Making The Output Power Measurement; Purpose; Measurement Method - Agilent Technologies ESA-E Series Measurement Manual

Making Bluetooth™ Measurements

Making the Output Power Measurement

Making the Output Power Measurement

Purpose

Output power measurements are performed to ensure power levels are high enough
to maintain links, yet low enough to minimize interference within the ISM band
and to maximize battery life.

Measurement Method

The power measurements covered by this test are average power and peak power
for the specified channel or center frequency. The analyzer is set to zero span mode
with a sweeptime dependent on the packet type being measured. When the
analyzer is triggered, it makes a sweep over the duration of the burst.
The peak power is calculated as the highest point in the burst.
The average power is calculated as the average power over 20% to 80% of the
burst duration. You can choose between two methods to determine the burst
duration:
1. The position of p0 can be used to define the start of the burst, or
2. The burst duration is taken as the time between the leading and trailing 3 db
points compared to the average power.
The average is calculated by converting each trace element amplitude from dBm
into linear power, adding these together, then dividing by the number of trace
elements included in the average. The final result is then converted back into
logarithmic form (dBm) for display.
For averaged measurements, the user may specify the number of sweeps over
which to average the result. This means that for an average number of 10, the
power results are obtained from each trace, converted to linear power, and then
averaged with the previous average result before being displayed. The running
average count and the log of the true averaged linear power will be displayed after
each measurement sweep.
Figure 3-2 illustrates power and timing characteristics of a signal burst in the time
domain.
Chapter 3 17