Bird Technologies VPM3 - Manual (Page 35)

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Burst average power is calculated in the 7022 automatically using the average
detector and the duty cycle.
Burst average power can also be calculated in the time domain mode using the
average power between markers function.
Burst power measurements provide accurate, stable measurements in bursting
applications such as TDMA and radar. Accurately measuring the output signal
strength is essential for optimizing radar coverage patterns. Actual transmitted
power in a single timeslot can be deter-mined in TDMA. The other timeslots
must be off during this test.
Figure 23 Burst Average Power
Crest Factor
Crest factor (CF) is the ratio of the peak and average powers, in dB. The WPS calcu-
lates the Crest Factor from the Forward Peak and Average Power measurements.
Crest factor is becoming one of the most important measurements as communi-
cation systems move into the digital age. For CDMA and similar modulation
types the CF may reach 10 dB. If the crest factor is too large, the transmitter will
not be able to handle the peak powers and amplitude distortion will occur. Crest
factor can also detect overdrive and overshoot problems. Knowing the CF allows
end-users to more accurately set base station power and lower operating costs.
Figure 24 Crest Factor, 10 dB CDMA Signal, 100 W Peak, 10 W Ave
Complementary Cumulative Distribution Function (CCDF)
CCDF measures the amount of time the power is above a threshold. This thresh-
old is set in the Configure, CCDF Factor menu. Equivalently, it is the probability
that any single measurement will be above the threshold. The WPS samples the
power over a 300 ms window and compares it to a user-specified threshold, in
Watts. The time above the threshold relative to the total time is the CCDF.