Software Defied Radios Basic Desigi FARA Nov. 2017 1 / 71 Outliie - - PowerPoint PPT Presentation

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Software Defied Radios Basic Desigi FARA Nov. 2017 1 / 71 Outliie - - PowerPoint PPT Presentation

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Software Defied Radios Basic Desigi FARA Nov. 2017 1 / 71 Outliie Superhet Analog Radio Example for background Direct Conversion Receivers Early Digital Implementations Direct Down Conversion Digital Implementations Direct

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Software Defied Radios Basic Desigi

FARA Nov. 2017

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Outliie

  • Superhet Analog Radio Example for background
  • Direct Conversion Receivers

– Early Digital Implementations – Direct Down Conversion Digital

Implementations

  • Direct Conversion Transmitters

– Direct Up Conversion Digital Implementations

  • Example SDR Transceiers
  • Speculation on Future SDRs
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Backgrouid: K3 Multi-stage Superhet

  • Even analog K3 uses Digital Signal Processing for

noise blanking and limiting, AGC, amplifcation, fltering, and demodulation.

  • K3 Panadapter, the P3, is really a SDR.

BPFs

X

VCO 9-46 MHz Crystal BPFs IF Out to P3 2nd LO

X

8.23 MHz Noise Blanker LPF 15 kHz BW ADC DSP DAC/ LPF/ Amp

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K3 Block Diagram

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Backgrouid Aside: P3 is a SDR

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Direct Coiversioi Reciever

  • Single mixer stage translates a spectrum at RF

down to 0 Hz.

  • Simple structure is well matched for digital

implementation, several implementation options.

Mixer Stage RF Local Oscillator f BASE IN = N MHz f BASE OUT = 0 Hz Demodulation, Panadapter, etc. f BASE IN

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Image Problem

RF Local Oscillator f BASE IN = N MHz f BASE IN

X

f BASE OUT = 0 Hz LPF

  • Input spectrum just below f BASE IN is also mapped to
  • utput.
  • Sharp pre-mixer BPF to remove problem spectrum is

difcult

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Image Problem

  • sin A x sin B = ½ (cos (A – B) – cos (A + B) )
  • sin (2 (f BI+ ) t) x sin (2 f BI t) =

½(cos (2  t) – cos (2 (2f BI+ ) t))

  • sin (2 (f BI- ) t) x sin (2 f BI t) =

½(cos (-2  t) – cos (2 (2f BI- ) t))

  • We can not distinguish between cos (-2  t) and

cos (2  t) in the output.

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Backup: Plot of Cosiie

Symmetric around Y axis X=/2 X=-/2

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Image Reject Architecture

LO f BI

X

90 delay 90 delay

X

+ RF

  • Mixing with both cosine and sine provides

enough information to distinguish between desired signal and undesired image.

  • 2nd 90 delay should be frequency independent
  • ver desired freq range. Digital FIR can be close.

Incident Quadrature 0Hz-based spectrum

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Processiig of sii(2 (f BI+ ) t)

  • I: sin (2 (f BI+ ) t) x sin (2 f BI t) =

½(cos (2  t) – cos (2 (2f BI+ ) t))

  • Q: sin (2 (f BI+ ) t) x sin ((2 f BI t) - /2) =

½(cos ((2  t) + /2) – cos ((2 (2f BI+ ) t) - /2))

  • Q delayed by /2:

½(cos (2  t) – cos ((2 (2f BI+ ) t) - ))

  • I + (Q delayed): cos (2  t)
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Processiig of sii(2 (f BI- ) t)

  • I: sin (2 (f BI- ) t) x sin (2 f BI t) =

½(cos (2  t) – cos (2 (2f BI- ) t))

  • Q: sin (2 (f BI- ) t) x sin ((2 f BI t) - /2) =

½(cos ((2  t) - /2) – cos ((2 (2f BI- ) t) - /2))

  • Q delayed by /2:

½(cos ((2  t) - ) – cos ((2 (2f BI+ ) t) - ))

  • I + (Q delayed): 0
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Digital Implemeitatioi Where to digitize?

  • In the early days, 2000?, low-cost ADCs could not

support the complete 0-30 Mhz bandwidth.

