Tektronix PSM3000 Series, User Manual

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Power Meter Application
Make a Pulse Measurement Using Duty Cycle
This method of measuring average pulse power is available with all instrument
models. However, this is the only method for measuring average pulse power on
PSM3000 series instruments. This measurement uses an assumed duty cycle as an
adjustment to the indicated power. This type of measurement is more prone to
error than the signal processing pulse power measurements available on PSM4000
and PSM5000 series instruments. However, this a useful measurement approach
when using PSM3000 series instruments.
The duty cycle correction calculation is:
Pulse Power = Measured Power + Duty Cycle Adjustment
The duty cycle adjustment is:
- (10log
10
(Duty Cycle))
For instance, if you measured an average power of -20 dBm and assumed a duty
cycle of 10% (0.10), then the pulse power would be calculated as:
Pulse Power = -20 dBm + -(10log
10
(Duty Cycle)) = -20 dBm + (10 dB) = -10dBm
NOTE. The instrument must be in CW Power mode to access this method of duty
cycle measurement.
To set the instrument to measure average pulse power on a signal with 10% duty
cycle, do the following:
1. For PSM4000 and PSM5000 series instruments, click the Pulse/CW button
on the toolbar to activate CW mode. You can also enable CW from the
Measurement menu.
NOTE.
For PSM3000 series instruments, the software is always in CW mode,
so the button is not available.
2. Click Offsets & Response > Duty Cycle > Setup .
The Measurement Duty Cycle dialog box opens.
3. Enter 10.0 (the duty cycle percentage), and click OK .
4. Click Offsets & Response > Duty Cycle > Enabled .
The software shows source pulse power in the CW con fi guration, and the
DC annunciator activates. You can use the duty cycle pulse power method
down to approximately 0.1%.
28 RF and Microwave Power Sensors/Meters