Software Defined Radio SDR for Amateur Radio * an overview

Report
Steve Dick, K1RF
May 9, 2012
As defined in Wikipedia:
 A software-defined radio system, or SDR, is a
radio communication system where components
that have been typically implemented in
hardware (e.g. mixers, filters, amplifiers,
modulators/demodulators, detectors, etc.) are
instead implemented by means of software on a
personal computer or embedded computing
devices.
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A basic SDR system may consist of a personal computer 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 being done
in special-purpose hardware. Such a design produces a radio which
can receive and transmit widely different radio protocols (sometimes
referred to as waveforms) based solely on the software used.
 In the long term, software-defined radios are expected to become the
dominant technology in radio communications.

Antenna
I,Q
R.F.
Front End
I,Q
High Quality
Sound Card
P.C., Laptop,
Netbook, or
Embedded
processor
Example architecture
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Modern conventional Radios are usually controllable via a computer with
CAT or similar interfaces. These are Software Controlled radios, not
software defined radios.
Modern conventional radios may use Digital Signal Processing for
enhanced filtering for better performance than conventional filters and to
eliminate multiple downconversions. These are NOT software defined
radios.
Conventional radios having single sideband capability can feed audio
to/from a PC for what is known as digital modes. This is real audio, not
complex baseband I,Q. However, the digital mode modulation and
demodulation can be considered software defined radio (modulation,
demodulation, and detection functions)
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Does not look or feel like a real conventional radio. Uses a computer-based
graphical user interface. No knobs!!!
Needs some getting used to after many years using a conventional radio.
Getting the software set up and working properly can be a challenge. It is
definitely not plug and play and requires integrating multiple software
packages
There are processing time lags on the P.C. (on the order of milliseconds).
This is generally not a problem except when using Morse Code (CW). You
can’t listen to your own signal and try to send Morse Code. Your brain gets
confused from the time lag. A separate tone source with zero lag solves
this problem
You can’t receive signals at the center of the spectrum. This is D.C. and
soundcards don’t go down to D.C. Also, a lot of noise is picked up in this
part of the spectrum (60 cycle hum, noise due to ground loops, etc) so you
tune on either side of the spectrum center.
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Sampling basics
In 1933, Harry Nyquist discovered
that to accurately recover all the
components
of a periodic waveform, it is
necessary to sample a signal at twice
the maximum bandwidth of the
signal being measured. That
minimum sampling frequency is
called the Nyquist criterion. This may
be expressed as: fs = 2 bw
where fs is the sampling rate and bw
is the bandwidth.
See the math isn’t so
bad, is it?
Courtesy Pentek - Software Defined Radio Handbook
In real life, a good rule of thumb is to
use the 80% relationship:
Bandwidth = 0.8 x ƒs/2 to allow for
readily achievable filtering instead of
“brick wall” filtering
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
The mixer is basically a
multiplier (analog or digital) in
which the local oscillator is
multiplied by the incoming
signal. For sine waves, the
output signals are sum and
difference frequencies of the
local oscillator and the
incoming signal frequencies.

One of the two signals is kept
by filtering. The other signal
is rejected by filtering. Any
residual is known as an
“image” and is undesireable
Local oscillator = 14.000 MHz
Incoming carrier = 14.001 MHz
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Q = Quality factor
Q = F0/Delta F where
 F = center frequency
 Delta F = bandwidth
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Higher Q = narrower
bandwidth or high
selectivity
Lower Q = wider
bandwidth or low
selectivity
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
The conventional heterodyne radio receiver (A.K.A.
Supersonic Heterodyne or Superheterodyne) shown
has been in use for nearly a century. Let’s review the
structure of the analog receiver so comparison to a
digital receiver becomes apparent.

First the RF signal from the antenna is amplified,
typically with a tuned RF stage that amplifies a region of
the frequency band of interest.

This amplified RF signal is then fed into a mixer stage.
The other input to the mixer comes from the local
oscillator whose frequency is determined by the tuning
control of the radio. The mixer translates the desired
input signal to the IF (Intermediate Frequency) .

The IF stage is a bandpass amplifier that only lets one
signal or radio station through. Common center
frequencies for IF stages are 455 kHz and 10.7 MHz for
commercial AM and FM broadcasts.

The demodulator recovers the original modulating
signal from the IF output using one of several different
schemes. For example, AM uses an envelope detector
and FM uses a frequency discriminator.

