LBXXXA Series USB Powe
™
Product Manual PMA (Power Meter Application)
Revision: 08/02/11
- 17 -
3. Connect the sensor to the RF source and turn the RF power on.
4. The GUI display should now indicate the source power at 1 GHz: ~0 dBm pulse power; ~50% DC; ~0 dBm peak;
~-3 dBm average; and ~3 dB CrF (Crest Factor is the ratio between peak and average power or PAR).
5. Vary the source power and duty cycle to see if the GUI display tracks the source.
Powe™ measurements are real time presentations of power. They are not a type of calculated measurement
made by most CW sensors. You will note a corresponding change in the duty cycle reported in the GUI if you change
the duty cycle of your source. You will note a change in the pulse envelope power (the large display), peak power, and
average power if you change the power level. The duty cycle will remain unchanged.
The LB479A can measure 350 nsec pulses at -55 dBm (and lower) with a PRF of 1 kHz (or lower). Such
measurements require averaging to be set between 5000 and 10000.
Alternate Pulse Measurement using Duty Cycle
Powe™ sensors can make the more traditional pulse measurement using an assumed duty cycle as an
adjustment to the indicated power. This type of measurement is less accurate and more prone to error because of the
pulse shape factor; and because the duty cycle is assumed. However, this a useful measurement approach
using the LB5XXA line of instruments.
The duty cycle correction is calculated as follows:
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 follows:
Pulse Power = -20 dBm + -(10Log
10
(Duty Cycle)) = -20 dBm + (10 dB) = -10dBm
The sensor must be placed in CW Power mode to access this style of duty cycle measurement.
