14-9
Block Diagram Theory of Operation
Block Diagram 2
Block Diagram 2
RF Generator
AF Generator
A15 Reference
TheA15 Reference assembly contains the circuits necessary to generate reference signals
for the other assemblies in the HP/Agilent 8922. The A15 Reference assembly can be
locked to an external signal of 1, 2, 5, 10 or 13 MHz or can operate without an external
reference by using its own 10 MHz TCXO.
Anoptional high stability oscillator (Option 001) is available for the HP/Agilent 8922 that
provides a more accurate and stable reference. The output from this oscillator is routed to
therear panel, where it must be connected to the Reference Input for the HP/Agilent 8922
tolock onto this signal. The frequency of the (optional) high stability timebase is adjusted
with a screwdriver while the (standard) internal Temperature-Compensated Crystal
Oscillator (TCXO) is adjusted by setting internal DAC values. Both of these adjustments
are thoroughly explained in chapter 7, Adjustments and Calibration.
If the A15 Reference assembly is replaced, an error message “Frequency Reference
Calibration Lost” will be seen during instrument power-up. It is necessary to perform the
adjustment for the internal TCXO to remove the error message and restore calibrated
operation.
A special feature of the A15 Reference assembly is the ability to offset all reference
signals in the HP/Agilent 8922. The amount of offset can be set by the user by changing
the A15 Reference assembly DAC value. The primary screen to control operation of the
A15 Reference assembly is the Configure Screen; refer to the Users Guide for a more
complete discussion on the operation of the Reference section.
Diagnosticprocedures for the A15 Reference assembly check lock detectors to make sure
that the internal loops are locked, and level detectors to check if RF power is available on
keyreference signals. The diagnostics cannot check the frequency accuracy of the internal
oscillators.

A5 Premod Filter and NSM

The A5 Premod Filter and NSM assembly contains the necessary circuits to convert the
user’s digital input data and clock signals into a GMSK waveform. The inputs to the
module are a very accurate 270.833 kHz clock signal and digital TTL level data. On the
HP/Agilent 8922A these two signals are provided directly by the user at the front panel;
on the other HP/Agilent 8922’s, these signals are generated by other assemblies.