SDR SOFTWARE DEFINED RADIO NARC PRESENTATION - JANUARY 2016 STEPHEN OLESEN - VE6SLP

SDR
        SOFTWARE DEFINED RADIO
NARC PRESENTATION – JANUARY 2016
         STEPHEN OLESEN – VE6SLP

WHAT IS SDR?

• SDR – Software Defined Radio
• Instead of using discrete components or dedicated ICs for tuning, reception and demodulation,
  software may take on many of these roles.
• Hardware component tends to only provide RF to IF conversion (including a zero-IF).
• Uses software to demodulate received signals.
• Uses software to modulate transmitted signals.

WHY USE SDR?

• SDR provides flexibility by removing restrictions imposed by hardware in the signal chain.
• A single RF frontend can be used by multiple signal processors as the incoming RF is digitized early on in
  the process.
• General purpose computers can be used with high performance to analyze and work with complex
  signals or multiple (independent or dependent) signals at once.
• Digitization of the RF signal in both directions allows for very accurate reproduction and analysis of
  signals without introducing further noise in analog components.

BASIC CONCEPTS
HARDWARE COMPONENTS

• The hardware involves:
    •   An RF frontend, generally can be quite wideband and often found as a monolithic IC.
    •   Analog to digital conversion, either from an IF or from baseband.
    •   In a transmitter, a digital to analog converter is also used.
          •   May send baseband to an IF mixer or direct to RF.

• Components are simpler as less amplification needs to take place before the ADC, filtering and
  processing are done digitally in software.

BASIC CONCEPTS
SOFTWARE COMPONENTS

• The software only needs to work with a digital stream of data which is the RF data converted from the
  RF frontend.
• Software can receive real samples or complex samples (I/Q – in-phase/quadrature).
• Can run as a service, as a user application, in dedicated hardware (such as FPGAs, DSPs or even
  Arduinos/microcontrollers).
• Data can be transmitted digitally over networks without loss of signal fidelity.

BASIC CONCEPTS
SOFTWARE
• Examples of software include:
    •   SDR# (SDR Sharp, Windows)
    •   SDR-Console (Windows)
    •   HDSDR (Windows)
    •   GNU Radio (Linux)
    •   Linrad (Linux)
    •   SDR-Shell (Linux)
    •   Gqrx (Linux, Mac)
    •   WebSDR (Linux, provides web interface to multiple users)

BASIC CONCEPTS
RF DIGITIZATION
• The RF is received on an antenna.
• RF frontend usually provides normal frontend filtering (bandpass, low pass, etc.)
• RF is either directly mixed to baseband or to an IF
    •   IF is either directly sampled or mixed to baseband
• Samples are sent to the computer as either real or complex samples
    •   Real can be converted to complex, and vice versa
• Baseband can easily be sampled with a computer sound card
• IF generally requires dedicated hardware for the conversion of the high frequency IF
• Receive bandwidth limited by the analog to digital converter (or sound card)

BASIC CONCEPTS
DEALING WITH THE DIGITAL SIGNAL
• The real samples generally are converted to I/Q samples, providing a 90 degree out of phase sample of
  the RF data
• The complex sample is able to produce amplitude and phase across the entire received spectrum while
  eliminating images due to mixing
• Real samples when converted have no direct phase information and will have an image signal present
  after conversion
    •   This can be removed using digital filters
• Digital signal can be sent through extremely complex or many-poled filters providing sharp, narrow
  filters on the raw RF data
• Original signal data can be used in multiple filters/demodulators simultaneously across the entire
  received bandwidth.

BASIC CONCEPTS
SAMPLING RATE, NUMBER OF BITS, BANDWIDTH

• Since the RF signal is digitized, the analog to digital conversion will have a fixed sample rate.
• Depending on the hardware (ADC and DAC), this sampling rate may be at sound card speeds (48 or
  96kHz, or 96kSPS/192kSPS) or higher (such as the BladeRF at 40MSPS)
• Usable bandwidth is half the sampling rate (192kSPS provides 96kHz bandwidth, 40MSPS provides
  20MHz bandwidth)
• Bit length provides the total signal amplitude range and relates strongly to the achievable SNR, dynamic
  range, accuracy and overload characteristics. 8 bits is common, providing 256 levels of signal strength.

