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S METER
S meter (signal strength meter) a
quantitative measure of voltage of power presented at a
communications receivers.
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S units for frequencies below 30 MHz
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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
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-115
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-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
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-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
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1,22E-16
|
-129
|
-22,14
|
|
4
|
|
0,156
|
4,88E-16
|
-123
|
-16,12
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|
5
|
|
0,313
|
1,95E-15
|
-117
|
-10,10
|
|
6
|
|
0,625
|
7,81E-15
|
-111
|
-4,08
|
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7
|
|
1,25
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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
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-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
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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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last revised 05 May, 2025
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