In a typical home radio, the demodulated output is fed
to an audio power amplifier which drives a speaker.
I.F. frequency Trades off
Image rejection
vs. selectivity
This diagram shows a single
conversion (local oscillator plus
mixer, IF Amp). Multiple
conversions provide increased
selectivity. So does DSP filtering
used in modern designs.
Courtesy Pentek Software Defined Radio Handbook
Classic
Addison 5
AM table radio
Circa 1940
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I,Q
PC or
Embedded
processor
Performs
decimation
A/D at front
end at R.F.
Then all
digital
conversion
to baseband
– but costly
Courtesy Pentek Software Defined Radio Handbook
The “High Priced Spread” – Direct Digital Conversion

Analog
Downconverter
Analog
RF Signal
RF
Tuner
Digital Local
Oscillator
(DDS or SI570)
Tayloe
Detector
Dual
flip-flop
Divide by 4
I,Q
Sound
Card
Analog
Baseband
Samples
I,Q
P.C.
Or laptop
Digital
Baseband
Samples
The “Low Priced Spread” – soundcard-based
A/D at back
end with
A/D
conversion
done with
sound card.
– low cost
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Typical value
122.88 MHz
Sample rate
Typical value
96 KHz
baseband
Sample rate
(Sound card)

The “tuning knob” sets the digital local
oscillator to the center of the
baseband spectrum in the area of
interest

The “Bandwidth” control sets the
bandwidth of the low pass filter using
different amounts of decimation.
Wider bandwidths result in higher final
output sample rates; narrower
bandwidths result in lower final output
sample rates. Low pass filter can
typically be adjusted from megahertz
to kilohertz
Courtesy Pentek Software Defined Radio Handbook
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Antenna
Baseband I,Q
R.F.
Front End
A/D Converter
(sound card)
and processing
(PC)
• Band limited by
RF front end.
• Typically limited
to the KHz to
10s of KHz range
Negative
Frequencies
Zero frequency
Positive
frequencies
Bandwidth approaches +/- 48KHz with good soundcards
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A Software Defined Radio for the Masses Part 1
A Software Defined Radio for the Masses Part 2
A Software Defined Radio for the Masses Part 3
A Software Defined Radio for the Masses Part 4
Written by Gerald Youngblood, K5SDR, now
CEO and President of FlexRadio Systems. In
April of 2003 he founded FlexRadio Systems
to market the first Software Defined Radio
products to the Amateur Radio market
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Fists of Fourier
Courtesy garage-shoppe.com
Give me an
I, give me a
Q, and I can
demodulate
anything!!!
Courtesy SDR for the masses, Part 1
The Fast Fourier Transform (FFT) does all the heavy lifting in SDR software
to implement high performance filters in place of expensive hardware filters
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Rear view
Flex 5000A “The Cadillac of SDR”
www.flexradio.com
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integrates all I/Q data and hardware
control over a single FireWire ® (IEEE1394a) connection to a user provided
computer.
Top Performing Narrow-Spaced TwoTone 3 rd Order IMD Dynamic Range
of ~100 dB on 14 MHz Using a 2 KHz
Spacing
Narrow Spaced 3 rd Order Intercept
Point: Greater Than 39 dBm at 2 KHz
Tone Spacing.
Integrated ultra high quality 192 KHz
24-bit ADC and DACs
Full Duplex Operation for
Simultaneous Transmit and Receive
High Stability TCXO
100 watts PEP on 160 to 6 meters
Cost $2799
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Built by K1RF
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PCB ~ 8” X 8”
Genesis Radio G11
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Up to 5 band transceiver
10 watts out minimum on all bands
QSD and QSE-based architecture
Semi-kit. All Surface mount
components preassembled
IP3 30-32dBm
MDS is -116 to -122dBm. RF
preamplifier on: MDS is from -130 to 133dBm.
Image rejection: -35 to -60 dB
[hardware], better than 60dB
[software]
RX sensitivity: 0.15-0.2uV for 10 dB
S/N ratio. Max S/N measured: 70dB.
SFDR (Spurious free dynamic range)
is 93-100dB these results are with
signals spaced 5 kHz or more.
Built-in extras incl. CW keyer
Cost $299 less heatsink. You provide
your own chassis,soundcard,PC
www.genesisradio.com.au
http://groups.yahoo.com/group/GenesisRadio/
Sample youtube video (SSB reception)
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UHFSDR
WB6DHW.com
UHF SDR Yahoo Group
Parts cost - ~$200.00
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Full duplex transceiver
Architecture based on
Front end high speed
ADC and FPGA based
DDC and DUC
Built-in audio codec
Very high performance
~ ½ watt output
Connects to PC via
Ethernet
Approximate cost will be
~900.00
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Several companies or amateur radio groups have developed selfcontained SDR transceivers that don’t use PCs.
 They are based on very low cost DSP microcomputers that have
significant digital signal processing capabilities, used in conjunction
with low cost audio CODECs and a low cost programmable oscillator.

