Bird Technologies 5012 - Manual (Page 5)

Peak Envelope Power
Peak power measurements detect amplitude changes as a signal
modulates the carrier envelope. The WPS operates in an asynch-
ronous cycle: 300 ms of waveform sampling followed by a 50 ms reset
period. The peak power is then displayed and the cycle repeats. The
display therefore updates about three times per second.
Transmitter overdrive can be detected with peak measurements.
Common problems are overshoot at the beginning of burst packets,
amplitude modulation, and excessive transients. These damage
system components with excessive peak power and also cause data
degradation, increasing the Bit Error Rate. For TDMA applications,
Peak and Burst Power measurements are used to detect overshoot in
single timeslots. Other timeslots must be turned off for this test.
Burst Average Power
Burst width (BW) is the duration of a pulse. Period (P) is the time from
the start of one pulse to the start of the next pulse. Duty cycle (D) is
the percentage of time that the transmitter is on. To calculate the duty
cycle simply divide the burst width by the period (D = BW / P). Low
duty cycles mean that the burst width is much less than the period; a
large amount of dead time surrounds each burst. For low duty cycles,
the burst average power will be much larger than the average power.
After peak power is measured, a threshold of ½ the peak is set. The
sampled power crosses that threshold at the beginning and end of
each burst. The time between crossings is used to calculate the duty
cycle. Burst Average Power is calculated by dividing the Average
Power by the Duty Cycle.
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 3
Burst Average
Power
Average Power
Burst Average Power
Peak Envelope Power
0 W
100 W
50 W
Burst Width
Period