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S METER
S meter (signal strength meter) a quantitative measure of voltage of power presented at a communications receivers.

S units for frequencies below 30 MHz

S Reading uV (50Ω) P Watts dBm dB above 1uV
1 0,195 7,63E-16 -121 -14,19
2 0,391 3,05E-15 -115 -8,16
3 0,781 1,22E-14 -109 -2,14
4 1,56 4,88E-14 -103 3,88
5 3,13 1,95E-13 -97 9,90
6 6,25 7,81E-13 -91 15,92
7 12,5 3,13E-12 -85 21,94
8 25 1,25E-11 -79 27,96
9 50 5,00E-11 -73 33,98
9 +  10 160 5,12E-10 -63 44,08
9 +  20 500 5,00E-09 -53 53,98
9 +  30 1600 5,12E-08 -43 64,08
9 +  40 5000 5,00E-07 -33 73,98
9 +  50 16000 5,12E-06 -23 84,08
9 +  60 50000 5,00E-05 -13 93,98

 

S units for frequencies above 30 MHz

 
S Reading uV (50Ω) P Watts dBm dB above 1uV
1 0,0195 7,63E-18 -141 -34,19
2 0,0391 3,05E-17 -135 -28,16
3 0,0781 1,22E-16 -129 -22,14
4 0,156 4,88E-16 -123 -16,12
5 0,313 1,95E-15 -117 -10,10
6 0,625 7,81E-15 -111 -4,08
7 1,25 3,13E-14 -105 1,94
8 2,5 1,25E-13 -99 7,96
9 5 5,00E-13 -93 13,98
9 +  10 16 5,12E-12 -83 24,08
9 +  20 50 5,00E-11 -73 33,98
9 +  30 160 5,12E-10 -63 44,08
9 +  40 500 5,00E-09 -53 53,98
9 +  50 1600 5,12E-08 -43 64,08
9 +  60 5000 5,00E-07 -33 73,98

The International Amateur Radio Union (IARU) Region 1 agreed on a technical recommendation for S Meter calibration for HF and VHF/UHF transceivers in 1981.

IARU Region 1 Technical Recommendation R.1 defines S9 for the HF bands to be a receiver input power of -73 dBm. This is a level of 50 microvolts at the receiver's antenna input assuming the input impedance of the receiver is 50 ohms.

For VHF bands the recommendation defines S9 to be a receiver input power of -93 dBm. This is the equivalent of 5 microvolts in 50 ohms.

The recommendation defines a difference of one S-unit corresponds to a difference of 6 decibels (dB), equivalent to a voltage ratio of two, or power ratio of four.

Signals stronger than S9 are given with an additional dB rating, thus "S9 + 20dB", or, verbally, "20 decibels over S9" or simply "20 over 9".

 

Reference:

Wikipedia article based on IARU Region 1 Technical Recommendation R.1 http://en.wikipedia.org/wiki/S_meter

 

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Page last revised 07 April 2013  
 

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