The service agent was great in communication via email on the updated on my repair and also showed concern on the care and treatment of my transceiver. I would give that person a 10. "However, my S meter problem is still NOT fixed." I have spent the time reading all the back posts dealing with S meter readings, and I join the group in frustration that you seem to want to re-create the whole purpose for the readings, rather than fixing the issue. So, in the future do to my Flex, with or without an antenna connected or pre-amp on or off, RF/AGCT turned off or full, the S meter readings remain 5-6 plus at ALL times. I will report back to all my contacts that, SINCE I have a FLEX radio I am UNABLE to give you even a close, approximate, true reading of your signal level.
To revisit the main points: without all the math that follows this topic. I have seen Steve explain all this with all the charts and graffs, with math that tires the mind out, I will skip all that and just make this simple...
1 in a receiver there is no such thing as 0 noise. In the radio receiver noise is always present internaly and there are several types of noise in the receiver.
2 in an SDR receiver there are receiver bins, these bins are being digitally sampled all the time. Each bin has noise in it. As we expand our receive band pass filter we expand the number of bins being sampled, thus the noise increases the same amount. Now if we narrow our receive filter to it's smallest, we then are only sampling a much smaller amount of bins, thus the noise is much less.
As we do this we can see the noise go up and down as we change the filter size with the S meter read out. On my 56500 at the smallest filter size my S meter reading is around S1 or a little lower.
3 The way Flex desined the S meter is to work just like laboratory equipment that reads signal and voltages to signals.
The S meter in your Flex is alway reading the digital samples from the receiver bins, this is what your seeing as the receiver is dead without the antenna. If the meter reads 0 with out the antenna, this would be incorrect because there is always noise. If it read 0, then what happened to the noise in the bins? It's still there. If it's there, then the Flex will detect it.
But when an antenna is connected the S meter will read as low as 0 without a signal at all. That would be impossible due to the band noise floor. But in most cases a low signal we can hear will be around S 3 or higher and the meter will reflect that.
In any case, the S meter on a Flex radio is very very accurate. so when you give someone your reading it will be as close as it can be.
There have even been suggestions that Flex purposely add a software switch to approximate the largely uncalibrated S-Meters and even a choice of db per s-unit, because a lot of the Japanese Radios use 4 db per S-unit, and the differences aren't the same over legacy radios scales anyhow.
Notice in the tested radios on that last page, that an S-0 on a KenWood TS-180 comes out at near S-3 on the standard S-unit (-108 dbm) vs -109 dbm for the standard.
Bill's answer is exactly correct. The sampled bins determine the expressed Signal level. I''ve never seen an accurate S-0, but if someone does succeed in building a noiseless receiver, it would be awesome. But I'm not holding my breath. 8^)
If someone wants their ego stroked or is trying to justify the fortune they spent on a gawky tower and antenna then make them feel better and tell them they're giving you 20+. What difference does it really make? One man's 20+ is another man's S7.
Below are some comments from the op in a previous thread on the problem:
“I have started to have a 5-7 s noise figure on 80/40 meters and a 3 s on 20 meters "with" or "without" the antenna disconnected.”
“This has just started in the last month or so. I am now unable to hear weak stations because of it.”
This isn’t a radio or S-meter interpretation issue, since it just started, the op says is now unable to hear weak stations because of the noise, and Flex ruled out any problems with the radio. So it seems to me the remaining possible culprit is local noise of some sort, which is being introduced into the radio even with antenna disconnected or shorted. My next step would be to track down the source of a possible local noise source (starting with shutting down the mains breakers and running the radio from a battery to rule out the source being in his QTH).
i am likely an older dog than you are Hi. Hi.
To explain the flex meter in simple terms. Absolute vs Relative I will explain.
Flex uses an absolute meter giving exact readings of what it is Hearing
Legacy S Meters are Relative meters giving some effectively meaningless measure of the AGC voltage. They are supposed to be calibrated to 50microvolts over 50 ohms equals S9 or -73dBm but due to the non linearity of AGC Circuits, there is no consistency of those readings even between the same models from the same manufacturers. each S unit is supposed to be 6dB but Almost none are. The Japanese typically range from 3-TO 5 dB per unit. In othewords a feel good number that is totally meaningless. if you have a Legacy S meter and you want a useful S number use your ears
For the unschooled - a politically correct way of describing the Trolls who don’t know what they are talking about but like to argue—. Yes a dummy load connected to the antenna should give you a ZERO reading BUT ONLY IF IT WERE COOLED TO -273K. BTW S0 is by definition-127dBm and does NOT mean an absence of signal SO shorting the antenna should not yield -127dBm or S0.
Think of the Flex S meter like a mercury thermometer. Mercury freezes at -38F So using it to measure -50F would give you a readings of -38F The sensitivities of Radios vary greatly by frequency. I posted some graphs several times here if you search S meters. If at say14MHz the sensitivities are -121dBm or S1, then there is no way that an absolute meter just like the mercury thermometers can or should read S0
By the way I strongly suggest you ignore the Trolls who continually moan about Flex not having a totally useless and meaningless S meter
I have compared several Flex radios this way between at least a dozen different receivers and have never found a signal I could not hear on another radio and not the Flex. Although I have found some low priced radios that people do not give credit too for their excellent receivers that on the bands receive as well as the Flex. Maybe they do not get as good results on the test instruments but they sure do when listening for weak DX signals.
Joseph, I will take your request and questions as not understanding what is happening, so this "Season 2 - Episode 4" of S-Meter Chronicles follows:
The Theory: 1) The front end component of a Direct Connect (directly connected to the antenna and PreAmp) SDR radio is a analogue to digital converter that captures the exact voltage as over 2,000,000 binary numbers per second (avoiding the conversion details and math involved)
2) Every A2D has both maximum (overload) and, significantly in this case, MINIMUM sensitivity levels (binary 0 numbers produced)
3) On all bands, more so as the received frequency is reduced (some at 40M and more so at lower frequencies - check this out on the BC band).
Your Case: 1) Your Maestro is set at -8db attenuation which is delivering signal to the A2D converter SIGNIFICANTLY below the MINIMUM THRESHOLD (more to follow).
2) While this is great for normal signals, you are complaining about the noise floor or very low level signals and the S-Meter reading.
3) Raise the amplifier gain and watch your "noise floor" SEEM to drop
Repeating this on my 6700:
Table of Readings at 7.000 Mhz, CW 500Hz bandpass (standard filter), No Antenna:
Preamp dbm S-Meter Delta Notes:
-8 -106 S3 N/A Noise < A2D minimum threshold
0 -119 S1 (-13) Noise level still < A2D minimum
+10 -126 S0.5 (-20 / -7) Noise level still < A2D minimum
+20 -133 <S0 (-27/-14/-7) Noise level NEAR or ABOVE A2D minimum
+30 -133 <S0 Same as above Gain now OVER minimum
This demonstrates that the REAL NOISE level is around -133dbm, <S0. The -106 level shown at 8db attenuation is STRICTLY because you have chosen to extend the A2D dynamic range in favour of sensitivity to very low strength signals.
So, if you want extreme sensitivity then raise the PreAmp until those signals are within the A2D passband. If you want more tolerance for very near stations then reduce the gain. If you want a quieter background then modify the AGC-T, likewise adjust the AGC-T to the sweet point (see other online postings) where the A2D actually expands the gain of the near noise signals.
So, yes, the S-meter is dead wrong if it shows anything but ZERO with shorted input.
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