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

ICOM IC-7610 S-Meter Tracking

Having been checking the S-Meter for my prefered software solutions  (SDR) I thought it might be a good time to also (re)check the S-Meter in my ICOM IC-7610. The setup is the same as for the previous two checks. Below is the result of my checks for my IC-7610. A quick graph of how well my ICOM IC-7610 S-Meter is tracking using the IARU Standard of 6dB steps (6dB/S-Unit).

Setup:

• Signal generator: XG3
• Level: -34.8dBm @ 13.8V
• Att: HP-355C & HP-355D (38dB for approx. -73dBm level)
• Frequency: 14.175MHz

Result:

Table 1

Graph 1

The graph shows a pretty linear S-Meter for the IC-7610 down to S4 with a 6dB step per S-unit. The above graph is based on the measurements at 14.175 MHz (20m) with the PreAmp off. However, enabling either preamp we can see from Table 1 that the measurements deviate quite a bit. So for the times that I'd use either of the preamps I need to do a bit mental arithmetic. My measurements show a 6dB increase for PreAmp 1 and a 10dB for PreAmp 2. But please note, even though the data in Table 1 looks spot on, the measured values are rounded up or down to the nearest integer. However, we are talking about an Amateur device not a professional Field Strength Meter. So I'm quite happy with the result.

Here are some older 40m graphs.

Graph 2

Graph 3

Graph 4

Below is my cheatsheet for S-Unit vs dBm vs µV.

Graph 4

CLICK on a graph for a better view.

NOTE: Even though the above graph is displayed with 3dB steps, it is 6dB per S-Unit!

Adjusting the S-Meter in HDSDR

Since ICOM has released Firmware v.1.42 for the IC-7610 the I&Q port is working again. This opened up the possibility to use HDSDR (Sampling rate of 1.92MHz with an effective Bandwidth of 1.66MHz) again. Since I still had the S-Meter check setup "set up" from the "Adjusting the S-Meter in Thetis"  I decided to check and adjust, if need be, the HDSDR/IC-7610 combo.

The setup is basically the same as for Thetis, except the SDR in this case is an IC-7610.

Setup:

• Signal generator: XG3
• Level: -34.8dBm @ 13.8V
• Att: HP-355C & HP-355D (38dB for approx. -73dBm level)

In HDSDR under Options [F7] we find Calibration Setting. This opens the HDSDR Calibration Panel.

Selecting the S-Meter Calibration tab:

The current configuration seems to correspond to an S-Meter reading of S9 +10dB on HDSDR:

and an S9 on the ICOM without the Pre-Amp engaged.

So next we add -73dBm to the Correct Level [dBm] field and press the [Calculate] button.

And the result is:

reducing attenuation by 6dB we get:

and, as expected, adding 6dB we see:

So in a Software Defined Radio (SDR) application written by Amateur's we do get the proverbial 6dB per S-Unit. 

Adjusting the S-Meter in Thetis

After about five (5) years I resurrected my ANAN 100D again. Trying a few versions, including a development version, I settled on Thetis v2.10.3.5 x64 u2. Seems to be running fine on my Windows 11 system. Quite a few improvements over the last five years. Going through the Setup/Configuration of the system I stumbled over a Level Cal inside the [Calibration] tab which can be found under the [General] tab. This allows one the ability to "automagically" set the S-Meter to a user provided level, .... sweet ....

I've decided to use my trusty old Elecraft XG3 RF Signal Source which I have checked against a calibrated RF Powermeter. At 20m the output at the -33dBm level measured -34.8dBm @ 13.8V. So using an attenuator with 38dB attenuation  will give me a -72.8dBm level into the ANAN. A short RG58 cable into a MFJ-1700B switch and another 50cm of RG58 should compensate for the missing 0.2dB to make it -73dBm.

Setup:

• Signal generator: XG3
• Level: -34.8dBm @ 13.8V
• Att: HP-355C & HP-355D (38dB)

And this is how it look in real live.

Here is the Thetis setup:

After pressing the Level Cal [Start] button, the system goes and runs an internal calibration routine. A window pops up to inform us about the progress status of the calibration.

Well, the result is quite pleasing. 

