What are Signal Reports? What is an s-unit? Why does this matter?

[marcspaz]

What are Signal Reports? What is an s-unit? Why does this matter?

But, Why?

First, why does any of this matter?  The General Mobile Radio Service was segmented with the concept of being a short-distance two-way communications for licensees and their immediate family members.  It doesn’t require any special knowledge, exams or understanding of the science behind the magic. However, you will occasionally hear both professional and amateur radio operators who are also licensed GMRS operators, who may be using lingo more common to other services.  One of the most common will be an RST style signal report.

I’ve noticed that many new operators will call for a radio check, especially on a repeater.  They may get a 'signal report' from a Ham that sounds like this, “I copy you five nine.” Or you may hear “You are full-quiet into the repeater.”  While these answers may be true and accurate, for new operators, hearing “Your radio sounds great” or “I can hear you fine, but there is a bunch of static. How far are you from me (or the repeater)” would likely be a lot more helpful.

Well, in the event that you come across me or one of my well-seasoned friends and we forget that not everyone knows what we are talking about, this may help you understand what you are hearing with regard to signal reports… and if you would like to use the same method, provide you with the best guidance I can.

What are RST and Signal Reports?

The RST signal reporting system is primarily used by amateur radio operators and other radio hobbyists to exchange information about the quality of a radio signal being received.  The original reporting system was created to be used with Morse Code, and is a three digit number.  Each digit is used for conveying an assessment of a signal's Readability, Strength and Tone (RST).

Over time, amateurs adopted this reporting scheme for voice communications as well, but it was modified a bit to be more friendly to reports about voice signals.  Readability is still used to define how intelligible your voice is; meaning how well can I understand what you are saying.  Strength of your signal is also still used, based on the meter on the receiver’s radio.  However, Tone was dropped for voice reports.  Though on occasion you will hear someone tell an operator, in plain language, if their transmitted signal has too high or too low of a tone, as some radios allow the owner to adjust the tone.

Readability –

This part of the report is subjective, but still helpful.  Readability is used to define how intelligible your words are, on a scale of 1 to 5.  A readability value of 1 means that I can tell you are transmitting and talking, but I can’t make out anything you are saying.  A readability value of 5 means that, regardless of anything else, I can understand every word you say. A report with 2, 3 or 4 would be some variation between 1 and 5. 

Some examples on how I personally would rate your readability on GMRS would include a 2, meaning I may be able to hear enough of what you’re saying that in a life or death situation, it may be enough to get help going.  With a 3, I may be able to understand 3 or 4 words out of every 5 words.  We can talk, but it’s kind of a hassle.  A 4 would be I can hear every word but there is static.  Pretty straight forward.

Strength –

With regard to strength in a signal report, there is nothing subjective about it, sort of.  Unfortunately, if it is scientific or subjective depends on your radio meter type and if the meter is calibrated.  We are actually measuring the voltage of your signal on the receiver’s radio.  This voltage is measured in S-units or Signal Units.

Where this can get tricky with GMRS is, not every radio has a signal strength meter designed to support the common s-unit scale.  You may have a display that shows 9 units on some unknown scale, or 10, or 15.  I have even seen some radios that only have 4 or 5.

I’ll explain the technical parts of signal strength measurements and if you have a radio that doesn’t use a traditional calibrated s-meter, you may be able to adopt the idea to your personal radio.

This meter below is a classic analog meter.  The top line measures the received signal strength in s-units.  If the needle were to swing to 5, you would give them a 5 as the Strength portion of the report.  For example, if you understand every word and the needle stops at 5, you would provide a signal report for their voice signal of “five five” or “5 5”.  If you could hear all of the words they are saying with a lot of static and the needle is on the 3, you would report a “four three” or “4 3”. 

 

Below is a newer radio with a digital s-meter.  It looks a little different, but the same rules apply.  In this picture, my meter is showing a signal strength of about 5.5 (almost 6) s-units.  If I could hear them perfectly, I would tell them their signal report is “five five plus” or “5 5 Plus”, meaning I understand everything perfectly and their signal strength is never less than 5.

 

Now, the next two images show a radio that I know doesn’t have a properly labeled or calibrated s-meter. This type of meter is the reason I said there is nothing subjective about it, sort of.  While an s-unit is a true measurement of voltage, this radio has 10 lines and nothing in the owner’s manual tells me what the increment values are.  However, you could still adapt the concept to a signal report, making it a bit subjective.

