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DIGISONDE-4D
SYSTEM MANUAL
VERSION 1.2.11
SECTION 1 - GENERAL SYSTEM DESCRIPTION 1-45
c. The cost of purchasing or developing such technology.
d. The risk involved in depending on certain technologies, especially if some of the technology needs
to be developed.
e. The capabilities of the intended user of the system, and its expected willingness to learn to use and
maintain it; i.e., how complicated can the operation be before the user will give up and not try to
learn it.
1:99. The question of what technology can be brought to bear on the realization of a new ionospheric sound-
er was answered in a survey of existing technology in 1989, when the DPS portable sounder development start-
ed in earnest. This survey showed the following available components, which showed promise in creating a
smaller, less costly, more powerful instrument. Many of these components were not available when the previ-
ous generation of Digisonde
®
(circa 1980) was being developed:
• Solid-state 300 W MOSFET RF power transistors
• High-speed high precision (12, 14 and 16 bit) analog to digital (A–D) converters
• High-speed high precision (12, 14 and 16 bit) digital to analog (D–A) converters
• Single chip Direct Digital Synthesizers (DDS)
• Wideband (up to 200 MHz) solid state op amps for linear feedback amplifiers
• Wideband (4 octaves, 2–32 MHz) 90
o
phase shifters
• Proven Digisonde-256 measurement techniques
• Fast, single board, microcomputer systems and supporting programming languages
1:100. Many of these components are inexpensive and well developed because they feed a mass market indus-
try. The MOSFET transistors are used in Nuclear Magnetic Resonance medical imaging systems to provide the
RF power to excite the resonances. The high speed D–A converters are used in high resolution graphic video
display systems such as those used for high performance workstations. The DDS chips are used in cellular tel-
ephone technology, in which the chip manufacturer, Qualcomm, is an industry leader. The DSP chips are wide-
ly used in speech processing, voice recognition, image processing (including medical instrumentation). And of
course, fast microcomputer boards are used by many small systems integrators which end up in a huge array of
end user applications ranging from cash registers to scientific computing to industrial process controllers.
1:101. The performance parameters were well known at the beginning of the DPS development, since several
models of ionospheric pulse sounders had preceded it. The frequency range of 1 to 20 MHz for vertical sound-
ing was an accepted standard, and 2 to 30 MHz was accepted as a reasonable range for oblique incidence meas-
urements. It was well known that radio waves of greater than 30 MHz often do propagate via skywave paths;
however, most systems relying on skywave propagation don’t support these frequencies, so interest in this fre-
quency band would only be limited to scientific investigations. A required power level in the 5 to 10 kW range
for pulse transmitters had provided good results in the past. The measurement objectives were to simultaneous-
ly measure all seven observable parameters outlined at Paragraph 1:26 above in order to characterize the fol-
lowing physical features:
• The height profile of electron density vs. altitude
• Position and spatial extent of irregularity structures, gradients and waves
• Motion vectors of structures and waves
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