Why does my S-Meter read S5 all the time?

Mark K1LSB

Lee, the Flex S-meter doesn't work like an S-meter should.  The published spec says, for example, that if the maximum noise strength as measured anywhere in the passband is at .79uV (microvolt), then the S-meter should read S3.  But the Flex S-meter will measure something more than that, dependent on how wide the passband is.  So if you're listening to a wide slice of S3-level noise, the S-meter on your Flex might read S5 instead of S3.  So if there's a signal in there that's actually at an S4 level, you'll be able to hear it over the S3 noise floor, even though the Flex S-meter is reporting that the noise floor is at S5!  Why Flex decided to do things like that has never been satisfactorily explained to me.  But that crazy way the Flex S-meter operates gives rise to some equally crazy claims that "the Flex can hear signals below the noise floor", which is absurd.

Carry on,

Mark

Lee

What are you guys talking about...Antenna shorted and it hears RF...from what...The short wire inside the unit? Yes of course there will be a VERY small amount...but S5!
If it hears anything with the antenna shorted..it must from inside the radio.....I don't think it is any more sensitive than any other modern radio. A good friend of mine did A/B testing with another high end radio with many weak DX signals and the Flex using very good antenna's and the Flex while very good....was not quite as sensitive when copying weak DX, even though the selectivity was better. The only way with the antenna shorted at the radio to get the hiss to lower at all is bring down the AGCT to a very low level....Is my 6400 needing repair?

By the way the reason I got into this question of S/N ratio was lately I have been experimenting with BOG antennas to improve S/N ratio on 80 mtrs. When we switched to the BOG and the noise and S meter stayed high we said..What the heck is going on here.....

Lee

Mark, it's not just the S meter....Why is the white noise the same with NO Antenna?

Lee

What? Hear below the noise floor...how...Maybe below the S meter reading...but the actual atmospheric noise floor?

Bill -VA3WTB

This is pasted from Steve explaining some of this..

The panadapter simply measures the signal in a given bandwidth and draws what it hears. If you look at any given pixel, it represents a certain amount of bandwidth. We call this the "bin size" of the FFT that is used to produce the display. If you cut the bin size into two pieces, the amount of noise in each piece goes down by half (3dB). In PowerSDR, the bin size is generally fixed for any given setup and does not change when you zoom. This is why the resolution gets worse as you zoom in on PowerSDR -- you begin to show one bin with multiple pixels. But for SmartSDR, we knew we wanted to have a larger range of zoom and this method was no longer acceptable. So we vary the bin size across a 1000:1 range. So the noise in each bin also varies. 1000:1 is a change of 30dB so from min zoom to max zoom, the noise in a bin will lower by 30dB and you see this change in the panadapter as you zoom in and out. 

When people talk about noise floor in ham radio they are generally talking about the noise level with a 500Hz bandwidth. When the panadapter is zoomed in to the max level, the bin size today is about 5.8Hz. This is a 19dB difference in noise from where a ham would say the noise floor is to what you can see on the panadapter. This means that the panadapter can see 19dB below what most hams would call the noise floor. Your ear and brain are also able to hear below the noise floor in 500Hz because of how they work. But there are limits to how well you can hear. If you've ever worked JT65 or another long-term integrating mode, you have noticed that your computer can copy signals that you cannot hear. 

Mark K1LSB

Bill, that's the same post of Steve's that you copied and pasted a month ago in this same thread.  As I said then, I don't care about FFT bin size, and neither should the S-meter care about FFT bin size (at least not unless you zoom in to a microscopically small slice of spectrum).  I've stated before that the S-meter reading should have no correlation to passband width or zoom or anything else except the maximum signal (or noise) level detected anywhere in the passband.  If the maximum voltage detected anywhere in the passband is 3.2 uV then the S-meter should read an S5, regardless of whether the passband is 500 Hz wide or 500 kHz wide.  In reply to your cut-and-paste a month ago in this thread I posted links to two videos I made from inside an SDR Console session where I varied the passband width everywhere between 20 Hz and 350 kHz, and the zoom between 200 Hz and 1.4 MHz, with virtually no change to the S-meter reading.  Here are those videos again:

https://drive.google.com/open?id=1jSQUm_SXCRfpWiPGnADd-Ple3mk5x6My

https://drive.google.com/open?id=1KJwBKiJXdHBCaw0MpGjGg6dNYp4Upgjv

You either didn't listen to a word I said back then, or you're not capable of understanding, because you just keep copy-and-pasting the same stuff over and over.

Simon Brown got it right in his SDR Console software.  Wolfgang Link also has a clear understanding on his page here:

http://www.giangrandi.ch/electronics/radio/smeter.shtml

For the record, he is the author of Methods of measurement for amateur radio (ISBN-13:978-8870210781)

KY6LA_Howard

Wolfgang Also Says This refers to an unmodulated carrier signal (N0N) that uses almost no bandwidth; in case of real signals using a given bandwidth, this definition may not be enough since a smaller receiver bandwidth allows a weaker minimum detectable signal, but S-points are still a good tool for comparing received signals.& So Wolfgang agrees with flex when you measure @500Hz bandwidth

Bob W8RMV

What I don't understand is how the Flex method is better than the old method.  What is gained by the Flex method?  It seems that the Flex signal strength gage is useless below S5.  If it is useless, then why even have it?  If it is useful, nobody has stated its value when showing a constant ~S5 no matter if you have the SO239 shorted or not.  Every other radio I have shows an S0 when I short the SO239.  In fact when I would align older radios, I had to first mechanical zero the meter, then electrically zero it & then set it to spec for a S9.  This method has worked relatively well for decades.

