VK5HW AR musings

Or why a 59 report is really meaningless!

A NOTE first: I've labeled this SNLR (Signal to Noise-Level Ratio) so as not to step on our purists feet. We could just call it SNR as it really a basic form, in an Amateur Way, of Signal to Noise Ratio.

Receiving an S9 signal doesn't automatically mean that the signal is clear and intelligible. The S-meter (or signal strength meter) gives us a snapshot of the signal strength, but it doesn't tell us anything about the Noise Level (NL) or the Signal to Noise-Level Ratio (SNLR), which are crucial in understanding the overall quality of the received signal. A signal might be strong in terms of the S-meter, but if the noise level is similarly high, then the actual communication may be difficult or unclear. Most of today's operators will add an Audio quality report of 5, to make the report 59 which in amateur jargon means that the received transmission supposed to be of excellent quality e.g., an excellent signal. However, to often we hear stations giving a report of 59 or even 59+ only to go on to request a retransmission. Audio quality reports have a scale from 1 to 5 and are given by the operator. With 5 being excellent and 1 being very poor. This relies heavily on the operators HSP, and as we all have experienced, those "Audio reports are ...." well let's say that those reports are not very reliable.

For instance, if the noise level at the receiving station is S8, and the received signal is S9, the SNLR would only be 6 dB. Which would mean that the signal is just slightly stronger than the noise. This could make understanding the transmission challenging, even if it shows up as S9 on the meter. On the other hand, if the noise level is low (say S3) then an S9 signal would be much clearer.

The Importance of SNLR

SNLR (Signal to Noise-Level Ratio) gives us a much better sense of how usable a signal is as it compares the strength of the desired signal to the current background noise. A high SNLR means that the signal is much stronger than the noise, making it easier to decode and work with. On the other hand, a low SNLR means the noise is almost as strong or stronger than the signal, which can lead to poor communication quality or to a completely unreadable signal.

To calculate the SNLR we need two signals, the noise level and the signal strength of the received transmission, both numbers need to be a power level (dB). And since the levels will be rather small we'll use the Decibel in milli Watts e.g, in dBm.

Determining the Noise Level

Determining the Noise Level (NL) of our receiving system is rather easy, all we have to do is tune to a channel where no signal is present and record the S-Value (for instance, S4 as in my case).

Next we tune to a channel with a transmission and from the below we can see I've tune to a station which has an S9+10 average signal level.

Converting S-Values to Power

From the IARU Technical Recommendation R.1:

S1 corresponds to -121 dBm
S9 corresponds to -73 dBm

And the steps between S-Units are in 6 dB increments. This means:

S1 to S2 = -121 dBm to -115 dBm (6 dB increase)

Above S9 we tend to add a dB value to the S9 value, i.e.

S9 to S9+10 = -73 dBm to -63 dBm (10 dB increase)

click to view larger file

So, to calculate the SNLR:

Convert both the received signal strength and the noise level into power levels (dBm).
Calculate the difference between the received signal and the noise level (e.g., SNLR = Signal Power - Noise Level).

Using the above values:

Using the above graph we convert the received noise level of S4 to a power level of -103dBm and the received signal level of S9+10 to -63dBm.

Using the below formula:

SNLRdB = (Signal-LeveldBm) - (Noise-LeveldBm)

SNLR = (-63) - (-103)

SNLR = 40 dB

This would mean that the signal is 40 dB above the noise level, which is a strong signal and would be very clear.

Conversely, if the received signal would be S9 (-73 dBm) and the noise level would be S6 (-91 dBm), the SNLR would only be 18 dB.

While still a reasonable SNLR, it would be somewhat noisier than the 9+10 example, and we might find that we would need to ask for a repeat transmission occasionally.

Potential Benefits of Using SNLR instead of S-Meter Values

More Accurate Representation of Signal Quality:

SNLR considers both the signal strength and the noise level, which gives a much clearer idea of the actual quality of the communication link.

Increased Context:

By reporting SNLR, operators would have more information about whether the signal is being received clearly or if noise is impacting communication.

Noise Awareness:

Instead of just reporting an S9 signal, one could be aware of how much noise is present at the receiving station. This could help with adjusting the transmitting stations output power, e.g. increasing the output from 100W to 400W, a power level increase of 6dB should in principal add 6dB to the SNLR. Remember bigger SNLR = better signal quality.