LO f BI

X

90 delay 90 delay

X

+ RF I Q > 16bits x (2x30) Msps 0Hz-based spectrum

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Digital Implemeitatioi Early Geieratioi SDR Receivers

  • Flex SDR-1000, Softrock
  • KX3: similar but all digital processing on-board

LO f BI

X

90 delay

X

RF I Q LPF LPF ADC ADC Digital Processing: Panadapter Noise Filters Demodulation Analog Components PC Sound Card PC Software PC Sound 2 x (16 to 18) bits x (44 to 192) ksps

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Softrock

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Flex SDR 1000

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Elecraft KX3

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Early Geieratioi SDR Receivers Advaitages aid Issues

  • Simple Hardware with few components
  • Hard to precisely match I & Q amplitude & phase,

though digital comp for fxed diferences possible

LO f BI

X

90 delay

X

RF I Q LPF LPF ADC ADC Digital Processing: Panadapter Noise Filters Demodulation Analog Components PC Sound Card PC Software PC Sound

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Digital Implemeitatioi Better Cheap ADCs

  • ADCs good-enough now for entire HF bandwidth,

though some issues which we will discuss later

  • But can‘t get whole 1Gbps rate in/out of uP chip

LO f BI

X

90 delay 90 delay

X

+ RF I Q LPF ADC > 16bits x (2x30) Msps

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Digital Implemeitatioi Direct Dowi Coiversioi

  • FGPA DSP; anti-alias LPF I/Q, reduces sample rate

to min needed for panadapter and demodulation

LO

X

90

X

RF Q LPF ADC I Digital Processing: Panadapter Noise Filters Demodulation PC Software PC Sound FPGA RF Analog 2 x 24 bits x 192 ksps 16 bits x 122.88 Msps Example: openHPSDR Hermes LPF Decimate LPF Decimate

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Backup: Decimate Alias Issue, /2 Decimate Example

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Direct Dowi Coiversioi FPGA Processiig

X X

Q CIC I Example: openHPSDR Hermes cosine sine CORDIC NCO CFIR

LPF & decimate by 320 LPF, decimate by 2, & fix slope

CIC CFIR

LPF & decimate by 320 LPF, decimate by 2, & fix slope

16 bits x 122.88 Msps 2 x 24 bits x 192 ksps

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Direct Dowi Coiversioi FPGA Processiig (coitiiued)

  • COordinate Rotation DIgital Computer

uses just add, subtract, lookup, and bit shift successive approximation used in early calculators such as HP35

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Direct Dowi Coiversioi FPGA Processiig (coitiiued)

  • Does LPF, good at attenuating higher frequencies
  • Does most of the decimation
  • Uses only adds and pipeline delays
  • But not fat in pass band

+ Delay + Delay Cascaded Integrator-comb Filter used in Hermes Decimate by 320 Delay

  • ...

Delay

  • 10 Integrate Stages

running at 122.88 Msps 10 Comb Stages running at 384 ksps ...

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Direct Dowi Coiversioi FPGA Processiig (coitiiued)

  • Used with Blackman-Harris Window Function to

get sharper roll-of. 100dB attenuation of aliases.

  • Coefcients adjusted to fx passband response.
  • Decimating by 2, only do multiplies every 2nd clk

Compensating Finite Impulse Response Filter used in Hermes Delay X C1 ADD Delay X C2 … 256 stages

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Direct Dowi Coiversioi SDR Receivers/Traisceivers for Ham Baids (leveragiig cell phoie chips?)

  • Perseus receiver ~2007
  • openHPSDR Mercury reciever ~2008

Hermes transceiver ~2010?

  • Anan transceivers (based on openHPSDR) ~2014?
  • Flex 6000 transceivers ~2014?
  • Icom 7300, 7610, R8600
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Direct Dowi Coiversioi Advaitages aid Issues

  • Mixing and fltering done digitally. I/Q amplitude

and phase are very accurately matched. Processing noise can be reduced to arbitrary levels.

  • Performance of volume ADCs sufcient but not

fantastic.

– Wide band ADC SNR may only be ~77dBFS.

Not a real issue since we use narrow

  • bandwidths. ~3dB gain for each factor of 2

decimation.

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Backup: Sigial-to-Noise Ratio

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Backup: Oversampliig aid SNR

Fs/2

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Direct Dowi Coiversioi Advaitages aid Issues (coitiiued)

  • ADC performance (continued)

– Higher resolution can be achieved by the

  • versampling/decimation process. 16-bit or

even 14-bit ADCs can be good enough if they have sufcient linearity.

