Stated first that we can survive without accurate S meter readings and
better we use something else to measure strenghts than communications
receivers, the point that's difficult to use the modern receivers AGC
line in order to properly drive an S-meter divided into S-units is a
bit pessimistic in the digital era.
Whatsoever it is the actual AGC line response to the incoming signal
amplitude, one of the several microprocessors inside a modern RX can
perfectly be programmed to do (among many other stupid functions) the
rough correction of the derived AGC voltage in order to drive a
logaritmic metering circuit that follows the choosen dB/div and
indicates an "S9" when 50uV are present on the antenna socket.
73,
Mauri I4JMY
> ---------- Initial message -----------
> 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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