Learning DSP and SDR Hack Chat

To the frequency domain, and beyond

Wednesday, November 11, 2020 12:00 pm PST Local time zone:
Hack Chat
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Marc Lichtman will host the Hack Chat on Wednesday, November 11, 2020 at noon Pacific Time.

Time zones got you down? Here's a handy time converter!

Join Hack Chat"Revolution" is a term thrown about with a lot less care than it probably should be, especially in fields like electronics. It's understandable, though -- the changes to society that have resulted from the "Transistor Revolution" or the "PC Revolution" or more recently, the "AI Revolution" have been transformative, often for good and sometimes for ill. The common thread, though, is that once these revolutions came about, nothing was ever the same afterward.

Such is the case with software-defined radio (SDR) and digital signal processing (DSP). These two related fields may not seem as transformative as some of the other electronic revolutions, but when you think about it, they really have transformed the world of radio communications. SDR means that complex radio transmitters and receivers, no longer have to be implemented strictly in hardware as a collection of filters, mixers, detectors, and amplifiers; instead, they can be reduced to a series of algorithms running on a computer.

Teamed with DSP, SDR has resulted in massive shifts in the RF field, with powerful, high-bandwidth radio links being built into devices almost as an afterthought. But the concepts can be difficult to wrap one's head around, at least when digging beyond the basics and really trying to learn how SDR and DSP work. Thankfully, Dr. Marc Lichtman, an Adjunct Professor at the University of Maryland, literally wrote the book on the subject. "PySDR: A Guide to SDR and DSP using Python" is a fantastic introduction to SDR and DSP that's geared toward those looking to learn how to put SDR and DSP to work in practical systems. Dr. Lichtman will stop by the Hack Chat to talk about his textbook, to answer your questions on how best to learn about SDR and DSP, and to discuss what the next steps are once you conquer the basics.

Banner image credit: Dsimic, CC BY-SA 4.0, via Wikimedia Commons

  • Hack Chat Transcript, Part 3

    Dan Maloney11/11/2020 at 21:07 0 comments

    perronemajr12:59 PM

    I mean without

    Chris Weiss joined the room.12:59 PM

    Marc Lichtman12:59 PM
    do you mean SDR hardware project?

    Marc Lichtman1:00 PM
    like community-lead open source hardware

    OK, that was a jam-packed hour! Gonna be a chore to get this transcript posted, that's for sure. But that's a good problem to have. I want to thank Marc for being here today and for this informative and fun Hack Chat. I really appreciate the time today, Marc, thanks so much. And to everyone who attended, same to you -- you made this a great Hack Chat! Feel free to keep the chat going, of course - the Hack CHat is always here for you!

    Don't forget that next week we have a Chat that was rescheduled from October:

    Marc Lichtman1:00 PM
    check out


    Harnessing Your Creativity Hack Chat

    Leo Fernekes will host the Hack Chat on Wednesday, November 18, 2020 at noon Pacific Time. (Note that this is rescheduled from the original 10/14 date -- we had a little time zone snafu. -- ed) Time zones got you down? Here's a handy time converter!

    Read this on Hackaday

    Marc Lichtman1:00 PM
    Yeah glad to have hosted a Hack Chat!

    manoeldesouza1:00 PM
    Hello everyone. Are there SDR software dedicated for digital signals decoding?

    Marc Lichtman1:00 PM
    thanks for having me

    Marc Lichtman1:00 PM
    GNU Radio! =)

    Jeffrey Forbes1:01 PM
    Pulse NMR, Apply a transmitter pulse then receive the emitted signal

    Collin Avidano1:01 PM
    Thank you!

    Aaron1:01 PM
    Thanks Marc!!!

    Marc Lichtman1:01 PM
    GNU Radio has flowgraphs/blocks for many different comms protocols

    Jeffrey Forbes1:01 PM
    Thanks Marc

    Simon joined the room.1:01 PM

    Aaron1:01 PM
    ...and everyone else for their comments!

    Marc Lichtman1:01 PM
    Yeah I didn't realize this awesome community existed, I had just known about hackaday from the articles

    manoeldesouza1:01 PM
    Thanks. need to check that.

    Chris Weiss1:01 PM
    @Marc Lichtman - If you're asking about the user-side, ADSB/FlightAware has a lot of folks contributing radio telemetry of aircraft locations

    fid1:02 PM
    thank you @Dan Maloney and @Marc Lichtman I took notes and downloaded a few things.

    kiggins.chris1:02 PM
    Thanks marc! Github is the best way to keep the discussion then?

    Marc Lichtman1:02 PM
    feel free to check out the textbook,, I just recently finished the first version so there might be room for improvement, and I'm always looking for help

    RoGeorge1:02 PM
    @Marc Lichtman IMO, Open Hardware is more of a myth, it will never take of, like Open Software, so don't put much hope in an open HW SDR.

