It is said that a picture is worth a thousand words, so I will keep this post brief by posting only two charts. The first is just below:
As pointed out in his most informative article titled Interpretation of S-Meter Noise Floor in HF Receivers by Basu VU2NSB [link below] the ‘noise’ any given amateur radio operator experiences will depend a good deal on the location of his or her station.
To assume that the entire band is ‘noisy today’ based on what we hear or a measurement taken by using our personal transceiver’s S-Meter is just that, an assumption…far too often with no proof for the assumption given or even sought.
Do you agree? Disagree? How do you measure Noise Level?
Please use the ‘Reply’ section below this post or contribute your own Post if you have some thoughts on the matter.
The purpose of the ’80 Meter Study Group’ of the Forum is to stimulate discussion and the sharing of knowledge so I will leave this chart and present one other below.
The chart above, also created by Basu VU2NSB, illustrates another inconvenient truth. The methodology used to create the chart is described in the article referenced above.
The S-Meters in use by amateur radio operators around the world differ significantly from radio to radio.
On the Hudson Valley 80 Meter Net we have had participation from over 117 stations from the Canadian Border to the Long Island Shore located in 28 New York counties and eight states in the last six months.
A ‘5-7’ from one station may not be equivalent to the same report from another.
During a recent HV 80 Net one station remarked that another was an ‘S-2’ while the other station said, ‘…and you are an S-9 here, armchair copy.’.
How reliable are the reports we give based on using our S-Meters and more importantly what information is best to use if Station Optimization is our goal?
Again, if this issue interests you and you can supply relevant information, thoughts or critiques, your comments are most welcome in the Reply section below or through your own post.
Thanks for reading this post and hopefully sharing your thoughts which will help us all to learn with and from one-another.
References:
1.Interpretation of S-Meter Noise Floor in HF Radio Receivers; https://vu2nsb.com/s-meter-noise-floor-hf-receivers/.
2. Radio Transceiver S-Meter – Pitfalls to avoid; https://vu2nsb.com/radio-systems/amateur-radio-station-ham-shack/radio-transceiver-s-meter/.
So, what is an S meter and how does it work? Well, back in the good old days, the volume in the earphones of your crystal set was directly proportional to the signal strength of the station you were listening to. The higher the power and / or the closer you are to the transmitter, the louder the signal. Low power transmitters at a far distance, you hear nothing. That's no fun....
The vacuum tube was invented. Now, we can amplify and hear those weak, distant stations! But, that powerful transmitter in town would overload the vacuum tube amplification stages, putting it into saturation and greatly distorting the audio to the headphones or speaker. There has to be a better way! In the early 30's, manufacturers developed an Automatic Volume Control, or AVC. They would sample the audio level, or the RF level out of the IF amp. This sample was rectified and filtered to generate a DC voltage proportional to the strength of the received signal. This DC voltage was used to reduce the gain of the previous amplification stages. Now, you have full gain for weak distant stations, and reduced gain for strong local stations. Everybody sounds good and at similar volume levels! Cool!!!
As technology evolved, and the AVC got better, the question arose as to how do we know how strong a transmitter's signal actually is? Well, the stronger the signal is, the higher the AVC control voltage is. So, by putting a volt meter on the AVC control voltage, we can measure a transmitter's signal strength. Well, that's cool, but what do the numbers on the meter mean? Collins Radio developed a standard years ago. They coined the term S unit. They decided that there would be a 6 dB step from one S unit to the next. That represents a 4X power increase from one S unit to the next higher one. They Pinned the scale at S9 being 50 microvolts, or -73 dBm into a 50 ohm load. In 1981, the IARU, International Amateur Radio Union adopted the Collins Standard.
So, now we have a STANDARD! YAY!!! Nobody else cared. Thus, the chart above... Nice try..... Interestingly enough, the signal levels don't even track from one model to the next from the same manufacturer!!!
Jim K2BHM