reached about 50 microvolts, to FM in accordance with -93 dBm and 5 microvolts.

A step of the S-meter corresponds to a level difference of 6 dB. Values ​​over S9 are given additive. In short wave corresponds S4 for example -103 dBm, -53 dBm are reproduced as S9 20 dB.

Scale in practice

In practice, this definition is seldom implemented. Almost always, the reference value in the device is otherwise specified and calibrated often also the increment differently. Very few devices have a calibration button.

Conversion to other units

The representation of the signal strength can also take place in dBmV, dBm, Watts or Volt.

The formulas are:

• DBmV = 20 ⋅ log10 ( Vrms / 0.000001 V)
• DBm = 10 ⋅ log10 (P / 0.001 W)
• P ( in watts) = 0.001 W ⋅ 10dBm / 10
• Voltage ( in volts ) = 50 Ohm sqrt (50 Ohm ⋅ 0.001 ⋅ W 10dBm / 10)