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Backup: Small Sigial aid No Noise

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Backup: Iicreasiig Resolutioi by Decimatioi

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Backup: Iicreasiig Resolutioi by Decimatioi

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Backup: Iicreasiig Resolutioi by Decimatioi

118.948 118.721

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Direct Dowi Coiversioi Advaitages aid Issues (coitiiued)

  • ADC performance (continued)

– ADC SFDR, Spurious-Free Dynamic Range,

roughly the ratio of a fundamental signal to the strongest resulting spurious signal in the

  • utput, may only be ~94dBc. I think that

decimation process gain does not help since the spurious signal is at a fxed frequency.

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Direct Dowi Coiversioi Advaitages aid Issues (coitiiued)

  • ADC performance (continued)

– The efective dynamic range of the ADC and

the wide bandwidth into the ADC may allow ADC overload. Any signal in passband of the pre-ADC flter can cause overload. Issue can be limited to a particular band by a sharp pre- ADC BPF. For example Flex has put sharper BPFs for contest bands in their new 6600.

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Direct Dowi Coiversioi Advaitages aid Issues (coitiiued)

  • Performance/latency/FPGA size compromises

that I don‘t completely understand in the flters.

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Direct Dowi Coiversioi Advaitages aid Issues (coitiiued)

  • Nonetheless the current crop of high-end SDR

receivers perform as well or better than the best high-end analog receivers on conventional measurements such as Sherwood Engineering‘s dynamic range tests.

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Sherwood List, page 1

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Sherwood List, page 2

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Sherwood List, page 5

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Direct Coiversioi Traismitter SSB Exciter

  • Pretty much reverse of receiver.

LO f RF 90 90

X

  • Audio

I Q

X

USB

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Digital Implemeitatioi Direct Up Coiversioi

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  • peiHPSDR Hermes

Traisceiver

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Example SDR: Aiai 8000

  • Based on OpenHPSDR work
  • Host computer handles DSP after decimation
  • Uses open source SW
  • An input BPF for each band. A set for each ADC.
  • Dual ADCs allow diversity reception. Can

simultaneously listen to 7 frequecncies.

  • 200W 50VDC LDMOS Power Amp
  • PureSignal predistortion fxes PA nonlinearities,

reduces Intermodulation Distortion

  • PiHPSDR Controller available
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Example SDR: Aiai 8000

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Example SDR: Aiai 8000

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Example SDR: IQ2

  • Based on OpenHPSDR work
  • Host computer handles DSP after decimation
  • Uses open source SW, very similar to Anan
  • Only one fxed input LPF
  • One ADC
  • <.5 W Transmit Power
  • No predistortion
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Example SDR: Flex 6700

  • Vendor supported proprietary HW and SW.
  • On-board FPGA and processor handle almost all

DSP.

  • An input BPF for each band. A set for each ADC?

New 6600 has even sharper input flters.

  • Dual ADCs allow diversity reception. Can

simultaneously listen to 8 frequecncies.

  • 100W PA
  • No predistortion?
  • Maestro Controller available
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Example SDR: Flex 6700

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Example SDR: ICOM 7300 & 7610

  • SDR with knobs. On-board everything. FPGA,

DSP processor, graphic display, speaker, etc.

  • An input BPF for each band.
  • 7300, one ADC. Only listen to one frequency at a

time? 7610 will have two ADCs with a set of BPFs for each. 7610 will have higher performance?

  • 100W PA
  • Simpler to set up and use than knob-less SDRs.

But less control of features and fewer features.

  • 7300 is $1,350. 7610 will be ~$3,700?
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Example SDR: ICOM 7300

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Example SDR: ICOM 7300

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Example SDR: ICOM 7300

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Example SDR: ICOM 7300

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Example SDR: ICOM 7300

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Example SDR Receiver: ICOM R8600

  • SDR with knobs. On-board everything. FPGA,

DSP processor, graphic display, speaker, etc.

