Giga-tronics 8650A Series, Руководство по эксплуатации

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Front Panel Operation
Manual 31470, Rev. E, April 2001 2-37
2.3.16 Burst Dropout
In the BAP mode, average power is measured only during bursts. Because, in this mode, the bursts are
automatically detected by the power meter, the user need not be aware of the burst repetition rate in
order to make the measurement.
However, the BAP measurement algorithm defines bursts in a way which may be considered undesirable
in some applications. In the example illustrated below, a 3.5 ms burst is followed by an OFF period of the
same duration. During the burst, two brief dropouts occur. Normally, in BAP mode, each dropout would
be interpreted as the end of a burst; the BAP algorithm would interpret the burst as three separate
bursts, and the dropouts would be excluded from the average power measurement. As a result, the
average power reading would be artificially raised.
When the Burst Dropout feature is enabled, the BAP algorithm is modified so that a dropout of
sufficiently brief duration is not interpreted as the end of a burst. In the example below, dropout time is
specified at 350
µ
s. The two dropouts, which occur during the burst have a duration of less than 350
µ
s;
therefore the entire burst is interpreted as a single burst, and the dropouts are included in the average
power measurement. The 3.5 ms OFF period following the burst is interpreted as the end of the burst,
because it exceeds 350
µ
s in duration.
This feature must be configured and interpreted with care. The dropout time is selected from a series of
discrete values (.030 ms, .059 ms, .089 ms, and so on up to 3.747 ms); however, these are only the
guaranteed minimum values. In practice, the BAP algorithm may tolerate dropouts up to 2.15 times as
long as the minimum value. Therefore, the time between bursts must be at least 2.2 times as long as the
selected dropout time (because, if the time between bursts is less than the tolerated dropout time, the
BAP algorithm never recognizes the end of a burst, and the signal is simply averaged, as if the MAP
mode had been selected). Also, dropouts occurring at the end of a burst are a problem, because the BAP
algorithm cannot distinguish them from the end of the burst itself; there should be at least 250
µ
s of
burst remaining after the last dropout within that burst.
Figure 2-21: Burst Dropout
Burst Dropout
(Dropped Time = 350
µ
s)
350
(dropout time)
245
µ
s
Dropout
280
Dropout
Time
P
ower
Burst definition covers this
entire time period, including
the two dropouts because
they are <350
µ s
Burst definition does not
cover this 3.5 ms period
because it exceeds 350
µ s
µ
s
µ
s