Example: Microchip dsPIC33FJ128MC804 “Digital Signal Controller”.
Cost ~$6 qty 1. 40MIPS, I2C, ADC and DAC, PIO
 Low cost helper chips:
 TI audio codec TLV320AIC3204IRHB
 Silicon Labs Si570 10 Mhz TO 1.4 Ghz I2C Programmable
XO/VCXO
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There is also the first ever standalone digital modem,
the NUE-PSK, a digital modem for PSK31 and RTTY field use ...
without a PC!
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NUE-PSK
Digital Modem
SDR Cube Transceiver
www.nue-psk.com
Featured in
QEX Mar-Apr 2008
Base price $220
SDR2GO
kit ~$70.00
Austin QRP club
See Austin Summerfest 2010
www.sdr-cube.com
Overview slides
Complete kit $424
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KX3 Self-contained operation
Audio out to soundcard/PC
• 160-6 meters, SSB/CQ/DATA/AM/FM modes
For use with 3rd party
• 10W PEP (100W with KXPA 100 amp)
software for SDR apps and
digital modes
• Only 1.5 pounds (0.7Kg)
• Current drain as low as 150 mA on receive
• Ultra compact portable/mobile/home
• Internal 8 - AA battery holder
• Receiver performance rivals the best conventional transceivers
•Base price $899 kit, $999 assembled
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Invented by Dan Tayloe, Patent no. 6,230,000, May 2001.
It has four unique properties:
▪ Less than 1 db of conversion loss!!!
▪ “Free” tracking bandpass selectivity (Q = 3,500 at 7 MHz), with a user
definable bandwidth
▪ Very high dynamic range - A high 3rd order intercept (+30 dbm).
▪ An extremely compact and simple design using low cost components
compared to other zero IF I-Q quadrature detectors

Conventional passive mixers generate sum
and difference frequencies. Therefore, the
conversion loss using an ideal mixer is at least
3 db, with a typical conversion loss of 4-6 db
in practice

The Taylor detector produces only
a difference frequency!!!

