R&S 1129.7246.03, Operating Manual

Page: 126 / 855

Operating Manual 1302.6163.12 - 03 4.95
R&S ESU Instrument Functions
APD Mode
4.7 APD Mode
With Firmware Version 4.13 of R&S Test Receiver ESU series a new CISPR
weighting function is available for measuring the Amplitude Probability Distribution
(APD) of a disturbance signal.
This new measuring function was introduced by Amendment 1:2005 to CISPR 16-1-
1:2003. In this standard the APD of a disturbance signal is defined as:
"The cumulative distribution of the probability of time that the amplitude of distur-
bance exceeds a specified level".
In R&S Test Receiver ESU the APD is measured at the output of the envelope
detector. The APD measurement method gives all amplitude probability information
taken over the entire disturbance envelope within the measurement bandwidth at a
certain frequency within a specified time interval, i.e., it provides a statistical charac-
terization of the disturbance signal in question.
Fig. 4.27 Block diagram of APD measurement circuit with A/D converter [ 1 ]
The amplitude of the disturbance is expressed in terms of the corresponding field
strength or voltage at the receiver input. The method of measuring the probability of
time pmeas during which the disturbance envelope exceeds a specified level Elimit
is applied. Usually, an APD measurement is carried out at a fixed frequency.
Advantages of the APD measurement method:
• Is expected as an alternative method to present logarithmic average
measurements.
• Con also be used to calculate the true average value.
As an alternative to the latter, state-of-the-art spectrum analyzers with a wide
dynamic range (>70 dB) can be used to measure the true average value directly.
Background material on the application of the APD-measuring function is provided
in [
2
]
1. Amendment 1:2005 to CISPR 16-1-1:2003 (1st Ed.): Radio disturbance and immunity measuring apparatus - Measuring apparatus
2. Amendment 1:2005 to TR CISPR 16-3:2003 (2nd Ed.): Correlation between amplitude probability distribution (APD) characteristics of
disturbance and performance of digital communication systems