[TenTec] Signal Strength

[Ken Brown]

The RST system was devised when many, if not most, receivers did not 
have an S meter. The S part of RST is not directly related to an S meter 
reading,although it may be "somewhat related". The S stands for anything 
from "Faint signals, barely perceptable" for S=1, to "Extremely strong 
signals" for S=9. When the noise level on the band is really low, a 599 
report could accurately and honestly be given to a signal that does not 
move the S meter above S1 or S2. On a noisy day, a signal with the same 
signal power at the receiver antenna input, might accurately be reported 
as 339. And of course, in a contest, you might hear something like "RST 
599 PSE AGN UR CL ES QTH" which means your RST is something like 339.

Even if you could calibrate your S meter for exactly 50uV at S9, and 
make the circuitry (or firmware) keep each S unit exactly 6dB and each 
dB over S9 mark exactly correct,  there would likely be some gain drift 
with ambient temperature in your receiver. Even the best commercial or 
communications receivers are not laboratory grade signal strength 
measuring instruments, and they were never intended to be. Instruments 
which are intended to accurately measure signal levels almost always 
include a built in calibration source, which is used to check and/or 
adjust the instrument calibration, before making an accurate 
measurement. I have never seen an amplitude calibrator built into a 
communications receiver (although I have seen many frequency calibrators 
built into receivers) and so would never expect a super accurate signal 
strength measurement from a receiver.

DE N6KB