In the realm of radio communications, the party at each end usually wants to know the quality of their signal and vice versa so they can use it to adjustment their:
What does signal strength really mean?
The earliest qualitative metrics involved a simple numerical scale, usually 1-9 scale, for the "strength" of the signal. Right away, you can see the problem. What does "strength" really mean? The receiving party usually doesn't know the output power of the transmitter and, even if they did, their only measurable quality is the strength of what they receive and that's affected by the transmitter's power, antenna type, direction, band conditions, time of day, frequency, noise interference, solar wind, and the receiver's antenna, receiver circuity, and much more.
So, a signal strength figure, on its own, is next to meaningless. Case in point: At the time of this writing, my Inverted V antenna failed and went out of commission so I literally tossed a 12 foot piece of rusty speaker wire horizontally to a nearby bush just before we got hit with several major snow storms. That poor excuse for a wire even sagged till its center was on the snow or a few feet above the ground. Despite that, I was able to QSO with Battle Creek Michigan from the Boston area, Saint-Maarten Islands, Turks and Cacos Islands, Virginia, and Florida. No doubt most were running directional beams on towers with 1kw linears so they appeared to me as being at maximum strength when in reality, my rusty wire could not tell what their actual strength was here - other than knowing they were pumping a lot of power.
Adding Metrics to the report:
With those transmit power issues in mind, signal reports added additional metrics such as intelligibility. The most common form of that is the currently popular HAM standard of Readability (1-5) followed by Signal strength (1-9) making up the so-called RS standard. So, a "59" report is the maximum quality of totally readable with maximum strength. However, strength is still an issue. A strong signal could be anything from S6 to S9 to S9+10-40db above. As such, you'll often hear "You're 59 at S9+10db". Again, that is how the receiver perceives the signal.
The RS standard has an older cousin called the RST that is/was used by CW operators to add the quality or Tone of the CW carrier signal where the worst case "1" is a raspy, AC hum like signal and the best "9" being a a pure and well modulated tone.Again, that is not what it seems since the "tone" is a product of the receiver converting the carrier to a tone. However, there are rarer and more inefficient CW modes where a true audio tone is transmitted as SSB or AM.
In CW operation, individual digits may be abbreviated by substituting as follows: 1 = A, 2 = U, 3 = V, 4 = 4, 5 = E, 6 = 6, 7 = B, 8 = D, 9 = N, 0 = T (for instance, RST 599 could be sent as 5NN - a shorter message in CW). These are referred to as "cut numbers" and are obtained by replacing all of the dashes in a CW digit with a single dash. Cut numbers are not suitable for transmitting data which already contains mixed alphanumeric code, such as call signs.
The RSQ method was then added for other digital modes of transmission such as like PSK31.
An RSV (SSTV) rating system for Slow Scan TV further complicates things:
Then there's the RSV (ATV) rating for Fast Scan TV where video quality is replaced by a 6-level code describing the signal-to-noise ratio of the video with these values:
- P0 - all image detail lost
- P1 - 3-8dB, barely legible
- P2 - 8-20dB, definitely noisy
- P3 - 20-35dB, somewhat noisy
- P4 - 35-45dB, slightly noisy
- P5 - 45dB+, no discernible noise
Pro broadcasters and operators need more info.
International broadcaster needed a more definitive rating system which the ITU formalized as two metric reporting systems of 5 and 8 digits, respectively. Each digit has a uniform value range of 1-5 where 5 is the best and 1 is the worst or unusable. A 5-level range was chosen based on the fact that finer detail was of no value due to differences in perception, understanding, consistency, diligence, and the sheer number of other factors that cannot be accounted for in 5 or, even, 8 codes.
SINPO: This 5-digit rating stands for Signal Interference Noise Propagation and Overall.
SINPFEMO: Since broadcasters are especially interested in fading and modulation quality, 3 digits "FEM" were added to made a 8-digit rating whose attributes are codes where FEM codes refer to Frequency of propagation fading plus the Excellence and depth of Modulation.
RS needs some therapy.
In light of the rampant misuse of the RS "59" code system, I'm happy to hear some operators reporting to the more complete and legible SINPO code. I have no problem with the full SINPFEMO code since it provides so much more meaningful data. But, it's certainly conversational and can be relegated to logging and comments.
I've used the SINPO code for decades dealing with professional broadcasters and find it VERY helpful and hard to abuse. Even the laziest of us should be ashamed to routinely say you're all 5s when, in fact, that would be extremely rare.
Something better? For my part, I've starting logging my QSL's with a comment containing an RS/SINPO code in the hope it will encourage others to do the same in the interest of reporting qualities the other operator can actually use to improve their settings.
Why do I still report RS? Because QSL confirmations might be rejected if you don't record the RS "59" code you were given during the QSO.
Is it so bad? I can hear some grumbling, "Yeah? Right! 5 digits?" But, consider this: When you really think it through, SINPO can be almost as fast as produce (if not faster) as a composing a truly valid RS rating. Why? Because, to produce a true RS rating, you have to stop and think in terms of 2 different scales. R(1-5) and S(1-9). I don't know about you, but my brain has to pause to think about using 2 different scales for 2 adjacent digits.
For example, Jack and Jill are in a QSO. Jack wants to convey, log, or both, Jill's transmission quality. He thinks her readability was sort of 2/3 of "best" and her signal strength was fairly weak - about 1/3 of best.
OK, so her "R" was (ah, 1-5, so 2/3 is a 3 or a 4? Her signal was weak so that's, hmm, 1-9, ok, about a 3, no, 4? OK, I'll go with an RS of "33"? I suspect that Jill (and most other operators) would do a double take on a "33" RS report because: (a) most operators just always say "59" or "58" and (b) it's as much trouble to decode quickly as it was encode it. Hmm. "3". That's low, well, actually, out of 5, that's not too bad. And my signal was 3? Oh, yeah, that's out of 10, so that's pretty weak.
Because of RS rating quirks, the memorable acronym of SINPO, and the ease of always thinking 1-5 where 1 is worst and 5 is best, I find composing a SINPO just as fast and FAR more meaningful.
Also consider that when 2 operators chat a bit to really convey their mutual transmission qualities, they'll very often say things to the effect of , "Hey, Jill, ..."
"... your signal was quite strong, +10db" ... that's the "S", so 5.
"... another signal was trampling you" ... that's the "I", so a 2 or 3.
"... the band was really noisy tonight" ... that's the "N", so a 2.
"... boy, your signal was popping in and out" ... that's the "P", so a 3.
"... But, overall, I could make you out quite well" ... that's the "O", so a 4.
So, the SINPO rating is 5-3-2-3-4. That's a lot of great info.
I have no allusions. I've already been hearing "Your all 5's" a bit too often. That can, indeed, be true if you're in the path of 1,500 watts fired through a 4 elements beam and picked up by any decent antenna. I thin those that resort to such expediencies should just as well say, I hear you really well and not mangle a rating system with false reductions.
I totally concur that SINPFEMO is not feasible for fast-paced DX contests or even in general QSO conversation. But it has its place in a proper and detailed logging. So, SINPO works for most fast pace QSLing and takes all of 5 seconds while it may take 20 minutes make it through a log jam.
At least give it a thought. If you are joined at the hip to RS, then, at least report it correctly. It's really a drag to hear 59 for everything which makes it nothing more than "I read you OK!".
Hope this was food for though and helps add accuracy to transmission reporting.