[AMPS] s meter calibration

[Peter Chadwick]

Question # 1: so what does it tell you as an operator if a signal is 50
microvolts or 25 microvolts in terms of real, on air operation? bearing in mind
that the noise on 80m can easily be S5 and a really good sig on 10metres fine at
S2? ('You're sounding an S9 signal, but you're only a 2 on the meter')

Question # 2: So how many transceivers have the necessary gain stability over
temperature, time and supply voltage for it to be meaningful?

Question # 3: How good is your signal generator accuracy? Hewlett-Packard as was
(Agilent now, or genitAl for those with a puckish sense of humour) rate their
generators as +/-1dB for the better ones, +/-1.5dB for the others. (Accuracy,
NOT resolution). Now that is into an accurate 50ohm load. How low is the input
return loss of the receiver, and how stable is it with time temperature et al?
>From a system point of view, how low is the SWR on the antenna?

The result of all this in the end is that the S meter reading is pretty
meaningless, and unless the receiver has known gain stability, including over
the frequency range, even the relative readings are suspect. That's why  level
measuring receivers are so pricey.

Which is why I say that the 'S' in 'S meter' stands for suspicious.

73

Peter G3RZP


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