RSN beats RST for signal reports in amateur radio

By Neil ZL1NZ

Most radio amateurs are familiar with the RST system of signal reports on CW – or the simpler RS version on voice modes.

RST has been around for almost a century and it’s showing its age. I believe it’s time for an upgrade to a more useful system called RSN.

RSN is easy to learn and use because it is quite similar to RST, except that it discards the Tone report in favour of the much more helpful Noise figure.

Let’s take a look at both systems, as well as a couple of others that are occasionally heard on the air.

Let me know what you think. Is it time to ditch RST in favour of RSN? Many of us already have! 🙂

1. RSN

RSN is an attempt to provide a more useful signal report than the more commonly used RST. It’s not perfect, but I think it’s a significant improvement and a system that all amateurs ought to consider.

RSN uses three numbers, as follows:

Readability

1–Unreadable

2–Barely readable, occasional words distinguishable.

3–Readable with considerable difficulty.

4–Readable with practically no difficulty.

5–Perfectly readable.

Signal strength

1-9, based on S-meter reading.

Noise strength

1-9, based on S-meter reading.

If there is a chirp, the letter C may be added.
If there are key clicks, add K.

RSN was developed by Lou VK5EEE and Tim VK3IM in 2019 and is now used routinely on NZ Net and VKCW Net.

One of the problems with RST (Readability, Signal strength, Tone) is that the T is virtually obsolete. It is extremely rare nowadays to hear any signal that is less than T9. And if the tone is bad, we can report it in other ways.

But we do have big problems these days with noise, so that’s what the N in RSN is for.

To use RSN simply note the S-meter reading with no signals. This is your noise level, N. It’s not likely going to change much during any on-air session, but if it does you just update the number. When noting my Noise level, I do not consider short bursts of static, only the relatively constant background noise.

For example: if my noise level is strength 2, then I might give another station a signal report of “RSN 592”. Or, if I tell another station they are “RSN 455”, they will understand that although their signal strength is OK, it’s the same level as my noise, hence readability is only 4.

There are some challenges with using RSN:

1. If the signal is weak, it can be hard to know its strength because the S-meter is responding to the noise level (RST has the same limitation though). In such cases I estimate the signal strength, based on how well I’m hearing it through the noise. Even on stronger signals, most experienced operators can estimate the signal strength without consulting a meter.

2. Filter settings will change the noise level dramatically, so which is the right noise level to report? I feel we should use the noise level we are working with. If my filter is set to 1 kHz I may have a noise level of strength 6 on 80 or 40 metres. With a 400 Hz filter it could drop to strength 3, and with a 150 Hz filter (my preferred filter for CW) it will likely be strength 1 or strength 2. The Signal strength, however, will be unchanged, at least on modern rigs with minimal loss in the filters. So my report will be “RSN 572”, for example.

3. What do we do if a station has poor tone? If appropriate, use the C or K suffix described above. Or, if necessary, simply revert to the old system, and send it like this “RST 596”. I suspect very few ops know what the Tone numbers mean, so you’ll probably need to spell it out anyway. 🙂

Bonus: Unlike RST, RSN is not limited to use on CW. It can be used just as effectively on voice modes too.

2. RST

Introduced in the 1930s, the RST system remains the most commonly used system of signal reporting among radio amateurs, mainly due to inertia, I believe. The T (Tone) number is largely irrelevant nowadays as most modern transmitters have excellent tone.

Readability

1–Unreadable

2–Barely readable, occasional words distinguishable.

3–Readable with considerable difficulty.

4–Readable with practically no difficulty.

5–Perfectly readable.

Signal Strength

1–Faint signals, barely perceptible.

2–Very weak signals.

3–Weak signals.

4–Fair signals.

5–Fairly good signals.

6–Good signals.

7–Moderately strong signals.

8–Strong signals.

9–Extremely strong signals.

Tone

1–Sixty cycle a.c or less, very rough and broad.

2–Very rough a.c., very harsh and broad.

3–Rough a.c. tone, rectified but not filtered.

4–Rough note, some trace of filtering.

5–Filtered rectified a.c. but strongly ripple-modulated.

6–Filtered tone, definite trace of ripple modulation.

7–Near pure tone, trace of ripple modulation.

8–Near perfect tone, slight trace of modulation.

9–Perfect tone, no trace of ripple or modulation of any kind.

If there is a chirp, the letter C may be added.
If there are key clicks, add K.
If the signal is as steady as crystal control, add the letter X to the RST report.

3. QRK/QSA

This is the format that was used in the maritime radio service. QRK is Readability and QSA is Signal Strength, and both are on a scale of 1 to 5. So a perfect signal is “QRK5 QSA5”. Here are the definitions:

QRK#: Your intelligibility (or that of …) is
1 (bad)
2 (poor)
3 (fair)
4 (good)
5 (excellent)

QSA#: The strength of your signals (or those of …) is
1 (scarcely perceptible)
2 (weak)
3 (fairly good)
4 (good)
5 (very good)

4. Q#

A shorter form of QRK is just Q#, ranging from Q1 (if unreadable) up to Q5 (perfect copy).