[600MRG] Uncalibrated S-Meter

[Frank Lotito]

In discussing the measurement of noise some of us have used the phrase "uncalibrated S-Meter."  What is an "uncalibrated S-Meter?" What makes us think that without challenge, S-Meters are unreliable, while signal strength meters reading out in microvolts or dBm are any more accurate? If for example, if S9 means 50 uV at the antenna terminal of a receiver having a nominal 50 ohm input impedance, wouldn't the microvolt readout option indicate 50 uV?  The dBM readout option indicate -73 dBm? (For those receivers where we can select the signal strength unit, S-unit, dBm, or microvolt.)

Granted, the glow-in-the-dark, heavy-iron boat anchor's S-Meter in all likely hood  has a signal strength metering circuit that lacks not only accuracy, but also "repeatability." Maybe some of the newer design solid state receives suffer the same ills?   Ditto for RF spectrum analyzers, RF level meters, RF signal generators with built-in output meters / step attenuators.

At our individual stations, repeatability is more important than accuracy. I submit even linearity is more important, e.g. each S-Unit really is a step of "X" dBm? When we compare the measurement results between stations, accuracy and repeatibility are both important. 

There are ways to determine a signal measuring device's "accuracy and repeatibility."  Can you suggest one or more methods  of doing that other than "using a calibrated signal generator that has not seen the inside of a bona-file RF calibration lab" in the past 10 to 20 years?  I don't believe we can for accuracy.  However, within the confines of our own shack, our "A" vs "B" measurements, especially when we can do the comparison by flipping a switch in a fraction of a second, should not be clouded by accuracy concerns.   

73 Frank Lotito  K3DZ / WH2XHA