Giga-tronics 8650A Series, Operation Manual

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Front Panel Operation
Manual 31470, Rev. E, April 2001 2-27
though the filter settling time has been set to a long time constant of 2.56 seconds, the update rate of
the meter will be much faster, and even the first reading will be very close to the fully settled value.
PAP Mode
The Pulse Average Power (PAP) mode is similar to the MAP mode, but it measures pulse-modulated
signals having a known duty cycle. You can specify this duty cycle and the 8650A will automatically
correct the measurements so that the displayed readings indicate the peak RF power during pulse ON
periods.
For example, when measuring a pulse modulated signal with 50% duty cycle, MAP mode would give a
reading 3 dB lower than the reading that would be given by PAP mode with the duty cycle factor set to
50%.
BAP Mode
The Burst Average Power (BAP) mode measures the average power during an RF burst
(see Figure 2-16). This mode is very useful for measurement of pulse modulated signals which are not flat
or have amplitude modulation during the pulse ON period, as in the case of TDMA (Time Division
Multiple Access) communications signals. In this mode, the 8650A recognizes the beginning and end of
a burst of RF power and takes an average of the power during that burst. The RF level can vary over a
wide range during the burst as long as it remains above a noise threshold, which is automatically
calculated by the 8650A. As soon as the RF power drops below the noise threshold, the RF burst is
complete and all further readings are discarded until the next burst starts.
NOTE:
The duty cycle correction presumes a perfectly rectangular profile for the RF
pulse shape. Any abnormality such as overshoot, undershoot, slow rise time or fall
time, inaccuracy of the duty cycle, or deviation from a flat pulse response will cause
errors in the indicated reading.
Figure 2-16: Burst Measurement
☛ ☛ ☛ ☛
Start of Burst
End of Burst
Noise Threshold
Po
w
e
r
Time