MDSR
Modulation
Demodulation Software Radio
(SDR)
MDSR
based upon SDR
A radio
communication system where the modulating and
demodulating components that have typically been
implemented in hardware are instead implemented using
software on a personal computer or other embedded
computing devices using by a converter. While the concept
is not new, the rapidly evolving capabilities of digital
electronics are making practical many processes that were
once only theoretically possible!
A basic MDSR(SDR) may consist of a computer (PC) equipped
with a sound card, or other analog-to-digital converter,
preceded by some form of RF front end. Significant
amounts of signal processing are handed over to the
general purpose processor, rather than done using
special-purpose hardware. Such a design produces a radio
that can receive and transmit a different form of radio
protocol (sometimes referred to as a waveform) just by
running different software and any soundcard!
The MDSR software performs all of the demodulation,
filtering (both radio frequency and audio frequency),
signal enhancement (equalization and binaural
presentation). Uses include every common amateur
modulation: morse code, single sideband modulation,
frequency modulation, amplitude modulation, and a variety
of digital modes such as radioteletype, slow-scan
television, and packet radio. Amateurs also experiment
with new modulation methods: for instance, the DREAM
open-source project decodes the COFDM technique used by
Digital Radio Mondiale and compatible stations.
demodulator
mf 455 khz
The
ideal receiver scheme would be to attach an
analog-to-digital converter to an antenna. A digital
signal processor would read the converter, and then its
software would transform the stream of data from the
converter to any other form the application requires.
An ideal transmitter would be similar. A digital signal
processor would generate a stream of numbers. These would
be sent to a digital-to-analog converter connected to a
radio antenna.
The ideal scheme is, due to the actual technology
progress limits, not completely realizable, however.
Most receivers utilize a variable frequency oscillator,
mixer, and filter to tune the desired signal to a common
intermediate frequency or baseband, where it is then
sampled by the analog-to-digital converter. However, in
some applications it is not necessary to tune the signal
to an intermediate frequency and the radio frequency
signal is directly sampled by the analog-to-digital
converter (after amplification).
Real analog-to-digital converters lack the discrimination
to pick up sub-microvolt, nanowatt radio signals.
Therefore a low-noise amplifier must precede the
conversion step and this device introduces its own
problems. For example if spurious signals are present
(which is typical), these compete with the desired
signals within the amplifier's dynamic range. They may
introduce distortion in the desired signals, or may block
them completely. The standard solution is to put
band-pass filters between the antenna and the amplifier,
but these reduce the radio's flexibility - which some see
as the whole point of a software defined radio. Real
software radios often have two or three analog
"channels" that are switched in and out. These
contain matched filters, amplifiers and sometimes a
mixer. soundcard, interface
About
the Author of DADP and BiLIF projects Alex
Schwarz (VE7DXW) is an advanced HAM and a graduate of the
HTL, Innsbruck. He moved to Vancouver (Canada) in 1990 and
has since been involved in professional communication systems
(LDR trunking) and digital point to point wireless network
systems. In 2005 he started work in the Biomedical
Engineering Department at C&W Hospital in Vancouver.
This
website is designed to use with frame-based compatible
browsers!
These
are the links:
software.htm
downloads.htm
about.htm,
DADP.htm
DRM_455kHz_to_LF_Converter.htm
bilif.htm
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