    @fid -- I'll be posting a transcript in a few minutes in case you missed anything

    Thomas Shaddack1:02 PM
    how different (for learning the very basics) is DSP for audio and for rf?

    Marc Lichtman1:02 PM
    yeah email me at or use github

    perronemajr1:02 PM
    @Jeffrey Forbes Thanks!

    Chris Weiss1:02 PM
    Oh, sorry, that was @Aaron 's question

    Marc Lichtman1:02 PM
    "how different (for learning the very basics) is DSP for audio and for rf?" tons of similarities

    Marc Lichtman1:02 PM
    but when you get into comms stuff its all new

    fid1:03 PM
    thanks @Dan Maloney

  • Hack Chat Transcript, Part 2

    Dan Maloney11/11/2020 at 21:05 0 comments

    Marc Lichtman12:28 PM

    Ettus support is fantastic from my experience

    Marc Lichtman12:28 PM
    and I don't have any affiliations with them

    Marc Lichtman12:29 PM
    and LimeSDR support has been like super bad, I had a couple bricked Limes early on

    perronemajr12:29 PM
    And part of that: is there a good way to map out the power output as a function of frequency?

    Marc Lichtman12:29 PM
    from my experience

    miek12:29 PM
    @Aaron a lot of FPGAs include DSP blocks that are good for implementing FIR filters

    Marc Lichtman12:29 PM
    sorry if there are Lime folks here

    Marc Lichtman12:29 PM
    I'll have to look into that NMR app later

    Marc Lichtman12:29 PM
    hadnt seen it before

    Marc Lichtman12:30 PM
    keep in mind, when someone uses a certain SDR for a certain app, 99% of the time they could have used a different SDR

    Marc Lichtman12:30 PM
    so it really comes down to being familiar with the API

    Marc Lichtman12:30 PM
    and having code examples and such

    perronemajr12:30 PM
    NMR is super useful for my work so it def caught my attention

    Thomas Shaddack12:30 PM
    looks like there's a range of possibilities with various rf-freq measurement of materials.

    Marc Lichtman12:30 PM
    yeah I wouldn't put much emphasis on the LimeSDR part

    Marc Lichtman12:30 PM
    they probably could have used several other SDRs

    perronemajr12:30 PM
    Point taken

    Marc Lichtman12:30 PM
    SDRs are very general purpose

    Aaron12:31 PM
    Will this chat transcript be available later?

    @perronemajr - Any idea how old that NMR article is? Might make a good Hackaday writeup if it's still pretty fresh.

    Marc Lichtman12:31 PM
    and like I said, the way I usually use them is to deliver the baseband IQ samples to my host machine, where they get processed

    perronemajr12:31 PM
    That's why I asked if there was a good way of mapping the power output

    Marc Lichtman12:31 PM
    I only rarely modify the FPGA on the SDR itself

    perronemajr12:31 PM
    because if you can map it out for hackrf one then you can use that instead

    @Aaron - Yes, absolutely. I'll post it right after the chat.

    Marc Lichtman12:31 PM
    yeah and another SDR uses the same FPGA or RFIC then there's less work to do

    Aaron12:31 PM
    Great, Thanks! Some of us are still at work.. shhhh... =)

    clint.cole12:31 PM
    Thanks Dan

    Marc Lichtman12:31 PM
    or if the app didn't involve modifying the FPGA, you can probably sub them out with little effort

    Marc Lichtman12:32 PM
    like if all the DSP is happening on the host machine, its easy to swap SDRs

    Marc Lichtman12:32 PM
    the SDR is just a frequency-agile receiver (or transmitter) in that case

    perronemajr12:32 PM
    I think it did modify the FPGA, according to the paper written

    Marc Lichtman12:32 PM

    perronemajr12:32 PM
    Will check again though

    Marc Lichtman12:32 PM
    so then you would want to check how big an FPGA is needed

    perronemajr12:32 PM
    And look for ways around

    Marc Lichtman12:32 PM
    like the PlutoSDR has almost no room left on the FPGA for custom stuff

    Marc Lichtman12:32 PM
    but USRP B210 I think has a lot of room

    Marc Lichtman12:33 PM
    not sure about HackRF

    Marc Lichtman12:33 PM
    bigger FPGAs cost a lot more

    Marc Lichtman12:33 PM
    so when you see more expensive SDRs, that might be one reason, larger FPGA

    Marc Lichtman12:33 PM
    I like to do my DSP on the host side, for the sake of rapid development

    Marc Lichtman12:33 PM
    but if you need to do some DSP at "high rate", sometimes it has to be done on the FPGA

    perronemajr12:33 PM
    What's a good budget SDR with an FPGA at least as large as the one lime has?

