Series 8650B Universal Power Meters
2-38
Publication 31470-001, Rev C, November 2, 2017
2.4.14
Burst Signal Measurements
In a burst signal, the RF is pulsed on and off (i.e., pulse modulated). Often, the RF is modulated during the pulse
on time. Typical examples are TDMA digital cellular telephone formats such as NADC, PDC, and GSM. These
formats and many others produce amplitude modulation of the RF during bursts.
Two types of power measurement can be made on these types of signals. If the total average power is desired,
MAP mode should be used. Total average power includes both the off and on time of the pulses in the
averaging. Often it is desired to know the average power just during the bursts. BAP mode makes this type of
measurement very easy. The procedure is as follows:
1.
Calibrate the sensor according to the procedure outlined earlier in this section.
2.
From the Main Menu press
[Sensor Setup]
. From the Sensor Setup menu, press
[Modulated Sensor]
and
then select the BAP mode by pressing
[BAP]
.
3.
Press
[FREQ]
and enter the operating carrier frequency.
4.
Connect the sensor to the burst signal source and record the power level.
The 8650B will automatically find the portions of the signal which are in the burst and include only those
portions in the average.
Burst signals can have a high peak power-to-average power ratio depending on duty cycle. This ratio is
proportional to the duty cycle and is given by:
This assumes no modulation during the burst. Modulation during the burst will increase this ratio by its own
peak-to-average ratio. Due to this characteristic of burst signals, care must be taken to keep the peak power
below the maximum rated input power of the sensor.
NOTE:
If the burst average power is too low or if the bursts on time or off time between the bursts are
too narrow, the 8650B may lose sync with the bursts and fail to display the burst average power. When
this happens,
NoSync
will flash on the screen to the right of the sensor power units, and the meter will
display total average power as in MAP mode. The conditions under which the 8650B may lose sync are
listed in the following Sections 2.4.15 and 2.4.16 and also in the minimum pulse width specifications in
Section B.2.2 for the modulated sensor used.
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