Fluke 8588A Operator's Manual page 55

Reference Multimeter and 8 ½ Digit Multimeter
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RF Power Menu
Push  and then (RF Power) to enable the RF Power function. If a RF
sensor is not connected, a connection message at the bottom of the screen
prompts you to do so. This section explains the RF Power menu. See the screen
below:
iei034.png
When a compatible sensor is plugged into EXT PORT, the top of the RF Power
menu shows the sensor type and serial number. The lower part of the screen has
two parameters that can be changed with the navigation keys and numeric
keypad:
Frequency: Power readings are based on the frequency of the signal to be
measured. After the sensor is plugged in, frequency is set to a default of 50 MHz.
Use the navigation keys or the numeric keypad to change the frequency in that
field. The allowable frequency values are determined by the connected sensor
and generally include 0 Hz.
Reference level: Use the reference level to make relative measurements. The
power-on default is -99 dBm. To change the reference level, use the navigation
keys to highlight and select Reference level. The range of reference level is
99 dBm to -99 dBm. When other units are selected, the reference level range is
shown in Table 13. The reference level can also be set by pushing  (Last
Reading).
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