Keysight V3500A, Руководство пользователя

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RF Measurement Basics 4
V3500A User’s Guide 89
Since the power is constant over the interval
T
1
, and since
the power is zero over the remainder of the interval
T
1
, the
average and peak power of pulse modulated signals are
related by the equation:
where
T
1
is the pulse width of the signal.
T
2
is the period of the waveform
In decibels, this would be expressed as:
Measurement accuracy
Mismatch error
Mismatch error is one of the primary factors affecting power
measurement accuracy. The goal is to measure the power
that a source will deliver into a load of impedance
Z
0
. The
power meter is designed to have an impedance as close as
possible to
Z
0
. Since its impedance is not exactly Z
0
, the
power delivered to the meter is not exactly equal to the
power delivered to a perfect load.
Deriving the equations to calculate the mismatch error is
beyond the scope of this document, but the results can be
easily understood.
Consider the setup in Figure 4- 4 . A source of output
impedance Z
g
is connected to a load of impedance Z
l
.
P
peak
T
2
T
1
-----
P
avg
=
P
peak dB ,
10
10
log
×
T
2
T
1
⁄ ( )
P
avg dB ,
+ =