Challenges

SNLR requires additional measurements:

To report SNLR, operators would need to be able to measure or estimate the Noise Level (NL) at their location. This can be challenging if the equipment doesn't provide this information directly. Most modern SDR systems do have the ability to read signal strength as a power or voltage level.

S-meter and SNLR are still subjective:

While SNLR is definitely more meaningful than just reporting an S-value, it still depends on the equipment's ability to measure signal strength and noise level accurately. Again, most SDR systems are very accurate.

Conclusion

Reporting 59 without any context of the noise level or SNLR doesn't provide the full picture. Shifting to SNLR as a primary metric would give operators a much better understanding of the quality of the received signal. It would not only account for the signal strength but also how well the signal stands out from the noise in the environment, leading to clearer communication and fewer misunderstandings.

Incorporating SNLR reports into amateur radio communication could definitely improve clarity and signal quality perception. Perhaps this is something more operators could adopt in their day-to-day operations.

Most SDR (Software Defined Radio) already have the ability to report the signal strength as a power or voltage level. A few lines of code and the SNLR could additionally be displayed.

Appendix

SNLR Table

NL S3 NL S4 NL S5 NL S6 NL S7 NL S8 NL S9
S SNLR SNLR SNLR SNLR SNLR SNLR SNLR
1 -12 dB -18 dB -24 dB -30 dB -36 dB -42 dB -48 dB
1.5 -9 dB -15 dB -21 dB -27 dB -33 dB -39 dB -45 dB
2 -6 dB -12 dB -18 dB -24 dB -30 dB -36 dB -42 dB
2.5 -3 dB -9 dB -15 dB -21 dB -27 dB -33 dB -39 dB
3 dB -6 dB -12 dB -18 dB -24 dB -30 dB -36 dB
3.5 3 dB -3 dB -9 dB -15 dB -21 dB -27 dB -33 dB
4 6 dB dB -6 dB -12 dB -18 dB -24 dB -30 dB
4.5 9 dB 3 dB -3 dB -9 dB -15 dB -21 dB -27 dB
5 12 dB 6 dB dB -6 dB -12 dB -18 dB -24 dB
5.5 15 dB 9 dB 3 dB -3 dB -9 dB -15 dB -21 dB
6 18 dB 12 dB 6 dB dB -6 dB -12 dB -18 dB
6.5 21 dB 15 dB 9 dB 3 dB -3 dB -9 dB -15 dB
7 24 dB 18 dB 12 dB 6 dB dB -6 dB -12 dB
7.5 27 dB 21 dB 15 dB 9 dB 3 dB -3 dB -9 dB
8 30 dB 24 dB 18 dB 12 dB 6 dB dB -6 dB
8.5 33 dB 27 dB 21 dB 15 dB 9 dB 3 dB -3 dB
9 36 dB 30 dB 24 dB 18 dB 12 dB 6 dB dB
9+3 39 dB 33 dB 27 dB 21 dB 15 dB 9 dB 3 dB
9+6 42 dB 36 dB 30 dB 24 dB 18 dB 12 dB 6 dB
9+10 46 dB 40 dB 34 dB 28 dB 22 dB 16 dB 10 dB
9+12 48 dB 42 dB 36 dB 30 dB 24 dB 18 dB 12 dB
9+15 51 dB 45 dB 39 dB 33 dB 27 dB 21 dB 15 dB
9+18 54 dB 48 dB 42 dB 36 dB 30 dB 24 dB 18 dB
9+20 56 dB 50 dB 44 dB 38 dB 32 dB 26 dB 20 dB
9+25 61 dB 55 dB 49 dB 43 dB 37 dB 31 dB 25 dB
9+30 66 dB 60 dB 54 dB 48 dB 42 dB 36 dB 30 dB
9+35 71 dB 65 dB 59 dB 53 dB 47 dB 41 dB 35 dB
9+40 76 dB 70 dB 64 dB 58 dB 52 dB 46 dB 40 dB
9+45 81 dB 75 dB 69 dB 63 dB 57 dB 51 dB 45 dB
9+50 86 dB 80 dB 74 dB 68 dB 62 dB 56 dB 50 dB
9+55 91 dB 85 dB 79 dB 73 dB 67 dB 61 dB 55 dB
9+60 96 dB 90 dB 84 dB 78 dB 72 dB 66 dB 60 dB

HSP = Human Signal Processor (normally found between the ears)