AM-48 Test Set (18-0015) Measurements
0015-S08
-7
The constant K is derived by giving an undistorted signal a nominal
value of 100. Therefore:
K = 2Safwo/Po
Where: Po = Peak voltage of the undistorted (original) signal
Afwo = full-wave average of the undistorted (original)
signal
Therefore: P/AR = 100 * (2(P/Po)/(Afw/Afwo)-1)
or P/AR = 100 * (2(Pn/Afwn)-1)
Where: Pn = normalized peak voltage of the received signal
Afwn = normalized full-wave average of the received signal
Factors Which Affect P/AR . P/AR is most sensitive to envelope
delay distortion and return loss problems. To a lesser degree, it is
affected by attenuation distortion, noise, and nonlinear
(intermodulation) distortion. It is basically unaffected by transient
phenomena, such as impulse noise and phase and gain hits.
Envelope Delay Distortion . There is a high correlation between
measured P/AR values and values calculated from a plot of envelope
delay distortion. In fact, for an envelope delay response containing
significant ripples, P/AR is a better indication of the ability of the
network to pass data reliably. Return loss problems are a common
source of envelope delay ripple.
Effect of Noise . Noise can have a significant effect on a P/AR
measurement. For this reason, it is important to measure signal to
noise ratio (or noise-with-tone) before making a P/AR measurement.
If the signal-to-noise ratio is less than 25 dB, the P/AR reading will
be significantly reduced by noise alone.
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