And if we add 6dB attenuation we get:

And not to forget if we do subtract 6dB attenuation the result is:

Struth, 6dB steps who would have thought that is a possibility. 

Oh and this is at every SSB Bandwidth we choose. My default is 2K1, however if I choose 2K9 the S-Meter still shows -73dBm. Yikes, it is possible! It is software defined after all.

It would be nice if my IC-7610 would not change the S-Meter reading with the engagement of the Pre-Amp(s).

References:

• A Little History about S-Points
• IARU Standards
• The beginning of the S-Meter revolution
• IARU Technical Recommendation R.1

IM improvements using DPD with a SSPA

The question that a lot of users seem to have on their mind is "What benefits, if any do I get by using ICOMS DPD in conjunction with a Solid State Power Amplifier (SSPA)"

Well, I measured a 6dB improvement. 

Measurement setup:

• SPECAN: SDR-IQ
• TAP: VK5HW (50dB)
• ATT: 20dB
• PWR: 1000W
• ANT: Dummy Load (VSWR 1.08:1)
• Software: SpectraVue V.3.44 Beta 0

DPD off

Two tone test:

Result:

1st Value    -31.311dB

2nd Value    -31.455dB

3rd Value    -52.398dB

4th Value    -53.545dB

IM Max     -22.2dB

IM Avg     -21.6dB

NOTE: 1st and 2nd are the two tones and 3rd and 4th are IM3.

Look at IM3 and IM5, they are nearly the same in strength.

And the below using my Voice Caller calling CQ:

Result:

1st Value    -23.996dB

2nd Value    -31.168dB

3rd Value    -49.526dB

4th Value    -53.689dB

IM Max    -29.7dB

IM Avg    -24.0dB

DPD ON

Two tone test:

Result:

1st Value    -31.168dB

2nd Value    -31.311dB

3rd Value    -58.996dB

4th Value    -59.139dB

IM Max    -28.0dB

IM Avg    -27.8dB

Well, we do see about a 6dB improvement on the two tone test which is better than a Mosquito fart. But I believe the below is quite a good example on how well it improves your VOICE signal!

And below, using my Voice Caller calling CQ:

Result:

1st Value    -20.840dB

2nd Value    -27.582dB

3rd Value    -57.750dB

4th Value    -60.143dB

IM Max    -39.3dB

IM Avg    -34.7dB

On average we see an improvement of 7dB again better then a Mossi fart.

So I'd say any improvement, be it only 6dB is an improvement. As such I would recommend to upgrade the IC-7610 firmware and enable DPD however, YMMV ....

ICOM IC-7610 Firmware Ver. 1.42 DPD IM measurements

A quick update on my IM measurements for the ICOM IC-7610 with the new Version (V1.42). This Version is the third installment for the '7610 and this one has the I&Q output fixed. I've not tested this but I believe that quite a few forum members have done so and are over the moon.

Here are a few IM measurements I made after the Firmware upgrade.

TRX: ICOM IC-7610

SPECAN: SDR-IQ

SOFTWARE: SpectraVue 3.44 Beta 0

TRX Power: 35W

The above shows the output without DPD. About 23dB 

NOTE: This is 6db below PEP. 

Here we see the same two tone signal with DPD enabled, a nice 54dB down on IM3 and all other IM products are below -140dB. Again, this is 6dB below PEP. So pretty darn good if you'll ask me.

And so the question remains, is it worth to enabled DPD even if we would use an amplifier? I'd say definitely. Using an Amplifier with a much cleaner exciter would give you a cleaner signal (yes yes it depends on a few other things but hope prevails ....)!

Remember GIGO (Garbage in = Garbage out)! This is also true for RF amplifiers not only for Computer Systems.

Nice going ICOM.

See the below pictures how my signal looks over the air. Solid state Amp and DPD enabled. 

• 20m
• 40m

Profiling my antenna using WSPRNet

First things first, if you have a beam or more than one, on a mast or tower that nearly reaches the sky you might want to move on as this is more a process for us mere mortals that live in suburbia and have to live with a piece of wire.

