[Help] Swan-500C S-meter sensitivity issue

Discussion in '"Boat Anchor" & Classic Equipment' started by HL4SF, Jul 19, 2012.

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  1. HL4SF

    HL4SF Ham Member QRZ Page

    Hi there,
    I have a Swan-500c with a low sensitivity S-meter.
    I did the zero point adjustment as the manual said but It indicates 4~5 S-unit less than my IC-746.
    Can you advice me what to do to fix this issue?
    Thanks and 73.

    Wonki, hl4sf...
     
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    SF:

    The Swan unit almost certainly has a meter sensitivity calibration of 50-microvolts = S-9 whereas the IC-746 almost certainly has the "S" meter set for a much lower signal strength for S-9. A while back the various Japanese manufacturers got into a "war" claiming that their receivers were more sensitive than the other manufacturers. However, all that they did was to decrease the signal strength needed for an S-9 reading as well as for the "dB over" readings. As such, the "S" meter readings don't really mean anything!

    With a sensitivity of 50-microvolts for S-9, you need 500-microvolts for a "20 over", 5000-microvolts for a "40 over", and a whopping 50,000-microvolts for a "60 over" reading. All of my "S" meters are calibrated for S-9 = 50-microvolts and I do have a better than average antenna installation. Seldom do I get a reading of "20 over" on a signal and "40 over" almost happens on signals from stations that are just a few blocks from me. In fact, many times the "S" meter reading on other stations doesn't even make an S-9! However, I hear "40 over" and even "60 over" readings being given to stations because of the calibration on many "modern" meters.

    The "S" meter readings are completely meaningless! What really matters is the signal to noise ratio of the signal. A signal that doesn't even read on the "S" meter is perfect copy when the noise level is low and a signal that barely reads above S-9 on the meter is difficult to copy when the noise level reads S-9.

    Basically, don't worry about what the "S" meter reads! Use the "olde tyme" method of giving signal reports (which was in use for decades before "S" meters became common on receivers). If the station is perfect copy, then they are a "59"!

    Glen, K9STH
     
  3. WA7KKP

    WA7KKP Ham Member QRZ Page

    I remember the Swans were very liberal when it came to S meter readings on receive. And Drakes were very stingy . . .

    As Glen says, unless there is a standard calibration point, they really don't mean much. Unless you can get a calibrated sig gen and measure how many microvolts it takes to get to s-9, and other points above and below. You'll discover that s meters rarely respond in a logrhythmic fashion.

    Gary WA7KKP
     
  4. KO6WB

    KO6WB Premium Subscriber QRZ Page

    I have the same problem with both my Kenwood rigs. A TS-50S and a TS-590S. it seems like both of them are really hard to get the s-meter moving like other units made by ICOM and Yaesu.
    I just received an Elecraft XG-3 signal generator and the first thing I did was put the signal to my rigs. To my surprise both responded exactly the same. For S-9 it took 50uV and that number held on all bands. Increase the signal 40db and it was 40 over. So someone is still trying to meet the standard or I just got lucky and have the two different models that read exactly the same at that level.
    Yes there are companies that think the s-meter reading is all important to the everyday amateur and I would guess their marketing research has proven this to be mostly true. Their sales indicates this to be mostly true.
    So if you have a few extra bucks and want some place to spend it, I would recommend the simple little XG-3.
    Have fun
    73
    Gary
     
  5. KH2G

    KH2G Ham Member QRZ Page

    Lots of good and true answers here but I think we need to be aware that SINAD is the norm for today. As a refresher for those who forgot =
    The SINAD figure is expressed in decibels (dB) and can be determined from the simple formula:SINAD = 10Log ( SND / ND )where:
    SND = combined Signal + Noise + Distortion power level
    ND = combined Noise + Distortion power level
    It is worth noting that SINAD is a power ratio and not a voltage ratio for this calculation.
    Regards,
    Dick
     
  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    LDS or MDS (least discernible signal / minimum discernible signal) is a better measurement of sensitivity than SINAD or "20 dB quieting" for non FM receivers. The LDS/MDS is measured by reducing the input until the signal can just be detected by the human ear.

    On HF, the inherent band noise is virtually always greater than the LDS/MDS of a receiver so absolute minimum signals are lost in the band noise. On VHF, UHF, and higher frequencies, having a very low LDS/MDS is important because of the very low noise level that is on these bands. Of course, man made noise (i.e. computers, switching power supplies, etc.) are contributing to higher noise levels on the higher frequency bands and noise in many urban and suburban areas is now becoming a problem.

    Glen, K9STH
     
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