Hello Steve,
when I learned for my license at the beginning of the 70ties, I still used
to learn the old system for S 1 to S 9 reports to be judged by ear. And
that of course depends very much on the background noise and several other
factors that are completely depending on the person giving the reprot.
On LF I use a level-meter so I can read the signal strength directly in dBu
(0 dBu = 0.775 V). I calibrated this relative measurment using a one-meter
diameter loop so that I sould be able to determine strength in dB
microVolt/m within +/- 1 dB (still I am missing a couple of dB and don't
know exactly why ...). As a reference I use the (constant) signal level of
DCF39, so evem with a pre-amplifier or a different antenna I try to give
"absolute" dBu-reports for comparison purposes. But off course, if that
band is quit I can hear a station quite loed and would give it a S7 or 8
report, when the band is noisy I can barely hear a station that is 20 dB
stronger, so just by ear I would give an S3 or 4 report by ear. What I try
to do on LF is to give a subjective RST report plus the dBu value. Also on
my homepage I list the dBu values, so at least everybody can judge how
strong his signal is relative to the other stations. So I believe what you
call S-units above noise comes close to the old S 1 to S 9 scale given by
ear and reflects more the audible quality of the system than the absolute
S-value.
Best 73
Geri, DK8KW (W1KW)
http://www.qru.de
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