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S-Meter Accuracy of FLex and Others - Rob Sherwood

HCampbell  WB4IVFHCampbell WB4IVF Member ✭✭

With all the recent (and not so recent) posts on the Flex
S-meter and its calibration, you might find Rob’s take on the subject interesting: 

  Rob Sherwood on “S-Meter Accuracy” 6-OCT-2016

While no Japanese rig has a properly tracking S meter, the following do:

  Flex 6000 series

 Apache ANAN

 Most K3 and K3S, though occasionally an individual radio cannot be calibrated properly. This includes the option to have the reading correct regardless of preamp or attenuator setting.

 Orion II once Ten-Tec updated software to allow S meter calibration. Orion II does not correct for preamp or attenuator selection.

 Eagle is good, except the S meter is microscopic and I think it quits at S9+30 dB. The Eagle reads correctly regardless of preamp or attenuator selection.

 Hilberling S meter is quite good.

 ADAT ADT-200A is very good but ergonomics in general are absurd.

 Elad DUO S meter is outstanding

 Perseus S meter is outstanding.

 With virtually all current products today having a virtual S meter, there is no technical reason the S meter cannot be programmed to read properly from S1 to S9+60 over.

When an S unit is only 2 to 3 dB, it makes QSB look much worse.*

Rob, NC0B

-------------

*Note (by DJ0IP): Most recent Japanese transceivers are using just 3 dB per S-Unit. This makes the received signal look stronger... but at the same time, the QRM, QRN, and QSB also look worse!

http://www.dj0ip.de/sherwood-forest/sherwood-sound-bytes/


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Comments

  • Jim GilliamJim Gilliam Member
    edited October 2018

    I am not sure that the Flex S-meter adheres to the accepted standard of an S-meter. I believe the accepted standard is that the S-meter should register the highest peak that exists with the bandwidth of the received signal. Roughly to me, it appears the Flex S-meter integrates all frequencies within the passband and provides a reading. I am not sure which method is better.


    Jim, K6QE


  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited April 2019
    @Jim

    Traditional S-Meters circuits were designed to INTEGRATE A 500HZ passband not peak In fact NONE of the Japanese radios do either
  • Bob - W7KWS -Bob - W7KWS - Member ✭✭
    edited October 2018
    For me, the accuracy of an S-meter's calibration is useful for testing but is over rated and over used for communications purposes. To me, S-meter accuracy is of little value on any manufacturer's radio. Any relative indication of signal and noise strength is all one needs for letting the other station know if you can copy them. The meter reading is more an indication of the path. The station is a factor but only a small part of the equation at best with propagation being, by far, the dominant factor. It seems to me that absolute S-meter readings are used most often these days to feed the ego of the person on the opposite end of a QSO and does little to help the distant station make adjustments such as turning on the AMP or rotating the beam, Etc. So often I hear "you're rig is doing a great job. 30 over here", when it's the propagation that was contributing the most to the meter reading and QRP would have been entirely adequate. You've probably heard the old adage that I worked that station with a wet noodle. In other words, propagation was great and the main reason for the success of the contact. In reverse, the same "he-man" kilowatt station is received with an S-9 meter reading but a local noise source is also S-9 so the communications is marginal or non-existent. What did the S-meter reading tell the distant station in either of these two cases? In my estimation, nothing of real value. For me, the real indication of signal value is the signal to noise ratio. In other words, the signal strength above the total noise strength in the receiver pass band. Any somewhat linear relative strength meter will give you these values, calibrated or not. This SNR, communicated to the the distant station, versus an S-meter reading, is a much better indication of your ability to copy the intelligence being transmitting. No egos involved!
  • Jim GilliamJim Gilliam Member
    edited October 2018

    Is that 500 Hz. bandwidth of sampling for 0 to 500 Hz. or some where in between. It would seem if the latter were true, a person with a low voice response would register higher on the S-meter than one with a higher pitched voice.
  • KF4HRKF4HR Member ✭✭
    edited November 2019
    Accurate or not, if there were no S-meters, what in the world would some of the guys on the night time 80M nets have to talk about?!  Just funnin'... 

    I've always been under the impression that an S-unit was somewhere in the 5 or 6 db range, but it would make sense that some manufacturers might want to boost sales (and ego's), and use 2-3 db per S-unit. 
  • Burt FisherBurt Fisher Member ✭✭
    edited November 2019
    I'll make it simple when the receiver has a dummy load for an antenna I want it to read zero on my 6400M like on my KX3 and formally on my 7300.  Currently it read S7 on 80 meters on the 6400M and slightly lower on other bands.
  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited October 2018

    @Burt

    What you are asking for is that the S-Meter Read a TOTALLY MEANINGLESS IRRLEVENT NUMBER...which while it gives you great comfort that there is no external signal on the terminals is not related to anything that the radio may actually be hearing.


