software defined radio for beginners
TRANSCRIPT
Software Defined Radio
for Beginners
July 19, 2014
Stephen Hicks, N5AC
VP Engineering, FlexRadio Systems
SDRs for BeginnersAgenda
What is an SDR?
History of Amateur SDR
Technologies that make an SDR
Examples of SDRs
Benefits and uses of SDRs
What is an SDR?
What is an SDR?
What is an SDR?
SDR is a spectrum
Some radios are clearly NOT
Other radios clearly ARE
Many permutations is-between
So what makes up an SDR?
Back to Basics …
RadioMagic
Back to Basics …
LO
DEMOD
FILTER IF AMP
AUDIO AMP
MIXER
Multi-Conversion
64.455 MHz 455kHz
36kHz
3–15 kHzRoofing Filter
Distortion
DEMOD
Engineering Design Process
Draw a block diagram
Simulate
Draw a schematic
Simulate
Build
Measure and adjust
Engineering Design Process
Does the circuit match the simulation exactly?
NO … WHY?
Components are not “ideal”
There are losses not modeled
Component variance
Component capabilities
Result: Never as good as the simulation
Can’t we account for component differences?
In some cases, YES
Some materials work better in some cases
Compensating circuits can be added
In some cases, NO
There will always be issues
Components and Problems
Resistors
Capacitors
Inductors
Transistors
Mixers
Amplifiers
Crystals
Filters
Lot VarianceParasiticsNon-linearitiesThermal varianceElectrically induced varianceIMDManufacturing varianceThe list goes on…
Filtering: The Goal
“Brick Wall” Filter
frequency
resp
onse
Block undesired
Pass desired
FilteringPractical limits to achievable results
Suggested capacitor model, Tantalum capacitor
Block Diagram Key
Yellow blocks are
Green blocks are
DIGITAL
ANALOG
1233467671134
00110101011110010
45591321
239423
Filter Design: Simulation
Sampled signals passed through simulated ideal components
Results could even be played out a speaker
123346767113415821204895431208
150300600120015001200600300150
FILTERSIMULATION DAC
Filter Design: Simulation Limits
Analog: 20-30 poles
Digital: unlimited … except for latency. Maybe 200, 1000, more!
Could a computer run the simulation IN THE RADIO?
ADC DACFILTER
SIMULATION
Presto: Software in the Radio
LO
DEMOD
FILTER IF AMP
AUDIO AMP
MIXER
FILTER
Is this an SDR?
ADC DAC
DEFINITIONS: Software Defined vs. Controlled
CONTROLLED
Computer Control of Fixed Capabilities
(frequency, band, etc)
DEFINED
Modulation, Demodulation, filtering, and processing; as
well as Control Capabilities Software Defined and
Upgradeable
Filter Shape Factor
FLEX-5000Note Brick Wall & Flatness
Radio Y
Radio Z
Radio X
500 Hz Brick Wall Filter
6dB Bandwidth 487 Hz, 60dB Bandwidth 660 Hz, Shape Factor ~1.35
4096 Bin FFT and 2048 Tap Filter
2.8KHz SSB Filter Spectrum
6dB Bandwidth 2587 Hz, 60dB Bandwidth 2756Shape Factor ~1.06, 2048 Tap Filter
Software Demodulation
LO
DEMOD
FILTER IF AMP
AUDIO AMP
MIXER
FILTER
Now, is this an SDR?
ADC
DAC
Software Demodulation and Baseband
New demod schemes added later!
Precise Filtering
Advanced Noise Reduction
DEMOD
IF AMP
AUDIO AMP
FILTER DAC
ADC
PowerSDR - A FlexRadio Original!
Economics 101
What is the marginal cost of a 2nd receiverin an analog radio?
ANSWER: the cost of the added parts (plus amortized engineering)
What if I want 2 RX?
LO
DEMOD
FILTER IF AMP
AUDIO AMP
MIXER
FILTER
2x analog components ≈ $2x
ADC
DAC
DEMODADC
FILT
ER
What are we trying to achieve?
Remove distortion
Better performance
Flexibility to change or add features
Ability to tailor the radio quickly
Never before possible noise mitigation
Never before possible capabilitiesCan we do more?
LO
DEMOD
FILTER IF AMP
AUDIO AMP
MIXER
FILTER
What about this analog stuff?
DAC
ADC
Direct Sampling
LO
DEMOD
FILTER
AUDIO AMP
MIXER
FILTER
Now, THAT’s an SDR!
DAC
ADC
LO
DEMOD
FILTER IF AMP
AUDIO AMP
MIXER
FILTER
Why doesn’t everyone do Direct Sampling?
192kHz @ 64bits =12Mbps
192kHz
DAC
ADC
10Mbps
Direct Sampling
LO
DEMOD
FILTER
AUDIO AMP
MIXER
FILTER
Now, THAT’s an SDR!
250MHz @ 16bits =4Gbps
250MHz
DAC
ADC
4Gbps is…
40 - 100Mbps cables4 - 1Gbps cables
That’s a LOT of data!The most modern home networking you can buy, can’t handle this …
Direct Sampling Benefits
+ Distortion minimized (ADC @ antenna): best signal clarity
+ n-Receivers, n-Panadapters and varying widthssee more bands, more receivers
+ Extremely high dynamic range: operate in worst conditions
+ Extreme flexibility through reprogrammability (ultimate SDR): future benefits
– Technically challenging to design
Economics 101
What is the marginal cost of a 2nd receiverin an digital radio (SDR)?
ANSWER: the cost of the extra processing power (plus amortized engineering) … think Moore’s law
Processing Power = FPGA
Direct Sampling
LO
DEMOD
FILTER
AUDIO AMP
MIXER
FILTER
Now, THAT’s an SDR!
ALL of HF digitizedALL of HF
DAC
ADC
Direct Sampling
NCO
DEMOD
FILTER
AUDIO AMP
MIXER
How many do you want?
DAC
ADC
DEMOD
FILTER
MIXER
We are called to be the architects of the future, not it’s victims
—R. Buckminster Fuller
Design Options:#1: ADC and a hose
Radio is ADC FPGA Ethernet⟹ ⟹
Leverage PowerSDR; minimal SW investment
ADC FPGA PC
RADIO
Pros & Cons for Remote Processing
+ Lots of DSP Power in Computer: easy, ubiquitous+ Plenty of expertise available
– Requires a computer always on– Control via RDP / VNC / GotoMyPC, etc.
– Audio via Skype, etc.– Hard and not particularly bandwidth friendly
Direct Sampled - Remote
HPSDR Hermes
HPSDR
RF DSP DSP CTRL
ANAN-100D
RADIO
Design Options:#2: ADC + FPGA + DSP/uP
Radio reduces bandwidth to minimum before Ethernet
Oh gosh: start over with SW: big investment!
ADC FPGA
PC/OTHER
CHLBB
DSP
Integrating the Baseband ProcessorKey Benefits
Consistent performance independent of PC
Minimized network bandwidth (think remote)
Minimization of “system” problems
Self-contained, rapid startup platform
Spectrum displays (panadapter) independent of available network bandwidth
Example Third GenerationSDR Architecture
dd
7.9Gbps + 1Gbps
Spectrum Display BW
1MHz<500kbps
1MHz77Mbps
150:1BandwidthDifference
10MHz<500kbps
1500:1BandwidthDifference
10MHz770Mbps
Multi-mode Waterfall
Waterfall plus Bandscope
Ionosonde trails
CW Skimmer x4
Digital Modes
More Functional Displays
WSPR times 4!
EasyPAL
TX6G: A Picture is worth 1,000 words