Basic design useful into the GHz range

A.K.A. Quadrature sampling Detector (QSD)
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The human ear has about 130 dB of dynamic range. Sound cards strive to have
undetectable distortion to the human ear for hi-fi applications
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The standard for today’s audio reproduction and studio audio
processing is 24 bits at 96 kbits/sec sampling rate, or even 192
kbits/sec sampling rate.
24 bit soundcards come in many flavors and qualities, few if any
approaching the theoretical maximum dynamic range of human
hearing
Soundcard maximum theoretical dynamic range: 6.02 dB x 24 bits 3 dB = 141.48 dB. Lets shave 20 dB off this number for worst case
realism: 121 dB dynamic range. This dynamic range has
undetectable distortion at normal listening levels. When applied to
SDR applications, This is still an impressive dynamic range and
approaches the dynamic range of the best military radios if the RF
front end had perfect linearity and steps are taken to avoid noise
contributing ground loops.
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Take your pick – everyone has their favorites
Can be mounted in PC or used via USB (Preferred for
portability between different PCs or laptops)
Representative list with some user comments:
 Emu 0202, works well but can be a bit touchy to set up correctly.
 M- audio 2496 , works well easy set up.
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Essence stx pic- e, excellent and easy set up.
M-audio delta44, poor, pain in the *** to set set up
Sdr widget, works well. (kit)
Ederol FA66
Sound Blaster X-FI surround 5.1 pro (good performance at low
cost - ~ 49.00)
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USB power
Dual flip-flop
Divide by 4
XTAL oscillator/buffer
Bandpass filter
Tayloe Detector:
CMOS analog switch,
Capacitors,
Dual low noise op-amp
This is the entire schematic for a very high performance single band
RF Front end – Incredible!!! Representative of Tayloe detector
(Quadrature Sampling Detector) - based RF front ends
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http://www.kb9yig.com/
To order
Join yahoo group:
http://groups.yahoo.com/gr
oup/softrock40/
To check on availability
(they go fast!!)
See http://www.qrz.lt/ly1gp/SDR/
For a similar low cost SDR sampler
TinySDR for 80M band
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Latest SDRs are moving to client-server architectures
Get on the internet and use someone else’s Antennas
and RF baseband converter!!
Antenna
I,Q
R.F.
Front End
I,Q
High Quality
Sound Card
P.C. based server
(Linux)
P.C. based client
(Linux or
windows)
Yay! It works!
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
Internet-based: No software required!!: www.websdr.org
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More sophisticated but requires software download; Go to the following
link for description:
http://napan.ca/ghpsdr3/index.php/QtRadio_on_Windows
Download a zipped executable at:
http://napan.com/ve9gj/qtradio-master.zip
Load to a new folder and extract contents
Run QTRdio.exe. Allow access if windows firewall blocks or only
provides limited access
Click on Receiver /Configure and select audio card
Click on Receiver/Quick server list, highlight a server and connect (try
different ones, some are more capable than other, some may not be
operating)
You can now control the other person’s radio over the internet!!
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There is also an Android Client for SDR servers!!
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You can select band, tune it with your mouse scroll wheel, select operating
mode, look at received signal strength on S-meter, set control parameters, etc
Pretty cool to let you try SDR with just a PC and internet connection
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PSK31, PSK63, SSTV, HD SSTV, RTTY,
MFSK16, MFSK32, MT63, Hellschreiber,
Olivia, Packet, PACTOR , Throb,
Contestia, JT6M, Ham DRM, Domino,
DominoEX, DominoF, WSPR, ROS,
SITOR, SITOR-A, SITOR-B, Swedish
ARQ, Clover, CHIP, ALE, PAX, PAX-2,
STANAG, HFDL, NAVTEX, SYNOP,
COQUELET, AOR, WinDRM….
Between amateur and commercial services, there are tens of modes, perhaps
approaching 100!!!
Courtesy George Heron, N2APB
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SDR software can feed other third party software using other
internal software interconnects for IQ audio transfer and
receiver/transmitter control.
Virtual audio cable
Baseband I,Q
Baseband I,Q
SDR software
package
Rocky, PowerSDR IQ, etc.
Virtual Com Port
(Control)
Third Party
software
package
(modulation,
Demodulation,
Control)
Ham Radio Deluxe, FLDIGI, Digipan, etc.
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Software:
- FLDIGI, …
SSB transceiver
A (good) Sound Card
(An external USB sound card is most flexible)
A (fast) PC
Once you’ve wired your station for
one HF mode, you can work
another by just selecting a different
mode in the software.
Courtesy George Heron, N2APB
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Seen above is a 25 KHz spectrum during a “Pileup”. This program simultaneously
detects and decodes up to 128 Morse Code signals, finds and decodes the amateur
radio call signs simultaneously across the displayed spectrum
Use of this program has been banned from use in many amateur radio contests due
to providing too great an advantage. CW Skimmer can be downloaded here
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•
•
The Undisputed King!
Used to conduct realtime
Keypoard to keyboard text
chat
•
•
•
Invented by Peter Martinez
(G3PLX), Debuted in 1999
Most popular HF digital mode
Heard near: 3.580, 7.070, 14.070, 21.070
MHz
• “Phase Shift Keying” is the the most popular of the newer digital modes.
• Wealth of information on the web regarding BPSK (Binary PSK) and QPSK
(Quadrature PSK)
• Because bandwidth only 31Hz, many signals can fit into the same bandwidth
occupied by an SSB signal (2.4kHz approx.).
• Quite common to see 15 or more signals on a 2.5kHz waterfall display.
Courtesy George Heron, N2APB
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•
•
•
•
•
Developed originally as part of the WSJT weak signal modes software package
by Joe Taylor, K1JT, but is now open source
Can also be decoded by other packages, such as MultiPSK.
Has found a use on HF and can be found around 14.076MHz and 21.076MHz
amongst others.
Signals that are virtually inaudible can give perfect copy so its performance is
excellent on the noisy HF bands.
Transfer rate is slow, as are most modes that excel in low signal decoding.
Courtesy George Heron, N2APB
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Software Defined Radio
Software Demos:
(Video, HDSDR)
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DK3QN Example self-extracting WINRAD software and .wav files with instructions
HDSDR (former WinradHD) is an advanced version of Winrad
SDR Sharp a simple, small and fast PC-based DSP application for Software Defined
Radio. It’s written in C# with both object design correctness and performance in mind
Signals, Samples and Stuff, a DSP tutorial parts 1, 2, 3, and 4 QEX Mar April 1998
Comparison of “conventional”, “DDC based” and “soundcard based” receivers
Quadrature Signals, complex, not complicated on the DSPGURU.com site
Soundcard SDR Software
Virtual Audio Cable software by Eugene Muzychenko [ $35]
Software Defined Radio Explained – Fists of Fourier Parts 1, 2, 3, and 4 explains how
the QSD detector works
VSP manager by Steve Nance - virtual com port software, free but requires amateur radio
call sign)
FLDIGI digital mode software
Digipan for PSK31 and PSK63
Ham Radio Deluxe, a widely used comprehensive program suite for CAT control, and
digital modes
MultiPSK digital mode software
The VITA Radio Transport Protocol for SDR architectures future standard in work
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