  • Burt FisherBurt Fisher Member ✭✭
    edited October 2018
    How could the radio be hearing anything when I have a dummy load for an input?
    My power meter reads zero if I turn the power down to zero, that is nothing going out, zero, so nothing coming in should be zero.
  • Bob - W7KWS -Bob - W7KWS - Member ✭✭
    edited October 2018
    Thermal noise in the front end of the radio?
  • James Kennedy-WU5EJames Kennedy-WU5E Member ✭✭
    edited June 19
    Flex good job on my FLEX 6600 S-Meter , it may seem strange I kept a log from 6500 to now on FLEX 6600 on S-meter reading I would change the normal 59 reading in AC LOG to the actual reading from the FLEX Smart SDR screen. One Ham said I'm only S-9+10 I'm running 1500 watts I discounted him as a rookie with deep pocket. well don't shoot me for that statement. hi hi . ... 
  • Bill -VA3WTBBill -VA3WTB Member ✭✭✭
    edited October 2018
    All radios have internal noise, the flex is simply reporting the signal in the Receiver bins,  sampling..coverting that noise to RF and sending that to the meter. So yes the radio hears internal noise.
    Steve Hicks has writen so much on this explaining all this and yet so many still can't get their heads around the technology.
  • KC2QMA_JohnKC2QMA_John Member ✭✭
    edited May 2019

    The only way to make everyone happy is to have in the software a way to switch from a “True S-Meter” the way it is now on the flex or “Relative S-Meter” the way old radios S-Meters work.

    I personally like the way the S-Meter works on the Flex Radios because it is truly accurate, S9= 50uV @50 ohms at the antenna connector if my memory is correct?

  • Matt NQ6NMatt NQ6N Member ✭✭
    edited October 2018
    I think this is true. It could be a Flex feature or someone could write it using the API and make a "traditional s-meter" available as an application that could be run alongside SmartSDR. 
  • Bill -VA3WTBBill -VA3WTB Member ✭✭✭
    edited October 2018
    Never thought people would be upset having an accurate meter...lol
  • Jay NationJay Nation Member
    edited October 2018
    Seems that being wrong is more popular than being right these days!

        #FlexRadio IRC chat

    For real-time discussions

            SDRgadgets

    User created documentation.
               Volunteer!!

             73, Jay - NO5J

  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited October 2018

    @Burt


    The S-Mater is reading the actual receiving level at the radio's antenna,


    This may be hard to get your head around on...

    But I will try to explain.


    If your radio on 20M is capable of a Minimum Discernible Signal of say -115dBm then it should be reading S2 (-127dBm plus 2x6dBm - 115dBm)... If you short the antenna, it still can't hear any better than S2.. so reading an Arbitrary S0 is absolutely meaningless because its not hearing S0 but it is hearing S2.

    In fact, if the shorted across the antenna were perfect and it was really cold (like absolute zero)  then the true number should be -143dBm  or  MINUS S2.5

    The Japanese Radios copied the Old AGC Voltage Circuits to give an arbitrary S Meter reading... so if you shorted the antenna, you got 0 AGC voltage and it displays as S0  - which of course is absolutely meaningless... except that it feels logical even if it is not...
  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited October 2018

    I would label the Relative S Meter as the Bu** SH*$ meter
  • Bob - W7KWS -Bob - W7KWS - Member ✭✭
    edited October 2018
    I can hear it now! "You're S-9 plus 20 dB on my Flex. To understand what I'm telling you, go to www.flexradio.com and download the manual. Note that I've selected S-meter option 47. From this, use your scientific RPN calculater to determine what 20 over means with option 47. You'll still have a meaningless indication of what I'm hearing because I've not yet told you the band noise level at my station. GOOD LUCK".

    73 & LOL!
  • AA0KMAA0KM Member ✭✭
    edited October 2018
    There is always Atmospheric noise and local generated electrical noises  around and flexradio reports it.

    Tuff to understand I guess.


    I might add have fun and connect your ground to your center pin of the pl-259 and out
    to the ground rod.

    You will be amazed at the local noise. This being I live in the city. YMMV.

