Instead of a "Guess Meter" I have been looking at the S Meter Signals coming from my SDR Software. The 1st question out of the Cracker Jack Box is the accuracy of what is being seen. That also raises issues of any calibration and to what standard is being set for the measurements.
I have long felt that an S Meter was a crutch to be able to say to the station on the other end well you are hardly moving the needle. Or the most venerable and cherished response: "you are so strong you're pinning the meter". In reality there is only one measure, and it is binary! You are either being heard, a 1, or I can't hear you, a 0.
As with everything YMMV but unless calibrated and tested what you see on a panel meter or on a display is always suspect. That is why my binary approach may have some validity -- you are either a 1 or a 0!
TYGNYBNT.
73's
Pete N6QW
S Meters and 50dB/9
So just what are S Meter readings, and I must quickly add the reading is highly dependent on the antenna fitted to the radio. A world class radio connected to a 1-foot piece of wire may hear things but certainly lacks the accuracy and likely to miss that 100-milliwatt FT-8 station operating into a low hung dipole on Kingman Reef (KH5K prefix).
There is a basic underlying assumption and that is the antenna presents 50 Ohms to the receiver input. This sort of says at minimum it is an antenna cut for the band in use and has a 50 Ohm impedance.
(As found in Wikipedia)
The IARU had a recommendation to define a standard where an S9 signal is 50 microvolts (rms) at the input or -73dBm.
The recommendation further defines that 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. Thus, a 1-watt QRP signal that registers an S2 to jump to S3 would have to be like 4 watts. [10*log (4/1) = 6dB]
I used an Online Calculator to affirm 50.2uv (rms) = -73dBm resulting in an S9 report.
