Robotron Pty Ltd G9P 用户手册
WiNRADiO G39DDC User’s Guide
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The preceding spectrum display is that of the WiNRADiO G313 receiver, a
typical representative of this type of SDR receivers, belonging to a class of
receivers also referred to as SDR Tier Two or Software-Reconfigurable
Radio. In SDR Tier Two radios, software is used to control and redefine a
variety of modulation techniques, spectrum bandwidth, and other essential
parameters and functionality of a radio receiver.
DDC-Based Receivers – The Excelsior
The arrival of the digital down-converter (DDC) has moved the hardware-
software dividing line of SDR Tier Two category receivers closer to the
antenna, and introduced additional benefits.
Advances in digital electronics, especially the introduction of fast ADCs and
field-programmable gate arrays (FPGA) made it possible to eliminate some, if
not all, hardware-based heterodyne processes and introduce the concept of
digital down-conversion, where the local oscillator and a mixer can be replaced
with a single software-reconfigurable hardware component.
Modern ADCs can achieve a sampling rate of 100 MHz and beyond. The
Nyquist theorem says that the maximum frequency that can be sampled
needs to be smaller than half of the sampling rate (see
www.wikipedia.org/wiki/Nyquist_frequency). So, we have the potential to
sample almost 50 MHz of spectrum at once.
However, one ADC does not yet make an SDR, and more software processes
are involved. Because of the very high amount of data, and issues related to
analog down-conversions that (still) need to take place to be able to achieve a
receiving frequency range in the order of GHz, it is necessary to reduce the
instantaneous spectrum bandwidth to a more manageable value.
In the Excelsior, we have chosen this to be 16 MHz as a very good
compromise – still much wider than that of most contemporary receivers.
Nyquist theorem says that the maximum frequency that can be sampled
needs to be smaller than half of the sampling rate (see
www.wikipedia.org/wiki/Nyquist_frequency). So, we have the potential to
sample almost 50 MHz of spectrum at once.
However, one ADC does not yet make an SDR, and more software processes
are involved. Because of the very high amount of data, and issues related to
analog down-conversions that (still) need to take place to be able to achieve a
receiving frequency range in the order of GHz, it is necessary to reduce the
instantaneous spectrum bandwidth to a more manageable value.
In the Excelsior, we have chosen this to be 16 MHz as a very good
compromise – still much wider than that of most contemporary receivers.