In the real world, there isn't any . . . depends upon the make and model of
receiver and its design and the calibration and alignment of the particular
receiver.
We tend to use the 6 dB/S-unit as a convenience but it has no regulatory or
technical standing. Same situation as the "S9 = 50 uv" "standard." Both
have become urban myths based upon the calibration procedures that some
companies have used in the past.
With any given receiver, you will find variation of the S-9 calibration
point from band to band and even within a band. You will also find
variations in specific S-unit delta values over the signal range, and again
within a band and from band to band. Most amateur receivers will show more
S-meter activity at the low end of the scale - fewer dB per S-unit mark -
that at the mid and upper ranges.
Only expensive commercial and military receivers actually determine and
indicate the signal level at the antenna terminals and/or have scales
calibrated in software to deal with in-band and band-to-band calibration
variations.
There is probably nothing wrong with using the informally defined "S Unit"
of 6 dB as a convenient measure, but one should not expect any amateur
receiver to possess that actual calibration within and over all bands.
73/72/oo, George W5YR - the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121 Kachina 505 DSP #91900556 Icom IC-765 #02437
Mark Erbaugh wrote:
>
> The Pegasus Programmer's Reference Guide (PRG) says that the signal strength
> query returns results that represent S-Units (and fractional S-Units). This
> makes it pretty easy to display signals up to S-9, but what about signals
> stronger than S-9? Most people expect a meter calibrated in db over S-9. I
> designed my display assuming 6 db / S. Thus S10 would be 6db over S9, S11 12
> db over S9. S13 18 db over S9, and so on. While I don't have radios setup
> for side by side comparisons, it seemed that the strong signals on 75 were
> reading higher with this display scheme than I saw on other radios.
>
> Then today, I'm reading a 1296 MHz antenna review in the latest QST and the
> author says the signals went from S3 to S8, an increase of 15 db. That's
> only 3 db per SUnit.
>
> So, just what is the relationship between db and SUnits?
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