In the first image, the meter is completely full.  In this state, it’s very likely that I can hear the person talking perfectly and they almost certainly met or exceeded the voltage requirement of 9 s-units.  So, I would tell this person that they are “five nine” (5 9) or they are “full quiet”.

 

In the next image, below, the signal goes to the fifth line.  Being familiar with this radio, there is a good possibility that I can hear everything they are saying, but with a lot of static.  So, I would be providing a signal report of “four five” or “4 5”, since the meter measurement is half the total scale.  In this case, the signal report is 100% based on my interpretation of what I am hearing and seeing, rather than providing a “metered result.”  I hope this makes sense.

 

For those of you who are interested in the science behind an s-unit, here is a little history and values.

In the 1930s, the industry agreed that 9 s-units would correspond to 50 microvolts (50 μV) at the input of a receiver.  However, based on meter design and how the value was sampled, this was not accurately measured from radio to radio because the input impedance of receivers was not standardized.  This changed in 1981.

The International Amateur Radio Union (IARU) agreed on a technical recommendation for S Meter calibration, separately for HF and VHF/UHF.  IARU defines 9 s-units for the HF bands to be a receiver input voltage of 50.2 microvolts and impedance of the receiver of 50 ohms.  For VHF and UHF bands, the IARU defines 9 s-units to be a receiver input voltage of 5.01 microvolts and impedance of the receiver of 50 ohms.

For both HF and below, as well as everything over HF, the IARU defines that a difference of one S-unit corresponds to a difference of 6 decibels (dB), equivalent to a voltage ratio of two, or power ratio of four.  For example, if 9 s-units equals 50.2 μV, than 8 s-units is 25.1 μV, 7 s-units is 12.6 μV, etc.

Signals stronger than 9 s-units are given with an additional dB rating.  For example, “20 dB over S9” or simply "20 over".  You can see these values on the s-meters in the first 2 images.

Repeater Caveat

There are some important caveats to signal reports for repeater users.  The RST style signal report is not a valid reporting method.

The voice quality or 'intelligibility' of the transmission is likely not going to be valid.  If the reporting operator is receiving the repeater's signal well enough that there is little to no chance that the voice quality is impaired, you may be able to give and get a valid readability report.  This condition is often when you will hear signal reports such as "loud and clear" or "full-quiet."  These replies indicate that you have a very good radio and voice signal into the repeater, as reported by someone who has a very good signal from the repeater.

Additionally, the signal strength is not relevant through the repeater, at all.  The receiver's station is going to be seeing the signal strength of the repeater, not the originating station asking for a signal report.  It is not possible to know the received signal strength at the repeater site unless you are the repeater owner or admin and have the ability to see the actual repeater's receive meter.  Even then, most repeaters do not have any easily visible signal strength meters. 

The next best method would be if the receiving station listens to the repeater input frequency (assuming the receiving radio has that feature).  If the reporting station can hear you directly, they can tell you how strong your signal is at that person's location.  It's still not indicative of how strong your signal is at the repeater.

I hope this information helps anyone who may hear this lingo out on the General Mobile Radio Service.

Quick Reference Chart for S-Units

 

Edited February 23, 2023 by marcspaz
Updated Thread and Section titles for clairification for "Some People" to parse the information easier.

[Lscott]

marcspaz

You did a great write up on this. It should be required reading.

[marcspaz]

10 minutes ago, Lscott said:

marcspaz

You did a great write up on this. It should be required reading.

Thank you so much for the kind words.  It is much appreciated.  I really do hope it helps.

[Lscott]

1 minute ago, marcspaz said:

Thank you so much for the kind words.  It is much appreciated.  I really do hope it helps.

Writing up technical material isn't easy to do, time consuming and trying to make it understandable takes a good bit of effort.

I've done it at my work place a few times. I can appreciate what goes into it.

[SteveShannon]

This is absolutely excellent information, Marc.  Thank you.  @Lscotthit the nail on the head.  Documenting technical information clearly is a gift.  You did a great job. I really appreciated the historical aspect as well.

