Front Panel Operation
Manual 31470, Rev. E, April 2001
2-35
2.3.14
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 8650A 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 8650A 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 8650A may lose sync are listed in the following Sections 2.3.15 and 2.3.16
and also in the minimum pulse width specifications in Section B.2.2 for the modulated sensor
used.
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Summary of Contents for 8650A Series
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Page 228: ...Series 8650A Universal Power Meters B 12 Manual 31470 Rev E April 2001 ...
Page 240: ...Series 8650A Universal Power Meters Index 6 Manual 31470 Rev E April 2001 ...