Table of Contents
Advertisement
Making Measurements
Example 10: Power Measurement Functions
Making Carrier "Off" Power Measurements
Carrier "Off" power measurements are usually made under the same
conditions as are the "On" power measurements. Power-indicated
accuracy and time-averaged representativeness issues apply here also.
RMS detection is usually very important for carrier "Off"
measurements because the power tends to be noise-like. The ideal
resolution bandwidth for "Off" power measurements may be only about
the width of the spectrum of the signal to minimise the addition of noise
from the spectrum analyzer or other system noise generators. If noise is
not a consideration, a wide resolution bandwidth, such as that used for
the "On" power measurement, is preferred.
The averaging zone is like that of the "On" power measurement
averaging zone, dependent on the time between threshold crossings.
The starting point after the falling edge is delayed by 1% of the sweep
time plus about 1.2/RBW. The ending point preceeds the threshold by
1% of the sweep time plus about 0.6/RBW.
Unlike the "On" power measurement case, changing the averaging zone
using triggering is not practical. Some control may be exercised by
changing the sweep time or resolution bandwidth.
Making CHAN PWR OVER BW Measurements
The channel power function cumputes the sum of the power across the
bandwidth (centered at the center frequency) specified by the CHPWR
BW parameter. RMS detection is usually important, as previously
discussed.
The CHPWR BW parameter is the 6 dB bandwidth. This means that a
sine wave at the edge of the band (for example, a frequency given by the
center frequency plus half of the CHPWR BW) will cause a response in
the channel power measured 6 dB below the response to a sine wave at
the center frequency. Sine waves outside the CHPWR BW are rejected
by the selectivity of the chosen resolution bandwidth.
The 3 dB bandwidth of the channel power function is narrower than the
CHPWR BW by 0.6 times the resolution bandwidth. The user can
compute the desired CHPWR BW to program by adding 0.6 RBW to the
desired 3 dB bandwidth.
Spectrum Analyzer Functions Used
The carrier power measurement functions, including the on-power and
the off-power (carrier leakage), will be used to measure a burst RF
signal.
Chapter 2
127
Advertisement
Table of Contents