    Barry Duggan12:34 PM
    using GNU Radio, I swap between USRP B200mini and a Pluto with almost zero effort for transmit and receive

    Marc Lichtman12:34 PM
    yeah GNU Radio is all about doing DSP on the host, until you get into RFNoC

    Marc Lichtman12:34 PM
    I dont know exactly how large the Lime's is, but considering the price its probably on the smaller end

    Marc Lichtman12:34 PM
    you can see how many LUTs or however they measure the size of the FPGA

    Michael Brown joined the room.12:34 PM

    Marc Lichtman12:35 PM
    its an...

    Read more »

  • Hack Chat Transcript, Part 1

    Dan Maloney11/11/2020 at 21:04 0 comments

    OK all, big crowd today. A warm welcome to all of you who came over via, and to everyone else. I'm Dan, a staff writer here at Hackaday, and I'll be the mod today for Dr. Marc Lichtman as we dive into Learning SDR and DSP!

    Welcome, Marc! Can you tell us a little about your background to start us off?

    clint.cole joined the room.12:01 PM

    Marc Lichtman12:01 PM

    Marc Lichtman12:02 PM
    My name is Marc Lichtman and I wear three different hats- 1) I'm an adjunct prof at University of Maryland, within the CS dept, where I teach a course on hands-on SDR, 2) I'm one of the leads for the GNU Radio project, a free and open source SDR framework, and 3) I'm a research engineer at Perspecta Labs as my full time gig where I do a lot of SDR, machine learning, and spectrum sensing related work.

    Marc Lichtman12:02 PM
    I recently put together a free online textbook,, to help teach DSP and SDR concepts in a hands-on and less mathy way, compared to traditional textbooks on the topics. It uses Python for all code examples, and there are some PlutoSDR-specific exercises. And it's based off what I learned teaching my course at UMD

    jwahar bammi joined the room.12:03 PM

    Jeffrey Forbes joined the room.12:03 PM

    mikerussia0 joined the room.12:03 PM

    Marc Lichtman12:03 PM
    I think that coders and CS students shouldn't feel like they can't dive into DSP and SDR just because they didn't go through a EE graduate program =P

    Aaron12:04 PM
    I went through an EE graduate program.. I WISH they went this far... ;)

    Marc Lichtman12:04 PM
    a large fraction of the actual work being done in DSP/SDR (and jobs), requires good coders, like your typical CS students

    wildblueyonderman joined the room.12:04 PM

    Marc Lichtman12:04 PM
    hah yeah, you have to be a EE grad student, specializing in wireless/DSP

    How do you find the CS students reacting to a hardware topic that at first seems out of the typical CS wheelhouse?

    Marc Lichtman12:04 PM
    I mean there might be an intro to comms class at the undergrad level, but that's about it

    Marc Lichtman12:05 PM
    well, the CS students I had didn't have any experience related to the topics, so they needed to be slowly introduced in a hands-on way, that involved a lot of code examples and exercises

    Marc Lichtman12:05 PM
    it's very foreign to them

    Marc Lichtman12:05 PM
    luckily, even though an SDR is hardware, what you actually do with it is mostly software

    clint.cole12:05 PM
    My daughter is studying this for her PhD in Electronics Engineering at Stanford

    Mark J Hughes12:06 PM
    What's going to be the next great development in SDR? I know I'm seeing it appear in Amateur radio equipment.

    Marc Lichtman12:06 PM
    ah very nice

    David Tarnoff12:06 PM
    What math background did they have at the point they came into your class?

    clint.cole12:06 PM
    Which is partly why I want to learn about it

    Aaron12:06 PM
    I started reading your book and haven't gotten very far yet, but so far you did an excellent job!

    Stony Yakovac joined the room.12:06 PM

    Nicolas Tremblay joined the room.12:06 PM

    Marc Lichtman12:06 PM
    Not sure what the next great development is, depends if you are looking at low cost SDRs, or like space-hardened, or stuff focusing on hams

    Barry Duggan12:06 PM
    I second that!


    PySDR: A Guide to SDR and DSP using Python

    Read this on Pysdr

    Marc Lichtman12:07 PM
    but usually ham stuff is at lower sample rates, and it's all about the antenna, from my little xp

    Marc Lichtman12:07 PM
    so you dont need like the latest and greatest SDR that can do 200 MHz instantaneous bw

    Dave Sanderman joined the room.12:07 PM

    Aaron12:07 PM
    What SDR platforms do you use and what can you recommend?

    Marc Lichtman12:07 PM
    As far as math bg, my course wasn't too mathy so what they had was enough

    Mark J Hughes12:07 PM
    @Marc Lichtman I have no actual use case. I just like to learn :)

    Barry Duggan12:08 PM
    HF bands for hams are not covered very well with existing hardware

    Marc Lichtman12:08 PM
    I personally...

    Read more »

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