[marcspaz]

 

A friend of mine reminded me about something pretty important.  I updated the original post, but wanted to include the update here as well.  With new or non-technical operators, this is an often misunderstood concept.

 

Repeater Caveat

There are some important caveats to signal reports for repeater users.  The RST style signal report is not a valid reporting method.

The voice quality or 'intelligibility' of the transmission is likely not going to be valid.  If the reporting operator is receiving the repeater's signal well enough that there is little to no chance that the voice quality is impaired, you may be able to give and get a valid readability report.  This condition is often when you will hear signal reports such as "loud and clear" or "full-quiet."  These replies indicate that you have a very good radio and voice signal into the repeater, as reported by someone who has a very good signal from the repeater.

Additionally, the signal strength is not relevant through the repeater, at all.  The receiver's station is going to be seeing the signal strength of the repeater, not the originating station asking for a signal report.  It is not possible to know the received signal strength at the repeater site unless you are the repeater owner or admin and have the ability to see the actual repeater's receive meter.  Even then, most repeaters do not have any easily visible signal strength meters. 

The next best method would be if the receiving station listens to the repeater input frequency (assuming the receiving radio has that feature).  If the reporting station can hear you directly, they can tell you how strong your signal is at that person's location.  It's still not indicative of how strong your signal is at the repeater.

[axorlov]

To defend my statement from the other thread, that RST scale is all about psycho-acoustics, here is the link to QST from November of 1934, with article from the inventor of RST scale, page 18: http://www.rsp-italy.it/Electronics/Magazines/QST/_contents/QST 1934_10.pdf  Notice, there are no microvolts, and his proposed S scale had only 5 steps. Only decades later the current scale was adopted (50 uV over 50 Ohm over 9 steps).

RST was developed for report on CW, and later adopted to voice modes AM and SSB by dropping the "T". It's all good, because on AM and it's derivatives (CW and SSB), the "R" is not directly related to the strength of the signal, and the "S", the strength of the aural, is directly proportional to the strength of the signal. The bigger, fatter the signal, the louder the voice you hear.

Funny thing, the RST/RS scale is not applicable to FM. Or better to say, RS is applicable, but S-meter will not tell you the strength of aural. When working with FM, the "S" part, the strength of the aural has nothing to do with the strength of the signal. With signal strength above certain threshold, S is always 9. And if your correspondent sounds too quiet, it means he is on Baofeng with it's trademark 5K0F3E emission, or maybe he should blabber louder. However, the "R" part has everything to do with the strength of the signal.

 

[Blaise]

On 2/20/2023 at 11:38 AM, marcspaz said:

I hope this information helps anyone who may hear this lingo out on the General Mobile Radio Service.

You rock, man.  Even when I think I know, I still always learn more when I read your write-ups.  You should very seriously write a book!

[marcspaz]

@axorlov, I'm not sure why you keep coming back to this. Nothing you have shared is relevant to how things are done for voice, today. Outside of a history lesson (which is actually really entertaining to read and learn about), what was created for CW 90 years ago has nothing to do with what is used for voice today. And aural has nothing to do with the signal strength in today's method.

 

You can either choose to use the current globally accepted method used for voice or not. That doesn't change how and when it's used today.

[axorlov]

I think I explained well, but I summarize one more time. On FM, signal strength (what S-meter shows) has nothing to do to with "S" on RS scale. On FM, signal strength (what S-meter shows) has everything to do with "R" on RS scale. Bringing S-meter into conversation when talking about RS scale on FM is a silly fetishism. You ether talk about RS report or talk about what S-meter shows. These two things are not mixable on FM, like kerosene and hazelnuts.

2 hours ago, marcspaz said:

has nothing to do with what is used for voice today

You are incorrect on this. RST scale is absolutely used as designed 90 years ago for the same purpose it was designed 90 years ago, in the same exactly way as it was designed 90 years ago, on AM, SSB and CW. Innumerable articles, starting with ARRL Handbook will tell you that.

[marcspaz]

 

Alex... Man,  I am trying so hard to be nice/respectful, but I am totally bewildered by every response from you and I am starting to get a little upset.  Like, it's giving me a headache.  I will do what I can to make this as clear as possible.  Read the next two sentences very carefully, and then read it again.

I am NOT discussing RST reports for CW.  I am talking about a modern Signal Report for analog voice, with origins rooted in RST. 

