S Meter
The S meter is supposed to represent a calibrated signal
strength of a received signal.
Most ham equipment manufactures have forgot this somewhere along the way, and have adjusted their S meters for more marketing purposes than anything.
The other thing that makes the S meter an inaccurate measurment device is that the S meter is driven by the AGC circuity in the receiver. This will cause them to not track with the 6db requirement of each S unit.
I like my S meters to be calibrated, as a know S meter reading is very meaningful to me. When I give a signal report I give the actual readings from my station.
I keep my S meters calibrated on my main two rigs in the shack. That being my Icom PCR-1000 receiver and my Kenwood TS-2000 transceiver. I use the following values to calibrate my S meters, and do not use the values necessarily published in the service manual.
One S unit is equal to change of 6dB in signal strength measured at the receiver input.
This corresponds to double the voltage or a four times power increase.
The IARU published a standard in 1981 for calibrated S meter values for HF and VHF
It basically states that
One S unit corresponds to a signal level difference of 6dB
It is measured from a continuous wave signal generator connected to the receiver input
On bands below 30 Mhz a meter deviation of S-9 corresponds to an available power of -73dBm f
On the bands above 144 mhz the 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.
I find it interesting that they left a hole between 30 and 144 Mhz, what should be do with 6 meters?
There is also reference in the ARRL handbook to the standard each S unit being 6db and a meter reading of S9=50uV which is -73dBm
So based on these two standards we come up with the following for HF
S-Units Micro dBm Relative Intensity
Volts S9 in dB
S1 0.2 -121 -48
S2 0.4 -115 -42
S3 0.79 -109 -36
S4 1.6 -103 -30
S5 3.2 -97 -24
S6 6.3 -91 -18
S7 13 -85 -12
S8 25 -79 -6
S9 50 -73 0
+10 160 -63 10
+20 500 -53 20
+30 1600 -43 30
+40 5000 -33 40
+50 16000 -23 50
+60 94000 -13 60
And the Following Table for VHF
S-Units Micro dBm Relative Intensity
Volts S9 in dB
S1 .0.2 -141 -48
S2 .04 -135 -42
S3 .079 -129 -36
S4 .16 -123 -30
S5 .32 -117 -24
S6 .63 -111 -18
S7 1.3 -105 -12
S8 2.5 -99 -6
S9 5 -93 0
+10 16 -83 10
+20 50 -73 20
+30 160 -63 30
+40 500 -53 40
+50 1600 -43 50
+60 9400 -33 60
What if I can not calibrate a meter to exactly match the above table?
I try to set the meter up so that S9 is accurate. That gives me a reference to go by.
On FM mobiles I do not even try to mess with the S meters in most cases. I have found them to be so inaccurate, that I have given up on trying to do much with them. If I am working on an alignment of a radio and there is an S Meter adjustment I try to set the S9 level if possible.
Most ham equipment manufactures have forgot this somewhere along the way, and have adjusted their S meters for more marketing purposes than anything.
The other thing that makes the S meter an inaccurate measurment device is that the S meter is driven by the AGC circuity in the receiver. This will cause them to not track with the 6db requirement of each S unit.
I like my S meters to be calibrated, as a know S meter reading is very meaningful to me. When I give a signal report I give the actual readings from my station.
I keep my S meters calibrated on my main two rigs in the shack. That being my Icom PCR-1000 receiver and my Kenwood TS-2000 transceiver. I use the following values to calibrate my S meters, and do not use the values necessarily published in the service manual.
One S unit is equal to change of 6dB in signal strength measured at the receiver input.
This corresponds to double the voltage or a four times power increase.
The IARU published a standard in 1981 for calibrated S meter values for HF and VHF
It basically states that
One S unit corresponds to a signal level difference of 6dB
It is measured from a continuous wave signal generator connected to the receiver input
On bands below 30 Mhz a meter deviation of S-9 corresponds to an available power of -73dBm f
On the bands above 144 mhz the 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.
I find it interesting that they left a hole between 30 and 144 Mhz, what should be do with 6 meters?
There is also reference in the ARRL handbook to the standard each S unit being 6db and a meter reading of S9=50uV which is -73dBm
So based on these two standards we come up with the following for HF
S-Units Micro dBm Relative Intensity
Volts S9 in dB
S1 0.2 -121 -48
S2 0.4 -115 -42
S3 0.79 -109 -36
S4 1.6 -103 -30
S5 3.2 -97 -24
S6 6.3 -91 -18
S7 13 -85 -12
S8 25 -79 -6
S9 50 -73 0
+10 160 -63 10
+20 500 -53 20
+30 1600 -43 30
+40 5000 -33 40
+50 16000 -23 50
+60 94000 -13 60
And the Following Table for VHF
S-Units Micro dBm Relative Intensity
Volts S9 in dB
S1 .0.2 -141 -48
S2 .04 -135 -42
S3 .079 -129 -36
S4 .16 -123 -30
S5 .32 -117 -24
S6 .63 -111 -18
S7 1.3 -105 -12
S8 2.5 -99 -6
S9 5 -93 0
+10 16 -83 10
+20 50 -73 20
+30 160 -63 30
+40 500 -53 40
+50 1600 -43 50
+60 9400 -33 60
What if I can not calibrate a meter to exactly match the above table?
I try to set the meter up so that S9 is accurate. That gives me a reference to go by.
On FM mobiles I do not even try to mess with the S meters in most cases. I have found them to be so inaccurate, that I have given up on trying to do much with them. If I am working on an alignment of a radio and there is an S Meter adjustment I try to set the S9 level if possible.
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