VHF/UHF S-meter
IARU Region 1
recommendation defines S9
for VHF/UHF to be a receiver input power of -93 dBm.
This is the equivalent
of 5 µV in 50 Ω. Again, one S-unit corresponds to a difference of 6 dB,
equivalent to a voltage ratio of two, or a power ratio of four.
|
Conversion between power and VHF/UHF S-units |
|
S-reading |
Pin @50Ω |
Vin @50Ω |
[dB
above1µV]Vout[1µV] @50Ω |
|
S9 + 40 dB |
-53 dBm |
0.50 mV |
54 dBµV |
|
S9 + 30 dB |
-63 dBm |
0.16 mV |
44 dBµV |
|
S9 + 20 dB |
-73 dBm |
50 µV |
34 dBµV |
|
S9 + 10 dB |
-83 dBm |
16 µV |
24 dBµV |
|
S9 |
-93 dBm |
5.0 µV |
14 dBµV |
|
S8 |
-99 dBm |
2.5 µV |
8 dBµV |
|
S7 |
-105 dBm |
1.26 µV |
2 dBµV |
|
S6 |
-111 dBm |
630 nV |
-4 dBµV |
|
S5 |
-117 dBm |
320 nV |
-10 dBµV |
|
S4 |
-123 dBm |
160 nV |
-16 dBµV |
|
S3 |
-129 dBm |
80 nV |
-22 dBµV |
|
S2 |
-135 dBm |
40 nV |
-28 dBµV |
|
S1 |
-141 dBm |
20 nV |
-34 dBµV |
HF S-meter
Many amateur radio and
shortwave broadcast receivers feature a signal strength meter (S‑meter).4
In 1981, the International
Amateur Radio Union (IARU) Region 1 agreed on a technical
recommendation for S‑meter calibration
of HF and VHF/UHF transceivers.5,6
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 µV at
the receiver’s antenna input assuming the input impedance
of the receiver is 50 Ω.
The recommendation
defines a difference
of one S-unit corresponds to a difference of 6 dB,
equivalent to a voltage ratio of two, or a power ratio of four. Signals
stronger than S9 are given with
an additional dB rating, thus “S9 + 20 dB”, or, verbally, “20 decibel over
S9”, or simply “20 over 9”
or even the simpler “20 over.”
Well-designed S-meter on the DRS WJ-8711A HF transceiver. Source: N9EWO
|
Conversion between power and HF S-units |
|
S-reading |
Pout @50Ω |
Vin @50Ω |
[dB
above1µV]Vout[1µV] @50Ω |
|
S9 + 40 dB |
-33 dBm |
5.0 mV |
74 dBµV |
|
S9 + 30 dB |
-43 dBm |
1.6 mV |
64 dBµV |
|
S9 + 20 dB |
-53 dBm |
0.50 mV |
54 dBµV |
|
S9 + 10 dB |
-63 dBm |
0.16 mV |
44 dBµV |
|
S9 |
-73 dBm |
50 µV |
34 dBµV |
|
S8 |
-79 dBm |
25 µV |
28 dBµV |
|
S7 |
-85 dBm |
12.6 µV |
22 dBµV |
|
S6 |
-91 dBm |
6.3 µV |
16 dBµV |
|
S5 |
-97 dBm |
3.2 µV |
10 dBµV |
|
S4 |
-103 dBm |
1.6 µV |
4 dBµV |
|
S3 |
-109 dBm |
800 nV |
-2 dBµV |
|
S2 |
-115 dBm |
400 nV |
-8 dBµV |
|
S1 |
-121 dBm |
200 nV |
-14 dBµV |
source:
https://hamwaves.com/decibel/en/ |