Front Panel Operation
Publication 31470-001, Rev C, November 2, 2017
2-31
2.4.8
Measurement Collection Modes
Using a wide range of CW and Modulation Power Sensors and the GPIB fast measurement collection modes, the
Series 8650B meters provide typical reading speeds of 1750 readings per second in the GPIB Swift Freerun
mode, 800 readings per second in the GPIB Fast Modulated mode, and 26,000 readings per second in the GPIB
Fast Buffered mode.
Three GPIB Swift mode triggering controls are available: Freerun, Bus triggered, and TTL triggered modes. Bus
and TTL allow triggering control of individual measurement points. When using BUS or TTL triggering, data can
be stored in an internal data buffer. When using Freerun continuous triggering, data can be read immediately.
GPIB Fast Buffered mode power readings are internally buffered for readout at the completion of the GPIB Fast
Buffered measurement interval. Maximum measurement rate is about 26,000 readings per second. Data
conversion and GPIB communication time are not included in this figure. The maximum buffer size is 5000
readings, or about 193 ms of data collection at the maximum reading rate.
2.4.8.1
CW Mode
This mode is for measuring an unmodulated Continuous Wave (CW) signal. In this mode the RF signal level must
be constant for accurate readings to be made. If the signal level changes, a settling time for the internal digital
filter is required in order for measurements to be made to the specified accuracy.
The settling time (the time required for a measurement based on an averaging of samples to adapt to a changed
condition and become accurate again) is affected by various factors. The maximum settling time is equal to 20
ms multiplied by the averaging factor (for example, if the averaging factor is 128, the maximum settling time is
2.56 seconds). In most situations the actual settling time is well below the maximum.
2.4.8.2
PEAK Mode (80350A Peak Power Sensor)
The Peak mode is for instantaneous peak measurements of the RF power level of a pulse modulated signal
during pulse ON periods. The measurement is based on an instantaneous sample taken at a particular point in
time. Sampling is triggered by a pulse rising edge either in the modulated signal itself or in a supplied trigger
input signal, followed by a programmable delay. The trigger/delay combination makes it possible to specify
exactly what part of the pulse is sampled.
In the peak mode, each displayed reading can consist of a single sample or of an average of multiple samples,
each taken at the exact same time relative to the pulse’s rising edge. If the averaging factor is set to 1, single
samples are used. If it is other than 1, the averaging factor will determine the filter settling time over which the
multiple samples will be taken and averaged.
Because the peak mode measures the RF power instantaneously (at the top of the pulse, provided that the delay
has been set correctly), no assumptions are made about the pulse shape or duty cycle. In fact, it is possible to
profile the pulse by sweeping the delay time over a range of values to reveal the pulse shape from start to finish.
NOTE:
In the peak mode the 8650B does not know where the peak is. It samples the pulse where it is told
to sample the pulse whether or not the point sampled is really the peak point. This mode is therefore less
intelligent than the BAP mode and must be used carefully, but its flexibility makes it a powerful tool for
studying modulated signals.
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