This is going to be my last reply to you on this... the only two reasons I am replying at all is because I am hoping what I'm writing will finally make sense to you, and to explain to new operators and non-hams who may hear this lingo, what it is that Hams are saying to them.

 

One more breakdown... please read carefully.

The radio's s-meter is literally, exclusively reflecting the signal strength and in the current/modern Signal Report, the S represents signal strength.  You get the signal strength from the s-meter.  Period.  End of discussion.  We are not using RST for voice.  The Readability (intelligibility) of the words being spoken describes how well the listener understand what you are saying.  That's it.  Nothing else.

  

5 hours ago, axorlov said:

You ether talk about RS report or talk about what S-meter shows. These two things are not mixable on FM, like kerosene and hazelnuts.

I am talking about modern signal reports.  There is no mutually exclusivity.  The s-meter literally provides you with a measured value (if the meter is properly calibrated) for 50% of the report you are delivering.  Unless you are not using a modern analog voice signal report scheme, you can't provide an accurate signal report without a calibrated s-meter.  The requirement for a calibrated meter is why I said it could be scientific or subjective, depending on your radio meter type and if the meter is calibrated. 

  

5 hours ago, axorlov said:

You are incorrect on this. RST scale is absolutely used as designed 90 years ago for the same purpose it was designed 90 years ago, in the same exactly way as it was designed 90 years ago, on AM, SSB and CW. Innumerable articles, starting with ARRL Handbook will tell you that.

I don't participate in CW exchanges, so I can't speak to how the RST reports are being used today.  However, I can say (agreeing with you) the original RST reporting system was created to be used with Morse Code.  However, I am NOT explaining the original RST reporting system.  I am explaining the current signal reporting system, that has been adopted from the original RST system, for the purpose reporting voice quality and signal strength for all analog voice communications that amateur radio operators use and that GMRS operators may be exposed to.  CW RST reports have nothing to do with this, beyond the origin story.

[axorlov]

On 2/21/2023 at 9:01 PM, marcspaz said:

I am talking about modern signal reports

On 2/21/2023 at 9:01 PM, marcspaz said:

We are not using RST for voice

On 2/21/2023 at 9:01 PM, marcspaz said:

However, I am NOT explaining the original RST reporting system.  I am explaining the current signal reporting system, that has been adopted from the original RST system

First it was RST report (look at the topic name!), and now it is "modern signal report"? I explained why using S-meter in context of RS/RST scale with FM voice is meaningless and misleading. I also explained why the original RS/RST is still in use for AM-SSB voice today. Not any "modern signal report", but very original RS scale, extended to 9 levels of "S" in 1936.  But if you feel that it is Period End Of Discussion, so be it.

Edit (2 days later): Marc chose to change the topic name. It used to say "What are the RST reports, and why does it matter". Who knows what else he decided to change postactively, I'm not reading. He is now in the same bucket as a certain dude whosE name ended with ..LAX.

[WQWX838]

Well, Logged in after not having been on here a while, and saw this thread. Thanks to Marc for taking the time! I shudder at the thought though of "ham" style culture becoming the "norm" for GMRS. Please refrain from emotional reactions, but I promise everyone that if this "cultural" situation of "hammy style" becomes the norm? GMRS will be in trouble. Using CW lingo/shorthand for voice modes is one of the operating habits of hams that are not the best. How many times have you heard the propane delivery guy using ham lingo when on the radio? Aircraft? EMS? Timber crews? Pipline? Railroad? Marine SSB (not ham but actual maritime SSB), Coast Guard, I can go on and on!! The phonetic alphabet is essential at times, and important to learn. Utility use is "inclusive" and using ham lingo is "exclusive"...

[marcspaz]

@WQWX838 I agree. I really think that it's in everyone's best interest to speak plainly. Unfortunately I hear a lot of lingo from Ham and firsr responders on the repeaters in the DC metro area. Many Hams use GMRS like its amateur radio, to the point where one of my friends revoked permission from a bunch of people on his repeater. 

[WQWX838]

Yes!!! I totally support your pal in what he did with his repeater. It is as though we need to have some kind of "intervention" for hams once they come to GMRS. I dare say that holding a zoom meeting with camera's and faces where discussion about the inappropriate habits that "hams" develop would be addressed. It is NOT about "good people" or "bad people", yet bringing out into the light, an open discussion of the horrid operating habits that "hams" rapidly develop. It would be like some type of initial "repeater orientation" style meeting which would be a requirement before a repeater owner will allow access. I can't see any other way to deal with this other than head on...