 

I've been trying to get a "feel" for "how my current antenna is performing at my current QTH"! The antenna in question is a 40m Delta Loop, which is slopping from the roofline into the backyard. Now I can model the antenna with one of the many Antenna Modeling programs and using the results I can evaluate if the antenna will perform to my satisfaction. However, it is a model and it will show the antenna to work in an environment that is not indicative to the real environment.

So the next best thing I've done in the past use data from my logbook to get an understanding of the performance of my antenna. However, all this can be speed up these days in using WSPR. I'm not here to explain how WSPR works, except I will reuse the description given by the good folk at WSPRNet.

The Weak Signal Propagation Reporter Network is a group of amateur radio operators using K1JT's MEPT_JT digital mode to probe radio frequency propagation conditions using very low power (QRP/QRPp) transmissions. 

So basically I've setup a WSPR receiver over a period and reported the data to WSPRNet. I could also store the data in my own database, but why reinvent the wheel. Having all the received station data available we could now download all of the data and run it through a graphing/data analysing tool like grafana, gnuplot or Octave.

But why if we have a first class tool written by VK7JJ online directly getting the data from WSPRNet so I don't have to bother with anything else but look at WSPR ROCKS!

As I mentioned I setup a WSPR receiver to monitor the Amateur Radio WSPR frequencies from LF (136kHz) to end of HF (28MHz) and send the collected results to the WSPRNet. I then use the WSPR rocks website to filter out the Band of interest, use the biggest amount of data sets (limited at 5000), select unique calls and select an appropriate time frame.

Lets use the above selected dataset. Initially, the data will be displayed as text first. And to graph the dataset I select <charts> and then <SNR compass>. The result can be seen at the below graph. It is the result from all unique calls which my WSPR receiver heard over a  three (3) day period on the 20m WSPR frequency.

 

I can already see that my antenna is favoring only two directions, more than any other direction.

The question is, can I be sure?

It sure is a good start to visualise the real receive pattern but there is another dataset we can check and then compare it to my recorded dataset. That dataset is the <everyone> dataset. We can select that dataset for a comparison check by setting the <RX call> value (currently set to vk5hw) to everyone. And voila we get ...

This tells me that from 0° to 360°, i.e. around the globe stations where reported for the same time period. Comparing this graph with the graph from my dataset confirms my initial observation. It shows that I have two good and one sort of ok direction were the antenna is performing. The directions between 60° - 110° and 270° - 300° are pretty good. 315° - 25°, well I do receive signals but it seems to be a struggle. There are additional single signals around the 240° and 135° mark but they would be the exceptions due to ... maybe enhanced propagation wich I could find out with a propagation tool (Voacap or GWPS). Now there could have been por or no propagation between me and all those other stations. But even so, I'm confident that this is a good profile of my 20m receive capability at my QTH with the current (40m Delta Loop) antenna. 

There might be the ocasion opening that might give me a better path into those regions which I've received no signal from but those are more likely the exceptions and not the rule. 

Since antennas are a reciprocal passive device, meaning they work the same on receive (RX) and transmit (TX) I'll know which areas of the globe I'll be making easy contact to and were I would have a difficult time to work stations. 

So this is the profile for 20m on the 40m delta loop, and since I use the antenna for 40m, 20m, 15m and 10m as a TRX antenna I need to run profiles for at least 40m, 15m and 10m. Of course I'm also interested in the bands that I only use the antenna as a RX antenna so a few more graphs to compare. However, all I wanted to show is how easy and quick it is these days to profile, i.e. get a good feel, for ones antenna installation at ones QTH. 

Well, most of this is not new to me, but it confirms that I could have done this in three (3) days rather then in 24 month. That's how long it took me to to get to the same conclusion by operating FT8 and SSB from this QTH.

 

A quick Standing Wave check on my antenna system (baselining)

A quick check of my antenna systems SWR (VSWR) tells me that I should be able to use the antenna system on five AR-Band without to much trouble. However a few quick note before heading of to the actual task.

I'm not going to talk about impedances, reactance or admittance. I'm simply checking the SWR to get a basic overview of the overall antenna-systems ability to be used with with my transceiver and/or being able to use a small ATU (Antenna Tuning Unit) to pretend the SWR is "good". It shouldn't really be known as an ATU as it really isn't tuning the Antenna. It is a device using lumped circuits (L's & C's) to present a match to the transceiver output stage. Which is not a constant 50Ω at any of the AR-Bands either. So this quick check of the SWR is enough information which tells me all I want to know (at this stage). 

