Giga-tronics 8650A Series, Operation Manual

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Series 8650A Universal Power Meters
2-26 Manual 31470, Rev. E, April 2001
2.3.6 High Power Level Measurements
High power amplifiers and transmitters can damage standard sensors. Use only high power sensors to
measure these devices without using attenuators and measurements.
For example, if the output of an RF source is amplified to +30 dBm (1 Watt), this signal cannot be
measured directly using a standard sensor because the sensor’s maximum input level is +23 dBm (and
any level above +20 dBm is potentially harmful to a standard sensor). The signal would have to be
attenuated, and the attenuation would have to be corrected for by means of a measurement offset.
However, if a 5 Watt high power sensor is used, any power level up to +37 dBm can be measured directly
without the use of an attenuator.
2.3.7 Modulated Measurement Modes
The 8650A series of power meters expands upon the capabilities of the previous 8540 power meters in a
number of ways. In the past, power measurements of modulated signals (pulse, multi-tone, AM, etc.)
required that the signals be attenuated to levels less than -20 dBm to avoid errors due to sensor
nonlinearity. The 8650A eliminates this restriction when used with a modulation sensor, and brings the
speed and accuracy of diode sensors to the power measurement of modulated signals. Basic measurement
procedures are presented below, along with some useful tips on how to get the most out of the modulated
measurement modes.
The modulated measurement modes are available through the sensor setup menu when the active sensor
a modulated series. The 8650A features three modulated measurement modes:
• Modulated Average Power (MAP)
• Pulse Average Power (PAP)
• Burst Average Power (BAP)
MAP and PAP modes measure the true average power of modulated and pulsed signals. PAP mode
differs from MAP mode only in that it allows you to specify a duty cycle figure, which is automatically
factored into the measurement. In BAP mode, the true average power within the pulse is measured (the
pulse pattern is detected automatically, so there is no need for you to specify the duty cycle).
MAP Mode
The Modulated Average Power (MAP) mode measures RF signals, which are amplitude modulated,
pulse modulated, or both. In the MAP mode the 8650A calculates the average RF power received by the
sensor over a period of time controlled by the time constant of the internal digital filter. The result is
comparable to measurement by a thermal power sensor.
In this mode, the 8650A measures the average power of CW and modulated signals, such as:
• AM
• Two-tone
• Multi-carrier
• Pulse modulation
• Digital modulation (QPSK, QAM, etc...)
For example, if an RF signal pulse modulated at 50 Hz with a 10% duty cycle is measured with the
averaging factor set to 128, the measured power reading will be 10% of the peak power during pulse ON
periods. Because the signal is modulated at a low pulse rate (below about 1 kHz), the 8650A will
synchronize the readings precisely with the start of a pulse so that each displayed reading is averaged
over a whole number of pulses (that is, there are no fractional pulses included in the measurement).
This eliminates a significant amount of noise from the readings. It is important to remember that even