S Meter



Most ham equipment manufactures have forgoten this somewhere along the way, and have adjusted their S meters for more marketing purposes than anything.

Most people always give you a signal report os 599 anyhow right!!


I like my S meters to be calibrated, If I can not get the meter to track to reasonable reading I at least calibrate S9 to -73dBm

Most of these inaccuracies are caused by the S meter being driven by the receivers AGC circuity. Most if the time the AGC does not track with the 6db for each S unit.

In the HF receiver I am designing I am planning on implementing an S meter that is independent of the ACG to allow for a very accurate reading.




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.