Manual - 8500A Series Peak Power Meter - Giga-tronics

Operation
2.10.5 Power Ratio Measurements
To make ratio measurements, the power measured by both channels must be within the specified power
measurement range of the PPM system. When operating in CW, this power range is -40 to +20 dBm. In
the Peak Mode, this power range is -20 to +20 dBm. Power readings taken in the Ratio Mode outside of
these ranges will result in an error display.
The Ratio Mode only provides the ratio of A/B, not vice versa. The PPM can ratio two CW signals, two
Peak signals, or a combination of both. The following procedures show how to perform each of these
ratio’ing operations.
Ratio’ing Two CW Signals
This is the easiest ratio function of the PPM. Proceed as follows:
1. Allow the PPM to warm up for at least 30 minutes. Then Self-Calibrate both channels. From
power-on, press [CW] [MENU] (1) [F3] [F1].
Follow the displayed prompts to complete the Self-Cal. After Self-Cal has completed, the PPM
will be measuring CW power in channel A.
2. Select the Ratio Display Mode by pressing [MENU] (7) [F2].
3. The default mode for power ratio measurements is for Peak power on both channels. To set both
channels for CW operation, press [A] [F2] [B] [F2].
The PPM will now be reading the ratio of A/B. Normally this is expressed in dB, however, it can also be
expressed as a linear reading (such as 19654 EXP=-4) by pressing [dB/mW]. The display indicates that
two CW signals are being ratio’ed by displaying CW/CW in the lower right hand corner of the display.
Remember that the frequency of operation or Cal Factor must be entered using the FREQ key, and any
desired Offsets should also be included. These two functions are described in Sections 2.8.3 and 2.8.4.
Ratio’ing Two Peak Signals
The point in time at which readings of Peak power are taken in both channels for ratio’ing purposes is
determined by the setting of the Cursor Delay. Although it is most desirable that both pulses being
monitored occur at exactly the same time, in practice this would be a very rare event. Therefore, the
signals to be measured must be carefully evaluated to ensure that accurate readings are taken.
The Cursor Delay must be set so that samples are being taken on both the channel A and B pulses. See
Figures 2-12 and 2-13 for an examples of good and bad Cursor Delay settings in this situation.
The following are guidelines that can be used when ratio’ing two Peak signals:
1. Make a single channel Peak measurement using the Graph Mode (Autoscaling is recommended).
2. Set the Cursor Delay so that the power reading (CSR PWR) is being taken close to the center of
the pulse (see Figure 2-12).
Figure 2-12. Typical Peak Power Ratio Display
Manual No. 20790, Rev C, November 1998 2-35
Superceded by Revision D, March 2009