LDI Intellectual Property.
Not for secondary distribution or replication, in part or entirety.
DIGISONDE-4D
SYSTEM MANUAL
VERSION 1.2.11
SECTION 1 - GENERAL SYSTEM DESCRIPTION 1-7
1:7. The new 16-bit analog-to-digital converters (ADCs) and the digital receivers provide increased preci-
sion for amplitude and phase measurements and reduced temperature sensitivity. Since the Digisonde-4D must
operate over a large frequency band of more than eight octaves (from 0.1 MHz to 30 MHz), it is important to
protect the ADCs from saturation by strong interferers operating in this large band. Saturation of the ADC
would destroy the narrowband filtering of the digital receiver. An analog tracking filter in combination with
automatic digitally controlled amplifier gain at the receiver input limit the ADC input voltages to specified val-
ue.
1:8. The physical dimensions of the Digisonde-4D remain unchanged since the Digisonde
®
Portable Sound-
er was introduced in 1990, consisting of two 19” chassis, one housing the two-channel transmitter power ampli-
fiers and half-octave filters, the other the signal synthesizers, receivers, and digital signal processors. The sys-
tem compensates for a low power transmitter (300 W vs. 10 kW for original Digisonde-128 and 256 models) by
employing intrapulse complementary phase coding with digital pulse compression, Doppler integration, and the
patented Radio Frequency Interference Mitigation algorithm RFIM which enhances the processing gain by 35
dB.
1:9. The Main (upper) Chassis (see Figure 1-5) contains the following functional assemblies:
a. Cardcage with Digisonde-4D electronics
b. Digital transmitter / timing card
c. Digital receiver card
d. Four analog tracking filter cards (“tuners”)
e. Pre-processor card
f. Built-in test (BIT) card
g. Backplane with 61.44 MHz Master Frequency Standard
h. Two embedded computer platforms (Control Platform and Data Platform)
i. DVD R/W mass storage drive
j. Removable Hard Disk tray
k. Power distribution board with DC/DC converters
l. Antenna switch
m. Three axial fans
1:10. The Power Amplifier Chassis (lower) Figure 1-6 contains the following assemblies:
a. Two 150 W peak power solid state amplifiers
b. Two half-octave filter boards for harmonic suppression
c. Input power relay
d. Two axial fans
1:11. The outer moulded case, and its removable front and rear covers, protect the main and power chassis
during operation, transit and storage. As well as containing chassis mounting hardware and miscellaneous fit-
tings, the case houses a 28 VDC power supply unit, two high volume axial fans, a power and signal distribution
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