I SAY AGAIN! Utility use is people inclusive! Hammy ham lingo makes it people exclusive!

[axorlov]

• 11 hr marcspaz changed the title to What are Signal Reports? What is an s-unit? Why does this matter?

(2 days later): Marc chose to change the topic name. It used to say "What are the RST reports, and why does it matter". Who knows what else he decided to change postactively, I'm not reading. He is now in the same bucket as a certain dude whose name ended with ..LAX.

[marcspaz]

25 minutes ago, axorlov said:

• 11 hr marcspaz changed the title to What are Signal Reports? What is an s-unit? Why does this matter?

(2 days later): Marc chose to change the topic name. It used to say "What are the RST reports, and why does it matter". Who knows what else he decided to change postactively, I'm not reading. He is now in the same bucket as a certain dude whose name ended with ..LAX.

I changed the title because, as you pointed out, the title was a bit misleading.  You made a valid point to which I conceded, yet you act like an ass.  Stay in your lane son... the same guy who said "one s-unit is when human ear can tell the difference between levels of AM signal" has no business criticizing anyone else's understanding of technology. 

Updated Thread and Section titles for clarification for "Some People" to parse the information easier.

 

 

[axorlov]

30 minutes ago, marcspaz said:

the same guy who said "one s-unit is when human ear can tell the difference between levels of AM signal" has no business criticizing anyone else's understanding of technology

You may need to expand your horizons just a tiny bit. Engineering types and techno-fetishists are known to not be able to see the forest behind all the trees, but your specific case is remarkable. Especially, after bringing mine and yours exchange from the other thread, where I explain to you what stands behind today calibration of S-meter and where the root of all of this. Read it again. Good luck and good bye.

Edit: By the way, changing topic name and changing text/wording for the contested theme is dishonest. I'm not going to waste my time for you anymore.

[marcspaz]

1 hour ago, axorlov said:

You may need to expand your horizons just a tiny bit. Engineering types and techno-fetishists are known to not be able to see the forest behind all the trees, but your specific case is remarkable.

Man, you have no idea who you're talking to. LOL.  I'm independently wealthy.  I have owned my own business for decades. I have a wife, kids, grand kids that I love and spend a bunch of time with.  Along with a decades of studies in my field, I spent 7 years studying Constitutional Law and the founding and framing of the US.  I have dabbled in politics, contributing to State level legislation.  I have been an engineer since 1984 and have more licenses and certifications than I know what to do with, including two new certifications in the last 2 months. As an independent consultant, I have 13 years supporting the Department of Homeland Security; another 10 years supporting DoJ as well as DoD and I am currently an engineer working at the Pentagon.  I love long-range shooting, have participated in professional level auto racing, 4-wheeling and I have been playing radio for 35 years, including being a licensed Amateur for 2 decades.  Oh!  I almost forgot, I started ground school recently and I am working on getting my private pilot license.

I feel like my range of knowledge, understanding and experience are fairly vast.  Though, I guess I can still do more (shrug).

 

1 hour ago, axorlov said:

Especially, after bringing mine and yours exchange from the other thread...

 

Just a quick reminder, you are the one who's very first post in this thread was bringing BS from "the other thread".  I am just playing by your rules.  See below...

 

 

1 hour ago, axorlov said:

...where I explain to you what stands behind today calibration of S-meter and where the root of all of this.

 

Yeah, about that... you're still very, very wrong about s-meter calibration and it's roots.  SMDH.  Saying the wrong thing over and over again doesn't make it right.

 

1 hour ago, axorlov said:

Edit: By the way, changing topic name and changing text/wording for the contested theme is dishonest. I'm not going to waste my time for you anymore.

 

I'm missing how it's dishonest to recognize the confusion of the original title (something you pointed out, I may add) correcting it and then literally making a note of what I corrected and why.

I really do hope you are done posting in this thread, though.  All you are doing is reaffirming your lack of knowledge and derailing a thread that was actually helpful.  It's a train wreck now.  With any luck, Rich will clean this thread up and lock it.