Receiver sensitivity (microVolts vs "S" units)

[John Campbell]

Hello Heath Gang:

    The thread concerning receiver sensitivity and signal/noise ratio is
both interesting and enlightening. I ran across a chart several years ago
which lists the signal required (uV) and the corresponding "S" meter
readings on a properly calibrated receiver. This chart lists both the
classic "Ham" standard and the newer "World" standard. It goes as follows;

"S" units        Old Ham Standard          Newer "World" standard

S9               50.00 uV                  40.00 uV

S8               25.06 uV                  20.04 uV

S7               12.56 uV                  10.04 uV

S6               6.29 uV                   5.03 uV

S5               3.15 uV                   2.52 uV

S4               1.58 uV                   1.26 uV

S3               .79 uV                    .63 uV

S2               .39 uV                    .31 uV

S1               .19 uV                    .15 uV

   As can be seen from the above chart, if you are peaking a receiver for
operation on 80 or 40 meters, then pretty much anything below 1 uV or so in
sensitivity is unuseable. This is because the noise level on these bands is
typically S3 to S7 on most receivers, thus a perfect example of a poor
signal/noise ratio. Of course as we move on up in frequency the band noise
drops and sensitivity below 1 uV becomes more of an issue. Obviously by the
time we get up to ten meters, where band noise is minimal, we would do well
to strive for an optimum S/N ratio. The point to all of this is that as we
strive to optimize our green jewels' receive performance, it would be better
to do so on either 10 or 15 meters, then the lower bands will also be quite
acceptable in performance as the main limiting factor there is the ambient
band noise levels.

                        73........John (W8JNC)
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