COMMON HARDWARE
RTL-SDR

•   Simple USB devices known as RTL-SDR (RTL2832) are easy to find and a low cost way to experiment with reception only SDR.
•   Available in Canada for as low as $15, but generally in the range of $25-$30.
•   Available with a variety of tuner chipsets, most common these days is the R820T.
•   Connects via USB to a computer.
•   Able to tune from around 50MHz to 1.5GHz and above.
•   Provides 8 bit samples at up to 3.2 MSPS (usually only usable up to 2.4MSPS or so)

COMMON HARDWARE
SOFTROCK

•   The Softrock series by Five Dash (KB9YIG) are a kit version of HF SDRs which use a computer sound card for
    the digitization portion.
•   Low cost and a simple design allow a good understanding of the hardware side of SDR.
•   Range in price from $21 USD to around $100 USD.
•   Use USB for power and frequency control, regular 3.5mm audio cables for the baseband audio to be digitized.
•   Compatible with a wide variety of software as the only requirement is the sound card driver.
•   Capable of both transmission (low power, around 1 watt) and reception, 96kHz bandwidth (192kSPS)

COMMON HARDWARE
FLEX SDR

• Flex Radio provides all-in-one solutions for high end performance.
• A combination of hardware based digital processing and computer based signal processing.
• Higher power outputs than the SoftRock.
• Range in price from $1000 to $11,000.
• Familiar rig layout and design with many input and output options.
• NARC owns a Flex Radio SDR at the shack.
• Some support dual RF frontends, wide bandwidth (not limited by a computer sound card)

ADVANCED HARDWARE
BLADERF AND HACKRF
•   Both the BladeRF and HackRF are small USB controlled SDR hardware frontends.
•   Provide onboard ADC and DAC.
     •   BladeRF capable of full duplex communication.
•   Very low output powers (10mW or less).
•   BladeRF is capable of 40MSPS and 300MHz to 3.8GHz transmit/receive, 12 bits.
•   HackRF is capable of 20MSPS and 1Mhz to 6GHz, 8 bits.
•   BladeRF runs around $600-$1000 USD, HackRF is around $350-450 USD.
•   BladeRF has an onboard FPGA, HackRF uses a CPLD.
•   Designed for experimentation, protocol design, advanced decoding.
•   They have been used to provide GSM/LTE cellular network services, digital TV (ATSC) transmission, and more.

USING WHAT YOU HAVE
ANY RIG USING A SOUND CARD
• Since the real idea of SDR is that software handles all the signal processing, any RF frontend can
  theoretically be used to get the signal into the software.
• Using a normal radio (HF, VHF, UHF, etc.) with an audio connection to a computer can provide low-
  bandwidth SDR services.
• Bandwidth limited by the in-radio filters (USB, LSB, FM, etc.)
• This sort of setup is commonly found with PSK, JT65, WSPR.
• The RF frontend is a full radio capable of demodulation of audio, but is unaware of what that audio is.
  The computer then processes the input like an SDR to provide these digital modes.
• Fldigi and Ham Radio Deluxe provide convenient interfaces to classic radios via the sound card (and
  often a connecting interface to provide PTT and level control).

INTERFACING
USB AND SOUND CARD INPUTS

• The simplest SDR RF frontend outputs the baseband signal via regular analog audio signals to a
  computer’s sound card.
    •   Limited bandwidth (audio bandwidth ranges).
    •   I/Q imbalance is more common and harder to fix.
• USB inputs vary, with devices like the RTL-SDR, Flex, BladeRF and HackRF having integrated ADCs/DACs.
    •   Some USB SDR devices use built-in soundcards which connect over USB, but are still limited to audio ranges.
        The RigBlaster series is an example of an SDR-like interface with integrated sound card.

COST OVERVIEW

• Starting with equipment you already have, experiencing the basics of SDR and the integration of
  computers with radios, can cost nearly nothing.
• Using an RTL-SDR based USB adapter can get you up and running for under $25.
• Adding on transmit capabilities can start as low as $70 for the SoftRock, up to the Flex Radio series at
  many thousand of dollars.
• Because the RF portion is relatively straight forward, designing your own SDR frontend can be done (this
  generally involves oversampling your desired frequency to get I/Q samples and mixing with an IF to
  convert to baseband, and not much else).

RF CHARACTERISTICS

• In general, SDR provides for a clean output signal.
• Sharp and complex filters can be used in software to remove as much extra sideband/noise as possible.
• Extremely complex signals can be sent digitally to a high performance DAC which produces the voltage
  output to the RF transmitter without needing complex analog filters or integration to join multiple
  signals together.
• Signal noise is influenced by the bit size and sample rate used to generate the signal.
• Since the RF frontend is straightforward (ADC/DAC, mixer and amplifier), the signal path is short,
  preventing extra oscillators and parasitics from compromising the signal.

SOME EXAMPLE USES

• ADS-B (1090MHz) plane transponder tracking
• Multi-channel trunking scanners
• Wideband band listening / waterfall (including multi-user demodulation), ie. WebSDR
• Remote listening / transmitting
• PSK, JT65, WSPR (all at the same time, with one antenna and SDR front end)
• Experimental digital or analog mode design
• Satellite tracking and telemetry
• Discovering the RF world around you without spinning the dial (a wide bandwidth receiver showing
  20MHz of RF spectrum at once gives a nice overview of nearly all the HF spectrum at once)

QUESTIONS?

• Or feel free to send me questions at ve6slp@narc.net