  • 10 kHz to 3 GHz. DDC below 30 MHz.
  • 11 BPFs for HF. 13 for VHF/UHF.
  • One 14-bit 122.88 Msps ADC.
  • RTTY and D-STAR. I/Q output with future FW.
  • Top-tier noise and dynamic range values in ARRL
  • testing. Dither enabled for DR testing. 30dB gain.
  • ~$2,600
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Example SDR Receiver: ICOM R8600

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Comparisoi: Flex vs Aiai

  • Flex 6700 and Anan 8000 both have good

performance, though the 200W Anan transmitter may have a slight edge on the Flex transmitter.

  • Largest diference is in the SW.

– Flex developes and supports their own

proprietary SW. All the features work well

  • together. Default settings work well. Thus the

Flex radios are easier to setup.

– The Anan radios use open source SW from the

OpenHPSDR community. More set up work but they beneft from the latest flters and features from the community.

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Example of OpeiHPSDR SW Setup Complexity: Audio Iiput

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Comparisoi: Flex vs Aiai (coitiiued)

  • Another diference is the amount of DSP done in

the radio vs what is done in the host computer.

– The Flex radio has a processor on board. The

Flex does almost all the DSP in the radio. The computer client is thin. Easier to support a standalone controller and remote operation.

– The Anan radio needs a thicker client. More

DSP is done outside the radio. However processors are cheap these days. The PiHPSDR Controller with an ARM processor is $600.

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Comparisoi: Flex vs Aiai (coitiiued)

  • The cost of Flex radios and the cost of Anan

radios seem to currently be competitive.

– The Flex 6700 was $7,500. However the new

Flex 6600, which should have most of the important features, will be approximately $4,000. Flex 6600 has built-in ATU.

– The Anan 8000DLE is also approximately

$4,000. Anan 8000DLE has 50V 200W LDMOS PA with predistortion.

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Comparisoi: Flex vs Aiai (coitiiued)

  • The Anan radios are developed by the

international OpenHPSDR community. Flex Radio is a US based company.

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The Future: Sure Thiigs aid Wild Guesses

  • Sure thing

There will be more SDRs including → more SDRs with knobs. The digital approach is or will quickly become the cheapest way to build good performance radios. Your next radio may be a SDR. Current SDR with knob examples are the ICOM 7300, $1,350 and the soon to be available 2-ADC ICOM 7610, ~$3,700?. The 7610 has higher performance than the 7300. ICOM claims ~110dB Reciprocal Mixing Dynamic Range @ 2kHz spacing which is roughly 10dB better than their spec for the 7300.

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The Future: Sure Thiigs aid Wild Guesses (coitiiued)

  • Sure thing (continued)

– By the way I prefer SDRs that provide access to

the control of radio features, particularly the DSP options.

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The Future: Sure Thiigs aid Wild Guesses (coitiiued)

  • Wild guess

Perhaps some day LPF/ADC/DAC →

  • nly radios?

LO

X

90

X

RF Q LPF ADC I Digital Processing: Panadapter Noise Filters Demodulation PC Software PC Sound RF Analog >16 bits x 122.88 Msps LPF Decimate LPF Decimate

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The Future: Sure Thiigs aid Wild Guesses (coitiiued)

  • LPF/ADC/DAC only radios? (continued)

Discussed this with Gerald Youngblood, Flex Radio founder and president.

– He thinks that such radios will not be possible

soon.

– He thinks that even when they are possible

there will still be advantages to doing much of the DSP in the radio. He may be right but I think that there are also advantages to doing almost all the DSP in the host computer.

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The Future: Sure Thiigs aid Wild Guesses (coitiiued)

  • LPF/ADC/DAC only radios? (continued)

– Gerald agreed with my hunch that SW-only

vendors can not make enough money in the Ham radio market.

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Ackiowledgemeits aid Refereices

  • Phil Harman, OpenHPSDR Mercury receiver talk

https://www.youtube.com/watch?v=0LJpD9T1KgE

  • Gerald Youngblood, QEX Articles on SDR 1000

http://www.fexradio.com/downloads/sdr_qex_1- pdf/

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Ackiowledgemeits aid Refereices (coitiiued)

  • An Introduction To HF Software Defned Radio

Andrew Barron ZL3DW

  • Software Defned Radio for ameteur radio
  • perators and shortwave listeners

Andrew Barron ZL3DW

  • OpenHPSDR documentation
  • Apache Labs, Flex Radio, and ICOM product

information

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Ackiowledgemeits aid Refereices (coitiiued)

  • Dan Pedtke ("ped-key"), KW2T

http://danstechnight.com/