The S meter values across the bottom of the Control Panel

PeterPeter
edited December 2019 in Problems and Issues
What is the basis of the S meter values across the bottom of the Control Panel??

It has a much more impressive reading of 2-3 S-points now than the S8-S9 shown by my FT-857 right now.
These are both on almost the same freq. and are looking at the noise in the passband.

And this looks to be a constant relationship with a +/- 1 indeterminancy.

Comments

  • G8JNJG8JNJ
    Hi Peter.

    The FT-817/857/897 series have very poorly calibrated S-meters.

    The first few S-points are less than 1 dB per division apart.

    https://g8jnj.webs.com/SMETER.pdf

    Regards,

    Martin - G8JNJ
  • jksjks
    On the "config" tab of the admin page (e.g. my_kiwi:8073/admin) is a field called "S-meter calibration (dB)". You can change that value and make the S-meter match your FT-857 if that's what you want. The -13 dB default value gives correct S-meter readings when a decent signal generator (e.g. hp 8657) is hooked directly to the SMA input. Others have reported similar results (I think Glenn said he needed -14).

    Of course what the S-meter value actually means when connected to a real antenna is an argument as old as radio itself..
  • n6gnn6gn
    Based on half a dozen Kiwis, I think the "-16" 'factory' number is pretty close. I don't recommend setting it to 'match' the Yaeasu or another radio because, as Martin says, that radio and many/most others are likely only correct at one point - often they set S9 to be -73 dBm with any preamp off. Not only are the S units not 6 dB each (there's a school of thought of which I'm not a member that thinks they should be 3 dB) but they are not uniform across the meter's range. And, except for newer radios particularly SDRs, the S-meter calibration is not adjusted to be referenced to the input connector between preamp on and off settings.

    I've heard it suggested that this has been done deliberately by manufacturers in order to make make their radios seem more "sensitive". But if so, I think it has been a terrible disservice because it hides the absolute signal and noise levels such that real problems aren't recognized and addressed. A receiver with an S meter that is accurate and can be calibrated and trusted for both signals levels and RMS noise in a known bandwidth, as the kiwi can, is a great boon to all of us, IMO.
    I suggest using the kiwi to measure/calibrate the commercial radio and keeping the results handy so that useful values can be obtained.
  • PeterPeter
    First to Martin
    I think the divisions could be as small as 0.5dB!!
    I rather thought this with the FT-857 was so, very similar to the FT-290R. LA8AK had a very good mod for the S-meter cct in that rigo.

    JKS - I won't be adjusting to match the FT-857. It so happened I moved the the 857 to the same room as the KiwiSDR and was surprised at the differences.

    N6GN - So you and I are '6dB' people. The stories about different S-meters and their 'calibration' have been replayed time and time over the years, and won't be regularised anytime soon.
  • WA2ZKDWA2ZKD
    https://en.wikipedia.org/wiki/S_meter
  • WA2ZKDWA2ZKD
    Yaesu AGC and S-meter readings have a history. I have had a few of their rigs and the older stuff seemed like the AGC drove the S-meter, and little else. Surely the IF/audio gain was not well controlled. The gain controlling has gotten better but maybe the S-meter still needs refinement!
  • Thos1087Thos1087
    When the S Meter option is selected can we have a readout in S points as well as db - This would be more user friendly.
  • G8JNJG8JNJ
    >
    >When the S Meter option is selected can we have a readout in S points as well as db - This would be more user friendly
    >

    I think it would make the text too small to be useful and it's very easy to quickly read S points from the bar graph anyway.

    Personally I'd ban 'S' points as they are pretty meaningless, but that's just my opinion :-)

    Regards,

    Martin - G8JNJ
  • WA2ZKDWA2ZKD
    S units have been so misused over the years by the OEM, even when they are accurate they often get ignored. I prefer dBm myself!
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