  • Ross - K9COXRoss - K9COX Member ✭✭
    edited October 2018
    I used to repair CB radios in the late 60's. I would change the screen drop resistor on the final and on occasion the cathode resistor. Also would adjust the S meter for lots of deflection...I was a hero
  • edited October 2018
    Maybe we could debate "over & out" being a paradoxical phrase that John Wayne would have used in the movies - but is something that would never be used in real ACP-125 tactical procedures.

    Sorry Paul - couldn't resist. :-)
  • KC2QMA_JohnKC2QMA_John Member ✭✭
    edited October 2018

    Lets call it the "Feel Good Meter"

    It might make you feel good but it's still meaningless.

  • edited October 2018
    Roger out.
  • Michael CosloMichael Coslo Member
    edited October 2018
    Wait... do y'all people actually look at the S-Meter?  I tell everyone I like that they are 20 over 9.  Then they like me!image
  • Ken - NM9PKen - NM9P Member ✭✭
    edited June 23
    Most of the time when I hear a station giving reports like "You are S9+30" when I only hear them at S8, I can be sure that they are using about 30 dB of preamp on a rig that doesn't compensate its S-Meter.  Especially since I only run 100 Watts!

    Back in my "CB Days" (1972-74) I used to watch guys turn on their external preamp and exclaim "Look at how much more powerful this makes my radio!  It brought my noise up from S3 to S7!  Now I can hear everything!"  Then they would complain about their darned neighbor down the road who was splattering 15 channels wide.  They never understood that they were their own worst enemy by running a preamp that overpowered their receiver.  But then again, sometimes that neighbor was driving a sweep tube amp well beyond saturation with an AM signal and really WAS 15 channels wide!
  • Jay NationJay Nation Member
    edited October 2018
    For accuracy I sometimes tell them they are 21.599 dB over 20. I suspect they don't really care for that much accuracy.

        #FlexRadio IRC chat

    For real-time discussions

            SDRgadgets

    User created documentation.
               Volunteer!!

             73, Jay - NO5J

  • Stan VA7NFStan VA7NF President Surrey Amateur Radio Communications Member ✭✭
    edited October 2018
    I like to just lean back and enjoy these conversations, particularly s-meter ones.  Let's see:
     - The Flex S-Meter accurately measures the voltage at the antenna connection but the various authors don't like the accuracy, they want the old inaccuracy.  It also ignores antenna gain and external pre-amps.
     - The dx/contest station cannot be clearly heard but still 5-9 or 5-9-9.  I'm a contester and guilty as charged.  The log needs a number and convention is fill it with a default, even N1MM pre-fills with 599. 
     - And now: "Connect to a dummy load and there is still noise."

    On that last one, consider the radio chassis is the other half of the antenna connection (unbalanced input connection).  That chassis is at the junction of two antennae, one the safety ground out to your power panel and ground, and the other your RF ground wire and/or any coax connected.  The centre wire may be on the dummy load but the ground has many signals; then add in the front end generated noise.
    An aside: While we are at it, lets tell those electrons to stop jumping out of orbit due to thermal activity or nearby static charges and also demand they do not create EM waves. This is obviously the fault of the Flex management and programmers not an act of nature and the basis of our hobby.

    Tongue-in-cheek but also factual (subject to future posts)
    Stan VA7NF
  • WA5GPWA5GP Member ✭✭
    edited October 2018
    I am with you Burt:
    Not caring about the mombo jumbo overly complicated math and convoluted explanations on this that and the other hearing one thing or another inside the radio. If the antenna connector is shorted or disconnected/ connected to a dummy load I want to see "0"  because that is what it is actually seeing.  No signal No reading ~:~
  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited October 2018

    NOT TRUE... Definitely NOT MUMBO JUMBO... Basic Math...

    When you short the Antenna, you are seeing the Minimum Discernible Signal that the radio is capable of receiving at that Frequency.

    S0 by International Standard Definition is -127dBm

    If your radio reads Zero when you short the antenna... then any and all S-Meter Readings on that meter are totally wrong.

    BUT if it makes you happy to see a totally wrong and totally irrelevant number suggest you buy any Japanese radio.
  • Burt FisherBurt Fisher Member ✭✭
    edited October 2018
    Every other receiver, transceiver I ever owned (S-76, Swan-240, Kenwood TS-940, Hallicrafters, HQ-145, HQ-170,  Icom 751, Icom 746, 756), from 1959 read zero or near zero with no antenna. That's what I want now  I am not interested in the purity argument. I am not interested in random electrons and holes crashing and making INTERNAL receiver noise. Although the pretty colors on the S-meter are nice let zero be zero. 

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