Keysight FieldFox Handheld Analyzers Service Guide 69
Theory of Operation
Measurement Group
Time Base
The Time Base is an internal TCXO that produces 90 MHz signals for use
throughout the analyzer.
A 10 MHz signal at the Ref In/Trig input may be used to provide an external
time base. The external time base function is controlled via the user interface.
Refer to the “Frequency Reference Source” section of the FieldFox Analyzer
User’s Guide (Part Number N9927-90001) for additional information.
The internal 10 MHz frequency reference is available from the Ref/Trig Out
connector on the right-side panel. Use this signal as a common frequency
reference when making measurements using external equipment
Filters, MUX, and ADC’s
The three Filters filter the IF signals in preparation for the ADC. Filter
characteristics are fixed (not programmable).
The ADC’s digitize each of the IF signals received from the A4 RF board. The
input to one of the ADC’s is multiplexed between the NA-A and NA-B input
signals.
The 14-bit ADCs sample at a rate of 30 mega samples per second.
Each ADC may be put into a low power mode when not active.
Temperature Sensors
The SB1 Temp Sensor is located on the A4 RF board side of the A5 System
board near the headphone jack (J3).
The SB2 Temp Sensor is on the A4 RF board side of the A5 System board near
the edge of the board against the battery compartment. This temperature
sensor is not under a shield.
Audio Output
The speaker is located on the left side panel of the case. Left and right audio
signals from the A6 SOM board go to the headphone jack on the A5 System
board. These signals are then combined to create a single mono signal for the
speaker. An amplifier drives the speaker. Plugging in the headphones disables
the speaker output.
LAN Connector
The LAN connector supports the LAN interface on the A6 SOM board. See
“LAN Interface” on page 87 for more details.
SOM Connector
Refer to “A6 SOM Board” on page 70 for information on SOM (System on
Module) functions.
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