An additional note. You might have noticed that I always say check and checking the SWR! Well I've never seen a SWR meter that measures SWR (how would we be able to measure a ratio). SWR is not a measurement it is a calculation! Generalised, a VSWR (Voltage Standing Wave Ratio) check is a Voltage measurement of the forward and reflected voltages at one frequency. From those two values the SWR is being calculated. 

So onto the antenna, it is a 40m horizontal loop, attached to two TV roof standoffs to clear the edge of the roof and than slopping into the backyard to a height of 2.3m 5m above the ground.

It is feed with about 3m commercial 450Ω  ladderline to a 1:1 current balun. The rest of the feedline is about 20m of LMR400 and a short run of RG213 and RG8X for the interconnections between the ATU, AMP and the Transceiver. The feedline is heavily chokes with homebuilt chokes.

Measuring from the 213 I'd say I've got 23m of 50Ω feedline to the balun and about 3-4m of 450Ω feeder. My guess is (but I should really measure it) that I don't have to worry about too much loss through the feedline on the four HF-Bands and even on 6m the line should not be to lossy (not sure about the BALUN though, more checking/measuring required).

So how does the SWR look like. (NOTE: If I talk about the SWR from now on, I'm talking about the antenna-system SWR and not the antenna SWR.)

I do not use an inline SWR meter for this purpose, the inline SWR meter is, and that is my believe, only good for monitoring if a change in the antenna system has occured. 

For this tasks and long term comparisons (baselining) I'm using a RigExpert antenna analyser. 

Basically I'll check from after the ATU, i.e. from the end/beginning of the RG-213 upto the antenna.

Below is a picture of the result.

It only displays the five bands that have a reasonable SWR. So let's zoom in a bit.

1. 40m

Bit low in the band, my aim was 7.100 but I thought this wasn't to bad straight of. It shows the VSWR at 40m is good to very good, with an average SWR below 1.5:1.  

The other bands have their best  VSWR outside our allowed frequency allocations. And experience tells me that I'll be able to use my ATU to present an acceptable SWR to the transceiver for proper operation of the output-stage. But even on 40m I should use an ATU to keep the transceiver/amplifier happy as the above 40m SWR plot clearly shows.

2. 20m

On 20m the situation is not as bad as it looks, best SWR is around 13.9MHz. But we also can see that the SWR is not to bad across 14-14.35MHz. With max SWR of less than 4:1 at 14.35MHz. Yes, looking at the Z, e.g. the impedance, I would be able to see if my ATU would be able to tune that. But for now this is all I need.

3. 15m

On 15m the situation is very much the same.

4. 10m

On 10m however, the SWR bandwidth is quite broad and in most cases I'd not need to use an ATU unless I go into the FM spectrum.

5. 6m

And last but not least the bonus Band, 6m. The spectrum I'm mostly interested in, 50.1-50.4MHz has a VSWR greater than 2:1 and would need an ATU to keep the transceiver happy.

Now all this means is that I should be able to operate on these bands without to much trouble. The ATU's build into the newer type of Radios and Amplifiers with their 3:1 tuning range should find a suitable match without breaking sweat. And, my trusty old YAESU FC-901 ATU is able to tune the four HF bands easily without getting warm at 400W.

So now that I have this data "stored" I can say that I have baselined my antenna system. I can now refer back to this data to see if, over time changes have occurred.  

Last thoughts:

• For an antenna SWR the SWR should be checked at the antenna itself rather than at the end of the feedline. The feedline will load the antenna and create an illusion of having a better antenna SWR.
• To fully understand your antenna-system, feedlines (transmission lines) should have their attenuation (cable loss) measured or calculated (length measurement tape-measure  or TDR).
• Knowing the above, one can calculate the SWR at the antenna feedpoint.
• I would not use an inline SWR Meter for any of the above measurements however, using an inline SWR-meter is good insurance policy because connection problems usually show up as SWR spikes which can quickly be seen on those type of meters during operations.