SV: [AMPS] s meter calibration

[sm5ki]

As far as I remember Ed Tilton in an old QST was the one who first suggested
S9=50uV and 6dB increase beetween the S-points. Right? / Hans SM5KI
----------
>Från: "Ian White, G3SEK" <G3SEK@ifwtech.com>
>Till: amps@contesting.com
>Ämne: Re: [AMPS] s meter calibration
>Datum: tis 13 jun 2000 06.45
>

>
>Skipp wrote:
>>
>>Had a quick look at the site...   Their amplification abuse page 
>>says 3 dB is a one s-unit change on your receiver meter.  I was 
>>under the impression receiver s-meters were calibrated 50uV 
>>for S-9  and 6 dB per s-unit.  The occasional "other mfgr" using 
>>100uV for s-9
>>
>
>50uV/6dB is an IARU recommendation, but it has little effect in real
>life.
>
>The idea of a single input level for S9 came long before modern
>transceivers, where there is a choice of 2, 3 or even 4 different levels
>of RF gain. That means the reported strength of the other guy's signal
>depends on which buttons you choose to push on the RX... which if you
>think about it is pretty absurd. 
>
>Also, the idea of a constant number of dB per S-unit assumes there is a
>linear relationship between dB gain in the IF/RF stages and the applied
>AGC voltage (which is what the S-meter actually measures). That was true
>in old tube receivers, but not with modern solid-state.
>
>According to the lab reviews in the magazines, most modern receivers
>seem to be calibrated so that the difference between S9 and S9+20 is
>pretty close to 20dB. Below S9, the scale looks linear but the dB per S-
>point is not! It typically takes many more dB to get from S2 to S3 than
>it does to get from S8 to S0 - often less than 3dB per S-point at the
>top end. 
>
>Right down at the bottom end, it's like your car speedo - there may not
>even be an S1 marking.
>
>It doesn't have to be that way - there are engineering solutions that
>could easily deliver the full IARU specification - but when everybody on
>HF is "five nine" anyway, who cares any more?
>
>73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
>                          'In Practice' columnist for RadCom (RSGB)
>                           http://www.ifwtech.com/g3sek
>
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>

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