14-7
Block Diagram Theory of Operation
Block Diagram 1
The primary measurements of the A9 Global Test and Demod assembly are phase,
frequency, and amplitude information of the 0.3 GMSK modulation signals. The A9
Global Test and Demod assembly measures these by digitizing the 700 kHz IF signal and
usinghigh speed DSP hardware and algorithms. The DSP hardware must be “armed” and
then “triggered” to synchronize with the incoming modulation signal. These various
trigger signals are shown on Block Diagram 1 and the operation of these is described in
the HP/Agilent 8922 Users Guide.
The results of these measurements are displayed using the DSP ANL screen on the HP/
Agilent8922. The digital data information is also used by the HP/Agilent 8922E/F/G/H to
setupand maintain a call with a GSM mobile phone. This is done in “real time” as the HP/
Agilent8922E/F/G/H and mobile phone simultaneously send and receive from each other.
A18 Spectrum Aanalyzer
The A18 Spectrum Analyzer assembly receives the 114.3 MHz signal from the A16
Receiver assembly. The analyzer can only view frequency spans up to 4 MHz due to the
bandwidth of this input signal. A phase lock loop inside the spectrum analyzer is used to
downconvert the 114.3 MHz signal which is then amplified, filtered, and detected. The
synchronization signal for the display is controlled by the A19 Measurement assembly.
This causes the PLL signal to sweep across the frequency span selected. In addition to
normal spectrum analysis, the HP 8922 spectrum analyzer is used to help measure the
amplitude profile of the pulsed GSM signal. The upper 30 dB of the pulse envelope is
accurately determined by the A9 Global Test and Demod assembly, however, the lower
levelportions of the pulse amplitude is measured with the wide dynamic range of the A18
Spectrum Analyzer assembly.
Thisinternal spectrum analyzer is a useful tool to view the incoming RF signal and verify
that the A23 Input and A11 Receiver Mixer assemblies are working correctly. The A18
Spectrum Analyzer assembly contains diagnostic test points to verify gain, attenuation,
and bandwidth controls. Because of the wide dynamic range of the A18 Spectrum
Analyzer assembly it is used by the diagnostics to measure pulse on/off ratio of the A12
Pulse Attenuator assembly.
A2 Audio Analyzer 2 A3 Audio Analyzer 1
These modules are leveraged from an earlier product, the HP/Agilent 8920A, which is
primarily an analog communications test set. Many of the audio circuits in these
assembliesare not used by the HP/Agilent 8922 and will not be covered in this discussion.
Refer to the HP/Agilent 8920A Assembly Level Repair manual if further detail on these
modules is required.
For the HP/Agilent 8922, the primary function of these assemblies is to provide the
oscilloscope functions. The HP/Agilent 8922 contains no specialized oscilloscope
module, only these two analyzer assemblies and the A19 Measurement assembly. These