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