6 ms·

Building a software-defined radio from scratch

283 points by dominicgs 10y ago

ericjang 10y ago
This is a really impressive project, and I am all the more in awe that this guy is only 18 years old. The project is on Github: https://github.com/FreeSRP https://github.com/FreeSRP Reddit discussion: https://www.reddit.com/r/electronics/comments/4uic5r/sdr_platform_ive_been_working_on/ https://www.reddit.com/r/electronics/comments/4uic5r/sdr_pla... He's selling a small batch of these for $350 apiece - calling it now, he's going to be very successful in his career.
- laobeylu 10y ago
  Thank you for the kind comment. Not selling them yet, though, and the small batch might end up being a little more expensive than that (but I'm really trying to keep it under $400).
batbomb 10y ago
I think the USRP1 motherboard, when I originally used one in 2008, used to be $700 complete/$550 for the motherboard. The price now is $719, but that includes the enclosure, cables, power supply, etc... I actually cut my teeth on Python learning GNURadio.
- laobeylu 10y ago
  That's true, I'll update the USRP price on the website.
laobeylu 10y ago
Hey! I'm Lukas, the guy who made this. Just discovered someone posted it on Hacker News, pretty exciting for me. If you want to ask me any questions or make comments, I'm here and on reddit: https://www.reddit.com/r/electronics/comments/4uic5r/sdr_platform_ive_been_working_on/ https://www.reddit.com/r/electronics/comments/4uic5r/sdr_pla...
- CamperBob2 10y ago
  Very nice work. You're going to be faced with some interesting questions over the next few years, such as "WTF am I doing wasting time in this classroom?"
- jackhack 10y ago
  Just a quick note to say how impressive this project is, and that it was fun to read your detailed writeup. Thanks for sharing, it's inspiring and a neat bit of engineering on a lot of levels. I learn as much from mistakes (usually my own, but sometimes of others) so I'm glad you shared those, too. One question: If you had to start over on this project, what would you do differently? (I am going to guess you would go straight for a six-layer board rather than 4 to simplify layout...)
  - laobeylu 10y ago
    Thanks! Actually, doing 4 layers first really helped me save cost on the first prototypes while still allowing me to verify almost the complete design. But that's a difficult question. I think it's inevitable for some things to slip through like they did (the wrong valued resistors...) and 3 revisions to get it right were not that many. One thing I'd certainly do is starting with the FPGA design early on, so I'd not just blindly pick a part that looked suitable like I did this time. That would have also eliminated the mistake where I didn't route clocks to clock capable pins.
- xemdetia 10y ago
  Just a technical writing tip, when you are using any sort of acronym that's the subject of the piece it's helpful to do something like SDR (Software Defined Radio), then use SDR through the rest of the text. Either that or do the blog-style hyperlink the first acronym to the wikipedia page or give a footnote.
  - laobeylu 10y ago
    Thanks -- you're right. I've added a link and spelled it out completely in the first sentence now.
Filter 10y ago
SDR: Software-defined radio
btashton 10y ago
Lukas, your schematic link seems to be broken on the project site. I have been thinking about doing a similar project with this chipset actually. I really want to put down about or 8 of these ADI parts and actually make lower cost phased array development environment. One day....
- laobeylu 10y ago
  That'd be a cool project... The link is working for me, the schematics should be here: https://s3.amazonaws.com/freesrp/prototype-r2/freesrp-sch.pdf https://s3.amazonaws.com/freesrp/prototype-r2/freesrp-sch.pd... Are you sure it's broken?
  - DanBC 10y ago
    Your link here, and the link in the article, both work for me. This is a really nice write up of an impressive project!
asimuvPR 10y ago
Amazing project! 1. What are your plans for it? Aside from high altitude balloons. 2. Do you plan to turn this into a sort of "shield" add on? 3. What will you work on after this project is done?
- laobeylu 10y ago
  Thanks! Well, I'm currently working on a new version that I'm hoping to sell. I also still need to work on the software. This won't be an addon, but the next revision will include an expansion header so you can add addons. Should be pretty neat to make an LCD+battery pack "shield" so you can use the SDR as a stand-alone spectrum analyzer. What I'll actually use it for: I built it because I wanted to learn more about signal processing and the different protocols that common devices use, so I'll be tinkering with all those protocols. No idea what I'll do after this, maybe that LCD addon I was talking about?
  - dbyte 10y ago
    Really an amazing job. Keep feeding your curiosity, it is really worth it and try to travel a bit while explaining your project. Array processing is something that deserves a better look. Many SDR solutions still lack a bit under this point of view. Yet that will be quite useful to have. :)
  - asimuvPR 10y ago
    You should get yourself a nice dish antenna. They are cheap and allow for a lot of fun projects. I sourced a free 10-foot dish with motor (to adjust angle) not long ago. Its gonna be used as a backyard radio telescope of sorts. :)
jaytaylor 10y ago
I am curious; what would one actually do with this device once it is working? This is a really neat sounding project.
- ericjang 10y ago
  SDR has a lot of applications in infosec, amateur astronomy, and other signal processing science applications. