SNR, a better way to give a signal report

Or why I believe a 59 report is meaningless!

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 (SNR), 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 SNR 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 as the SNR is now 6x better i.e. 36dB vs 6dB. 

The Importance of SNR

SNR (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 SNR means that the signal is much stronger than the noise, making it easier to decode and work with. On the other hand, a low SNR 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 SNR 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, as shown in the below picture. 

Next we tune to a channel with a transmission and note the recived signal, say S9+10 as depicted below.

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 SNR:

1. Convert both, the received signal strength and the noise level into power levels (dBm).
2. Calculate the difference between the received signal and the noise level (e.g., SNR = 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:

 

SNRdB = (Signal-LeveldBm) - (Noise-LeveldBm) 

  

SNR = (-63) - (-103)

 

SNR = 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 S8 (-79 dBm), the SNR would only be 6 dB.

While still a reasonable SNR, 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 SNR instead of S-Meter Values

• More Accurate Representation of Signal Quality: 

SNR 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 SNR, 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 a 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, which is a power level increase of 6dB and as such should, in principal, add 6dB to the SNR.

 

Remember bigger SNR = better signal quality.

Challenges

• SNR requires additional measurements: 

To report SNR, 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 SNR are still subjective: 

While SNR 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 doesn't provide the full picture. Shifting to SNR 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 SNR 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 SNR could additionally be displayed.

Appendix

NOTE: The SNR changes with the receiver bandwidth however, for the purpose of a quality/signal report it is not nesseary to include the receiver bandwith. 

See https://vk5hw.blogspot.com/2022/02/lets-talk-about-receiving-signal-that.html

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

• IARU Technical Recommendation R.1
• Signal Level Strength Meter Calibration and IARU Standards
• Understand SINAD, ENOB, SNR, THD, THD + N, and SFDR so You Don't Get Lost in the Noise Floor 
• Signal strength and readability report
• Noise Counter-measures
• What is your S-Meter actually indicating
• S-Values are they useful
• A little history about S-Points
• How to achive receiver bliss

Excessive Single Side Band Transmission, also know as ESSB or eSSB.

There seems to be an increase in the transmit bandwidth range for SSB communications, which traditionally operates within a narrow-band of approximately 3 kHz. Now if we go with a 3 khz “Voice channel” for Single Side Band (SSB) then the Transmitted Bandwidth, let's call it the TxBW, should fit into the range 0-3000 kHz.

However, I’ve noticed more and more operators use a TxBW of 4 kHz or more. This is often referred to as Extended Single Side Band (ESSB) which I have seen to extend in some instances even to 5 kHz and more. The claim to fame is HiFi Audio.

Now Amateur Radio is an experimental hobby, so this, on the surface, shouldn’t irk anyone, shouldn’t it? However, I frequently encounter ESSB operators on 20 and 40m talking to operators who have not modified their station for ESSB communications, i.e. a station with a TxBW 5 kHz to a station with a 3 kHz Receiver Bandwidth, lets call that RxBW.

So what seems to be the issue?

Let's say a QSO is conducted on 14.229 MHz, one operator uses a TxBW of 2.9 khz and the other uses a TxBW of 2.4 kHz. Signal are good with about S7 both ways. Since this is conducted using the Upper Side Band and, if we apply a Voice Channel spectrum of 3 kHz the used frequency spectrum for that QSO is from 14.229 – 14.231 MHz (not quite but let's stick with 3 kHz). Stations operating on 14.232 MHz should not have any issues operating. However, let's assume one of the operators is operating at a TxBW of 5 kHz. This situation would infringe stations operating on 14.232 MHz quite badly. Another example would be if a DX station is calling on 14.232 MHz and I would like to work that station. However, I will be unable to do so due to the excessive TxBW of the ESSB operator (14.229 - 14.234 MHz). 

Anyone see an issue here? Well, I do! However, the question is does the ESSB operator see the issue? From my experience most ESSB operators do not.

So why use 5 kHz TxBW whilst conducting DX contacts. Aren't we trying to share the limited frequency spectrum between all Amateurs? There is certainly NO benefit to the station receiving the ESSB station. 

Frequency spectrum during “openings” are crowded and transmitting with a 5 kHz TxBW during these opening does not show any courteousey towards other spectrum users.

The above shows an Australian Operators transmission with a TxBW of  5 kHz and the DX station using a  less than 3 kHz “Voice Channel”. I will assume that the DX stations RxBW would not be more than it's TxBW.

NOTE: I’m referring to the TxBW and not the Intermodulation Products (IM) or “splatter”, e.g. the light blue “hair or whiskers” on either side of the signal, which are obvious related but are not discussed here.

This is even more frustrating on the 40m Band, as there are more an more local stations operating with a TxBW of greater than 4 kHz. 

Now Amateur Radio is an experimental hobby and experimenting with a TxBW > 3 kHz does fall under this category. So, yes I believe in experimenting but this is not experimenting, this is not understanding the implication of excessive TxBW. And believe me I’m all for experimenting. However, I am quite happy with a 2.4 kHz well balanced audio TxBW which would influence the use of an appropriate RxBW.

Additionally I believe that these operator would not know how much "real" power they are transmitting. If we talk about 400W PEP, then the average output power would be rather LOW.

NOTE: I also observed that these type of operators seem to drop their TxBW to 3 kHz during Contests!?!  Yet they seem to believe that during crowded DX sessions it is OK to use 5 kHz or more TxBW. Isn't that a bit hypocritical?

Since Amateur Radio is a self regulating hobby it might be about time to add a frequency spectrum for those inclined to use ESSB. I believe this has been done for certain other modulation schemes (AM/FM/DIGITAL).

Is my NOISE FLOOR (NF) really worse than yours ?

Well, let's answer that question first so you can move on to better things in life. And the answer is:

No it is not, because I use an S-Value indicator (S-Meter) that follows a Standard! The so called 6dB per S-Point (6dB/S) standard!

And that's it, 73 and catch you on the bands (as they say).

Oh, hello you are still here. So, it looks like you would like to know a bit more about this phenomena. Well, then read the below or maybe this "What is your S-Meter Really Displaying".

As far as I know, most Amateur Radios Transceivers from the three main manufactures, ICOM; YAESU and KENWOOD seem to display a 3dB/S scale below S9 (-73dBm). 

So if I read a Noise Floor (NF) of S3 on my S-Meter, which by using the 6dB/S standard would be -109dBm or -2.0dBμV NF.  And my QSO partner, i.e. you, is stating a NF of S2 which, using the applied 3dB/S scale would be a NF of -94dBm or -13dBμV.  

So is my NOISE FLOOR really worse than yours?

Let's have a look at the below two Tables, the left one is scaled in 6dB per S-Value i.e. my S-Meter and the right in 3dB per S-Value like your S-Meter. 

Received Power (Zin = 50 Ω)	Signal Strength S-Value 6dB step		Received Power (Zin = 50 Ω)	Signal Strength S-Value 3dB step
-121 dBm	1		-97 dBm	1
-115 dBm	2		-94 dBm	2
-109 dBm	3		-91 dBm	3
-103 dBm	4		-88 dBm	4
-97 dBm	5		-85 dBm	5
-91 dBm	6		-82 dBm	6
-85 dBm	7		-79 dBm	7
-79 dBm	8		-76 dBm	8
-73 dBm	9		-73 dBm	9

Doesn't that shed some light on this (issue)?

According to the IARU Handbook (Ver 9.0) Paragraph 4.1.3 S-Meter Standards:

1. One S-point corresponds to a level difference of 6dB.

2. On the bands below 30 MHz a meter deviation of S-9 correspond to an available power of a CW signal generator connected to the receiver input terminals, of -73dBm.

3. On the bands above 30 MHz a meter deviation of S-9 correspond to an available power of a CW signal generator connected to the receiver input terminals, of -93dBm.   

It has been a Standard for quite a while, but it seems that it has not been adapted widely.

Signal Level Strength Meter Calibration and IARU Standards

Listen to the Music

Listen to the music, but not on SSB with a 3kHz bandwidth. What I mean is, listen to the Amateur Radio Bands, and you will quickly understand what I'm talking about. Some of the audio signals on our bands are appalling. Even worse are some of the reports that people are relaying back to these poor operators.

It's worth noting that many amateur radio operators strive to have a clean and pleasant signal. However, both the amateur radio community and society, in general, have become non-constructive regarding any form of insights or criticism. Therefore, the information below may help some operators check their transmission quality.

A little bit of research on the internet reveals that the human voice contains frequencies ranging from about 100Hz to 8000Hz. However, only the energy between about 300Hz and 3800Hz contributes to the intelligibility of speech. Vocal content below 400Hz provides "body" to the voice, which is great for singers and radio announcers. Speech content above 3000Hz provides presence and can aid communication, to some extent. However, the added bandwidth can introduce noise and other complications.

In my opinion, in a Single Side Band (SSB) communication system, it's crucial to achieve the highest Signal-to-Noise Ratio (SNR) at the receiving station under strenuous propagation conditions to get the message across. To achieve this goal, we should transmit the portion of the human speech that affects articulation the most, which research has shown to be the spectrum between 300Hz and 3300Hz.

These bandwidth limits have been established in the days of long distance telephone systems and have served the telecom industry of our world quite well.

The standard SSB TX filter in most SSB transceivers is 2.7kHz wide, and a well-adjusted SSB transceiver has this filter aligned so that it will pass audio between 300Hz and 3000Hz. Since SSB transmitters are peak power-limited, transmitted energy below approximately 250 Hz will show power on the power meter but will not contribute to the articulation at the receiving station. However, these days we often see signals with a "power-grab" dominating the bands. Many operators focus solely on increasing their power output, resulting in signals that are difficult to copy and interfering with other spectrum users on either side of the selected channel. These bass-heavy signals can swamp the AGC in a receiver, creating a low-frequency rumble that is unintelligible and potentially causing issues for other spectrum users.

Fortunately, with the availability of publicly accessible Web-SDR systems, it's now possible to monitor one's own transmissions quite easily. 

