to MDSR website:
"Modulator-Demodulator Software Radio"
and other related projects!
based upon SDR
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!
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
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.
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 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.
the Author of DADP and Bi-LIF projects
(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. He can be reached
through his email address: [email protected]
and URL info
Alex, VE7DXW: mail
Please feel free to
join our MDSR support and discussion forum at:
The official URL of
Please join the
Scistarter RF-Seismograph group "Sience we
can do together": SciStarter
About Alex VE7DXW and MDSR @
Please donate to the
MDSR user group. So far all the work to create the
LIF converter, the DADP software and the DADP-SA was
done by volunteers. Our aim is to provide a cost
effective alternative to expensive commercial SDR
radios. The website is designed and hosted by Guy
Roels (ON6MU) and the application programming is also
done by Guy. All the hardware was paid for by Alex
Schwarz (VE7DXW) and he has spent countless hours
writing the DADP audio processor software. The whole
project runs on a shoestring budget. Your donation
shows that there is support for this kind of
development and it enables us to continue our
research and development of the MDSR concept into a
product that all amateur operators can use.
Many thanks in advance!
Order the kit online
Everybody is welcome to join our MDSR Forum & group. The software and the
documentation are available to everybody at no charge
as long as the use is for noncommercial amateur radio
if you want to commercialise, publish or distribute
this or other projects found on this website
then you need to ask permission to do so.
Any modification will be done at your own risk!