So I am still missing the point/value of having a Signal Strength Meter read almost S5 when the SO239 is shorted out.  And apparently, I am not the only one.  The S meter only makes sense, when it shows the signal strength above the zero signal point represented by a shorted SO239/N connector.

Bob W8RMV

Jay Nation

I can't ever remember giving the "Panadapter Noise Floor" a signal report. Never heard it call CQ either.

#Flexradio

73, Jay / NO5J

Jay Nation

I can't ever remember giving the "Panadapter Noise Floor" a signal report. Never heard it call CQ either.

#Flexradio

73, Jay / NO5J

Mark K1LSB

Show me where Wolfgang specifically agrees with Flex's S-meter reading at 500 Hz bandwidth.  He doesn't.

Nor does he at all agree with Flex's position that S-meter reading varies linearly with bandwidth.

Bob W8RMV

Said in maybe a more impactful/descriptive way, just display a Flex S meter that starts a S5/ -97dBm, since the S meter indication below that level does not impart any useful information.

Bob W8RMV

Stan VA7NF

Really tired of the repeated comments, and this may be one too.
The 'S' meter will measure a real CW signal the same at any bandwidth.  
As with 'other' radios if there were 4 CW signals within the bandwidth it would read the sum of the signals.
With noise (antenna or other sources) it still sums the signals which on larger bins may be 1000 times small bins.  Hence a strong signal will remain the same and summed noise will steadily increase with the capture area.
Give it a rest unless all you want to do is fill this forum with wide band NOISE!

Bill -VA3WTB

I am pasting in Steve and Tims responses to these questions so people asking will understand how the flex works in this regard. I know there are people here who think Steve does not know what he is doing, I am not one of them. From my reading and seeing how Lab signal generators work I believe the Flex engineers have it right.

Lee

Guys, no one listened to me...I'm NOT talking about measuring real signals here....I am talking about the noise floor...I'm beginning to think Flex has a high noise floor. I had a TT Orion II a few years back...very low noise floor displayed on P adapter, S meter AND the actual band noise with no signal. 

No one here has explained why with a shorted antenna I have S5 and lots of HIS...S5 is -104 DB...that's a lot of RF, where is it coming from with the antenna shorted?? When I tried a low noise BOG antenna the band noise did not go down, Why...maybe the noise IS coming from the radio even with a shorted or 50ohm terminated (I tried both, no difference) antenna port. LAst night on 40, we had a very weak signal on Freq. the ONLY time I could hear him was when his signal was OVER S5 (the band noise on my 6400. When I could not hear him, the panadapter did NOT show any signal. When I watched carefully...I just began to hear him when I could just see his signal rise above the panadapter line.

Let's talk real here not engineering talk that may or may not be practical in operations.

Bill -VA3WTB

What I posted explains all that you asked,,read it. Steve and Tim explains why.

Mark K1LSB

"As with 'other' radios if there were 4 CW signals within the bandwidth it would read the sum of the signals." -- Stan VA7NF

Wrong, Stan.  Let me say this one more time, since you apparently weren't listening the previous dozen times I said it: The only thing an S-meter should be reporting is the highest instantaneous voltage measured at any single point anywhere in the pass band.  There is no 'summing" that should be taking place.

Here's a video I made this morning of some digital activity on 40 meters, running Simon Brown's SDR Console V3.  Note the S-meter only registers the greatest single signal level found inside the pass band, regardless of how many signals are present in the pass band, and regardless of how wide the pass band is.  There is no "summing of signals".

https://drive.google.com/open?id=1ememj-2hZX6fIFEVvBr6tyk4evN8zldu

That's how an S-meter should work, and that's the only way it should work.  If there were any summing taking place, then the S-meter reading at the instant the video stops should have been well over S9+50!

Any notion of "summing of signals" is pure nonsense.


@Bill VA3WTB,

You've done nothing but repeatedly point to other people's posts while contributing no thoughts of your own.  So thanks for the "wide band NOISE" (to use Stan's term).

Bill -VA3WTB

Stan, to be clear, I use information from the experts, both Tim and Steve are. I am not an expert and have not been involved with the engineering of Flex radio.

So yes, I plan to continue using their expert information to inform others.

Bjørn Lindberg

Hi. Any progress with changing S-meter to get same readout like all other producers of radio ? A bit tired looking at the meter reading s4,5 then nothing connected to radio. My radio is Flex 6600m. Please fix this Flexradio ! Regards Bjørn / la5vsa

Tim - W4TME

@Bjørn Lindberg This is not something we are planning on changing as it is not broken. The S-meter is accurately measuring the RF power in the defined receiver passband just like all spectrum analyzers do. This was a core design decision to allow our radio be be used as lab grade spectrum analyzers in addition to being a high performance multimode receiver.