The way I do this is however, slightly different as described below. 

To set up a transmission check, I first record a test transmission and play it back through the transceiver which is connected to a dummy load/antenna. While transmitting the recording, I listen to the signal using a second receiver (in my case, an SDR-IQ) to adjust the TX-audio profile, including the TX Bass and TX Treble on the ICOM, MIC gain, and compression.

When adjusting compression, I make sure to adjust the MIC gain so as to avoid the compressor pumping up background noise during speech breaks. By listening to my own transmission, I can tailor the audio characteristics to ensure that all transmitted power remains inside the available SSB channel. This is particularly important for QRP stations or foundation license holders, as losing just 3dB to either side of the channel means that only a quarter of the peak power is transmitted inside the wanted SSB channel, potentially making it difficult for the receiving station to copy the signal.

Below is a display of a test I conducted to get a more balanced audio profile. The LSB signal within the top of the waterfall in the below picture is showing emphasis on the low end of the audio spectrum. Visible on the bright red right hand area. Below this signal we can clearly see that I have selected/created a more balanced audio profile.

Analysing those signals, we can see that the first signal has quite a lot of emphasis on the lows, at around 100-400Hz (on the right the big red line). This makes the signal sound rather bassy, and although it shows a lot of power on the power meter, it is not overdriven (like most of the signals on the bands today). 

Operators who prefer to use wide-open audio filter might find this sounds okay. But for longer distances, were the receiving station only has a bit better than marginal reception, say S5, it would be difficult to copy.
The second signal shows much better-balanced audio and I would classify this as very good communication audio. However, the bandwidth of both signals is approximately 2.9kHz (100-3000Hz) which is still in the 3kHz channel bandwidth. I believe that the bottom signal would still sound rather nice at a 2.6, 2.4kHz bandwidth even in 2.1kHz with a lot less noise bandwidth this signal would still sound Q5.

Oh and ESSB enthusiast find my view of the use of narrow band audio for SSB harrowing. However, it would be nice if these OM's would find a space in our limited spectrum were they would NOT interfere with low power stations that they might not hear.

I've been seeing quite a few ESSB operators on 40m clobbering small signals due to their inability to hear those stations and make it difficult for others to make the contact with those stations. 

Also, I don't believe that ESSB should be used during a contest where bandwidth is limited, not even by a contest station.

S-Points, are they useful

The S-Meter in an Amateur Radio Receiver/Transceiver is an indicator for the received signal strength (Strength Meter). On HF, signal strength 9 (S9) has been defined to be an input power of -73dBm @ 50Ω (dBm is power expressed as decibels relative to 1mW). This is a level of 50µV (microvolts) measured at the antenna input port. And each step between S-Units corresponds to a difference of 6dB as recommended in the IARU Technical Recommendation R.1. 6dB is equivalent to a power ratio of four and a voltage ratio of two (S-Point History).

The term S-Unit/point is used to refer to the amount of signal strength that move the S-Meter indicator from one marking to the next, i.e. it moves by one S-Point/unit. On Amateur Radio equipment, most S-Meter markings are from S1 to S9, with marking above S9 in 10dB steps.

To be able to add meaning to the S-Meter report, I believe, Amateur Radio Operators should know how the S-Meter of the radio equipment is tracking against the IARU standard. Quite a few Amateur Radio Operators either don't seem to care or don't understand the value of having an instrument that can track precise. Let's consider the below;

• Profiling a couple of antennas by listening to the background noise.  On antenna one we see a noise level of S4 (-103dBm). Switching to the second antenna we see that the S-Meter indicates S6 (-91dBm). We could now conclude that there is a noise difference between ant1 and ant2 of 12dB or that one antenna has a gain of 12dB over the other.

• Checking the front to back ratio of a Beam (Yagi/Uda) Antenna. Receiving the signal from the front of the antenna the meter reads S9. Turning the antenna 180 degree, i.e. pointing the back of the beam to the signal source, the meter reads S5. This would indicate a nice 24dB(4 S-point = 4*6dB = 24dB) front to back ratio of the Antenna, but is it true?

• Comparing receiver prowess, i.e. using a receive splitter to split the receive signal equally to compare receivers. If receiver-1 is displaying S3 on the S-Meter and receiver-2 is displaying S7 on the same signal, is receiver-2 the better receiver?

We can clearly see that if we do not know how our S-Meter is tracking, i.e. are the steps between S-Points are really equal and at the 6dB step size. We can't be sure what is being displayed. Any of the above scenarios become guess work and as such would most likely lead us astray.

 

So to come back to the question at hand, I'd say since Amateur Radio is a Technical Hobby it would be nice to provide and receive a correct S-Value report, one that is trackable to a standard. An even better report would be SNR (one for the future).

However, if one uses the Radio for NET chats and contesting, then who cares if the S-value is S9 or S9+20dB or S5 for that matter.

Would it then not be more appropriate to say the quality of your signal at my station is Q5 or Q4, i.e. going back to the old Q(SA) system. One can always ask for an S-value, but what would be the usefulness in a value that does not track to a standard.