S-meter

S-meter of an amateur radio device

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

Technical specification

The generally used technical definition corresponds to the recommendation of the International Amateur Radio Union (IARU) Region 1.

On shortwave , S9 is defined as the signal strength at which the receiver reaches -73 dBm , i.e. around 50 microvolt at 50 ohms impedance , on VHF it is correspondingly -93 dBm or 5 microvolt.

One step on the S-meter then corresponds to a level difference of 6 dB. Values ​​above S9 are given additively. On shortwave, for example, S4 corresponds to −103 dBm, −53 dBm is reproduced as S9 + 20 dB.

Scale in practice

In practice, this definition is rarely implemented. The reference value is almost always set differently in the device and the step size is often calibrated differently. Very few devices have a calibration button.

Conversion into other units

The signal strength can also be displayed in dBμV, dBm, watt or volt.

The formulas are:

• dBμV = 20 ⋅ log ₁₀ ( U _eff / 0.000001V)
• dBm = 10 ⋅ log ₁₀ ( P / 0.001W)
• P (in watts) = 0.001W ⋅ 10 ^{dBm / 10}
• Voltage (in volts) at 50 ohms = sqrt (50 ohms ⋅ 0.001W ⋅ 10 ^{dBm / 10} )

Comparison of common units for S-meters up to 30 MHz

S level	µV (at 50Ω)	dBm	dBµV (at 50Ω)
S9 + 60dB	50,060	−13	94
S9 + 50dB	15,830	−23	84
S9 + 40dB	5,006	−33	74
S9 + 30dB	1,583	−43	64
S9 + 20dB	500.6	−53	54
S9 + 10dB	158.3	−63	44
S9	50.1	−73	34
S8	25.1	−79	28
S7	12.6	−85	22nd
S6	6.3	−91	16
S5	3.2	−97	10
S4	1.6	−103	4th
S3	0.8	−109	−2
S2	0.4	−115	−8
S1	0.2	−121	−14

Comparison of common units for S-meters from 144 MHz

S level	µV (at 50Ω)	dBm	dBµV (at 50Ω)
S9 + 60dB	5,006	−33	74
S9 + 50dB	1,583	−43	64
S9 + 40dB	500.6	−53	54
S9 + 30dB	158.3	−63	44
S9 + 20dB	50.1	−73	34
S9 + 10dB	15.83	−83	24
S9	5.01	−93	14th
S8	2.51	−99	8th
S7	1.26	−105	2
S6	0.63	−111	−4
S5	0.32	−117	−10
S4	0.16	−123	−16
S3	0.08	−129	−22
S2	0.04	−135	−28
S1	0.02	−141	−34

Web links

Commons : S-Meter  - collection of images, videos and audio files

• S-meter scale generator. Retrieved August 15, 2015 . 

Individual evidence

1. ↑ International Amateur Radio Union Region I (1981). IARU Region 1 Technical Recommendation R.1. Brighton, England, UK.
2. ^ Hammonia Amateur Radio Club. The S-Meter ( Memento of the original from September 5, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. .