HP 8648 A/B/C/D - Changpuak.ch

A 13 Pulse Modulator
(HP 8648B/C/D
Option lE6)
Al4 Modulation
Generator
(Option lE2)
A30 Pager Encoder
(HP 8648A Option 1EP)
The pulse modulation module is a thick film circuit mounted inside the
instrument. The main inputs are:
RF output from the A10 frequency extension module
TTL pulse from the rear-panel PULSE IN connector
The module is supplied with -15V, +5V, GND, data and enable lines,
from the A3 motherboard assembly via a twisted wire assembly.
If Option lE2 is present, the power and lines are routed from the
motherboard via the Al4 modulation generator assembly.
The modulation generator contains the DSP (digital signal processor),
memory, DAC, serial I/O for the other assemblies, and output filters. It
generates sine, square, triangle, and saw (or ramp) waveforms used to
modulate the AM, FM, and 4M states of the instrument.
When the instrument is using the variable frequency/waveform
source, the modulation generator will work as an internal modulation
source connected to the MOD INPUT/OUTPUT port. The modulated
signal can be monitored from the MOD INPUT/OUTPUT port as a
2 Vp-p signal.
This assembly has a serial communication port and communicates with
the main controller on the A3 motherboard through this port. The
calibration data for the modulation generator output level is stored in
EEPROM on this assembly.
The modulation generator has its own crystal controlled oscillator.
The DAC output signal is filtered by a 50 kHz cut-off, low-pass filter.
The encoder contains the DSP (digital signal processor), memory, DAC,
serial I/O for the other assemblies, timebase, and output filters.
The pager encoder generates FLEXTM, FLEX-TD, or POCSAG
formatted 2-level or 4-level FSK signals. It also generates
variable-frequency sine, square, triangle, and saw (or ramp)
waveforms. When the instrument is either in the pager encoding
settings state or using the variable frequency/waveform source, the
encoder will work as an internal modulation source connected to the
MOD INPUT/OUTPUT port. The modulated signal can be monitored
from the MOD INPUT/OUTPUT port as a 2 Vp-p signal.
This assembly has a serial communication port and communicates with
the main controller on the A3 motherboard through this port. The
calibration data for the encoder output level is stored in EEPROM on
this assembly.
The memory consists of EEPROM, SRAM, and flash memory. The flash
memory stores the long pager message which will be generated by an
external controller.
To achieve precise timing accuracy for pager protocol, the encoder has
its own timebase unit (TCXO).
The DAC output signal is filtered by either the 10th order Bessel
low-pass filter (-3 dB at 3.9 kHz) or a 50 kHz cut-off, low-pass filter.
Theory of Operation 5a-9