What is meant by the "S"ignal reception codes? (S1, S6, S9+30dB, etc)

[pianoplayer88key]

So what is meant by those codes? I'm thinking the scale I use is different than everyone else's, cause I only have been using S1 to S9, and it was only relatively recently (within the past couple years or so) I even heard of people using S9+XdB...
Examples of what I've used them as would be:
S1 - barely detectable carrier, rapid fade (beat with another co-channel station whose frequency isn't quite exactly synchronized), weak mumbling audio (where you don't hear everything clearly enough to understand, for example "All ne----------he time. Th-------------le-you bee n-------------ghty. You giv-----------ty-two min--------------ve you---------rld." (All News, all the time. This is KFWB News 980. You give us 22 minutes, we'll give you the world.)), etc.
S2 - weakest signal where you can hear every word clearly enough to understand
~S4 - approximate threshold for lighting tuning indicator on a radio, or stopping the auto seek
~S5 - easily listenable signal with mild to semi-moderate static - like listening to a 50kW station at ~1000kHz from ~100 miles with ground conductivity ~8-15.
S7 - signal strong enough to have full noise quieting in the receiver (for example listening to a talk station, radio would be silent (no static) in gaps between words/sentences)
S9 - signal so strong that it's strongly bleeding up and down several channels on your radio, and producing images/mixtures several hundred kHz removed from its assigned frequency
S10 - (not on "official" scale) you get badly distorted audio when you're tuned to its frequency because you're overloading your radio

But... I sometimes hear references of S9+60dB... and chances are my version of S9+20 or S9+30 dB would require you to have a wire connected directly from a 50kW station's transmitting antenna to the antenna terminal on the circuit board of your receiver.. so obviously my scale seems to be a bit different.... so what would be a properly-defined S1 to S9 to S9+60dB etc. scale?

 

[stormy01]

Yes, the scale varies from receiver to receiver - there is no standardization of "S-Units" among different manufacturers of receivers, it's relative from one receiver to the next. When someone mentions the higher values, like S9 + 30dB on a certain signal there are a number of variables: the receiver itself, the feedline, the antenna, the orientation of the antenna (if directional), the directional antenna versus an omnidirectional antenna, preamplifer, attenuator, antenna tuner, etc. So the higher readings are always widely variable, though the S1-S9 readings that you listed could be closer to the truth.

Check this article out online, this might offer some insight into "S-Codes" http://www.ac6v.com/sunit.htm

 

[w9wi]

...so what would be a properly-defined S1 to S9 to S9+60dB etc. scale?

In theory, S9 is 50uV at the antenna terminals of the receiver. Each S-unit is theoretically 6dB. (so S8 would be 25uV, S7 would be 12.5uV, etc...) S9+60dB would be 50 volts -- I suppose a direct connection to the 50kW transmitting antenna would be closer to S9+70dB but indeed your receiver is probably going to be literally on fire by the time you reach 50 volts on the input!

As "stormy01" says, most receivers don't match theory.

 

[radioman148]

...so what would be a properly-defined S1 to S9 to S9+60dB etc. scale?

In theory, S9 is 50uV at the antenna terminals of the receiver. Each S-unit is theoretically 6dB. (so S8 would be 25uV, S7 would be 12.5uV, etc...) S9+60dB would be 50 volts -- I suppose a direct connection to the 50kW transmitting antenna would be closer to S9+70dB but indeed your receiver is probably going to be literally on fire by the time you reach 50 volts on the input!

As "stormy01" says, most receivers don't match theory.

40 years ago when I used 11 meters, everytime you doubled your power you'd gain about an S unit on groundwave.
I don't know if that's applicable elsewhere.

 

[nd2023]

I have a signal strength meter on my portable radio, but it isn't in S units. I'm pretty good at estimating field strength based on that and how the signal behaves when I move around. I could give a good estimate of my distance from a city with a class B station, assuming no tropo.