S-meter

Et S-meter (fra engelsk signal strength meter,^[1] dansk signalstyrke-meter) er en indikator som ofte er på kommunikationsmodtagere, såsom amatørradiomodtagere eller kortbølgemodtagere. Skalamarkeringerne er afledt fra det subjektive system til at reportere signalstyrker fra S1 til S9 som en del af RST-koden. Termen S-enhed kan anvendes til at referere til, hvor meget signalstyrkeændring, der skal til for at flytte en S-meter indikation fra en markering til den næste.^[2]

IARU Region 1 teknisk anbefaling R.1

International Amateur Radio Union (IARU) Region 1 er blevet enig om en teknisk anbefaling til S-meter kalibrering til HF og VHF/UHF transceivere i 1981.^[3]^[4]

IARU Region 1 teknisk anbefaling R.1 definerer S9 under eller lig 30MHz (HF-bånd) til at være en modtager indgangseffekt på -73 dBm.^[3] Det svarer til en RMS-spænding på 50 mikrovolt på modtagerens antenneindgang under antagelse af, at modtagerens indgangsimpedansen belaster med 50 ohm.

For højere frekvenser end 30MHz (fx VHF-bånd) er anbefalingen, at S9 svarer til modtager indgangseffekt på -93 dBm.^[3] Dette er ækvivalent med 5 mikrovolt RMS over 50 ohm.

Anbefalingen definerer en forskel på én S-enhed til at være en forskel på 6 decibel (dB), ækvivalent til en spændingsforhold på to - eller et effektforhold på fire.^[3]

Signaler stærkere end S9 angives med en tillægs dB værdi, f.eks. "S9 + 20dB", eller verbalt, "20 decibel over S9" eller simplere "20 over 9".^[3]

Eksempler

**Korresponderende LB/MB/HF (30MHz >= f)**
S signalstyrke	μV (50 Ω)	dBm	dBμV (50 Ω)	Watt
S9	50,2	-73	+34	50 pW
S8	25,1	-79	+28	12,5 p W
S7	12,6	-85	+22	3,16 p W
S6	6,3	-91	+16	794 f W
S5	3,2	-97	+10	200 f W
S4	1,6	-103	+4	50 f W
S3	0,8	-109	-2	12,6 f W
S2	0,4	-115	-8	3,16 f W
S1	0,2	-121	-14	794 a W

**Korresponderende VHF/UHF (f > 30MHz)**
S signalstyrke	μV (50 Ω)	dBm	dBμV (50 Ω)	Watt
S9	5,0	-93	+14	500 f W
S8	2,5	-99	+8	125 f W
S7	1,26	-105	+2	31,6 f W
S6	0,63	-111	-4	7,94 f W
S5	0,32	-117	-10	2 f W
S4	0,16	-123	-16	500 a W
S3	0,08	-129	-22	126 a W
S2	0,04	-135	-28	31,6 a W
S1	0,02	-141	-34	7,94 a W

Nøjagtighed

De fleste S-metre er ikke kalibrerede efter IARU Region 1 tekniske anbefaling R.1 og kan i praksis kun anvendes som et relativt mål af signalstyrken, baseret på modtagerens AGC spænding. Nogle S-metre er kalibreret til at kunne aflæse S9 for en indgangsspænding på -73 dBm, men har ikke de korrekte 6 dB per korresponderende S-enhed.^[5]

Ofte er korrelationen mellem en radiolytters kvalitative signalstyrke indtryk og den aktuelle signalstyrke ringe, fordi modtagerens AGC holder lydudgangens styrke forholdsvis konstant, på trods af ændringer i indgangssignalstyrken.

Se også

Indikatorrør

Kilder/referencer

^ encyclopedia2.thefreedictionary.com: S meter, backup
^ rfcafe.com: April 1966 Popular Electronics: Confused About S-Units? Citat: "...Each S−level step indicated a signal decrease of 5 to 6 dB below the previous S−level, again depending on the manufacturer's preference. As you might expect, confusion ensued. Nowadays there is an unofficial but generally adopted definition of S9 through S1, beginning at -73 dBm for S9, and then a 6−dB step size down to S1 level of (8 x −6 dB = −48 dB) = −121 dBm. It applies across the specified receive band(s), independent of frequency. Author Marshall Lincoln reviews S-units and S-meter circuits...An important variable which causes S-meter reports to be inconsistent is the fact that receiver manufacturers do not have a common calibration standard. Also, each manufacturer has his own calibration method...", backup
^ ^a ^b ^c ^d ^e
www.iaru-r1.org: IARU-R1 VHF Handbook. Version 9.01 March 2021 Citat: "...[page 115] IARU Region 1 Technical Recommendation S-METER READINGS. BRIGHTON 1981, TORREMOLINOS 1990. Standardisation of S-meter readings
- One S-unit corresponds to a signal level difference of 6 dB,
- On the bands below 30 MHz a meter deviation of S-9 corresponds to an available power of -73 dBm from a continuous wave signal generator connected to the receiver input terminals,
- On the bands above 30 MHz this available power shall be -93 dBm,
- The metering system shall be based on quasi-peak detection with an attack time of 10 msec +- 2 msec and a decay time constant of at least 500 msec. ...", backup
^ International Amateur Radio Union Region I (1981). IARU Region 1 Technical Recommendation R.1. Brighton, England, UK.
^ Measurements of amateur radio transceiver S Meter calibrations

Eksterne henvisninger

giangrandi.ch: S-meter and signal strength

[1] yclopedia2.thefreedictionary.com: S meter, backup

[2] rfcafe.com: April 1966 Popular Electronics: Confused About S-Units? Citat: "...Each S−level step indicated a signal decrease of 5 to 6 dB below the previous S−level, again depending on the manufacturer's preference. As you might expect, confusion ensued. Nowadays there is an unofficial but generally adopted definition of S9 through S1, beginning at -73 dBm for S9, and then a 6−dB step size down to S1 level of (8 x −6 dB = −48 dB) = −121 dBm. It applies across the specified receive band(s), independent of frequency. Author Marshall Lincoln reviews S-units and S-meter circuits...An important variable which causes S-meter reports to be inconsistent is the fact that receiver manufacturers do not have a common calibration standard. Also, each manufacturer has his own calibration method...", backup

[iaru_standard-3] www.iaru-r1.org: IARU-R1 VHF Handbook. Version 9.01 March 2021 Citat: "...[page 115] IARU Region 1 Technical Recommendation S-METER READINGS. BRIGHTON 1981, TORREMOLINOS 1990. Standardisation of S-meter readings
One S-unit corresponds to a signal level difference of 6 dB,

On the bands below 30 MHz a meter deviation of S-9 corresponds to an available power of -73 dBm from a continuous wave signal generator connected to the receiver input terminals,

On the bands above 30 MHz this available power shall be -93 dBm,

The metering system shall be based on quasi-peak detection with an attack time of 10 msec +- 2 msec and a decay time constant of at least 500 msec. ...", backup

[4] One S-unit corresponds to a signal level difference of 6 dB,

[5] On the bands below 30 MHz a meter deviation of S-9 corresponds to an available power of -73 dBm from a continuous wave signal generator connected to the receiver input terminals,

[6] On the bands above 30 MHz this available power shall be -93 dBm,

[7] The metering system shall be based on quasi-peak detection with an attack time of 10 msec +- 2 msec and a decay time constant of at least 500 msec. ...", backup

[iaru_standard2-4] International Amateur Radio Union Region I (1981). IARU Region 1 Technical Recommendation R.1. Brighton, England, UK.

[5] Measurements of amateur radio transceiver S Meter calibrations

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