That EUROPEAN vhf manual does contain this interesting insight on page 136http://www.9h1mrl.org/VHF_Handbook_V5_35.pdf
"8.6.1 SIGNAL REPORTING ( Recommendation R.1; R.2)
Although from the beginning of amateur radio signal reports have been essential, no formal standard for
the reports exists. But the "Readability, Strength, Tone" system with R,S and T values between 1 and 9 is
in widespread use. Several handbooks gave and give in words indications how the values are to be
The readability and tone reports are in principle "subjective" but the strength report can be objective as a
simple measurement of the received signal in voltage or power is possible. Such reports are in particular
at the VHF and higher frequencies useful for more precise evaluation of propagation, antenna properties
and receiver sensitivities.
At the IARU Region 1 Conference in Hungary 1978 the need for a harmonised standard for the "S-meter
scale" was expressed and a proposal was accepted for publication in society journals. The essential
recommendation was 1 S-point is 6 dB . At the Brighton Conference in 1981 the recommendation was
formally adopted as a standard for amateur radio equipment manufacturers.
At the 1990 Torremolinos conference an amendment was adopted which reconfirmed the -93 dBm
reference level for frequencies above 144 MHz, but no statement was issued for the bands between 30
and 144 MHz.
Although not explicitly stated the implication of the recommendation is that on VHF and higher frequencies
the S-meter will deviate on the thermal noise only ( S2 in 3 kHz bandwidth, S3 in 12 kHz bandwidth).
Although the recommendation is not too complex it seems to be rather difficult to implement by
Another matter is the Atone@ report. This is a subjective measure. It was important in the Aold
days@when rather primitive oscillators were used in the TX. Modern transmitters, even on the millimeter
bands, have in most cases a very good oscillator, resulting in a Apure tone@ and a T9 report is generally
given. On VHF and higher, however, the characteristics of the propgation medium can significantly
Amodulate@the signal ( doppler shift, spreading) and a T9 report is not possible. Definitions of tone
reports below 9 are rather vague. At the Region 1 conference 1999 in Lillehammer a recommendation
(R.2) has been accepted to use special letters for signal tone reports when the influence of the
propagation is detectable. Such reports can support propagation studies."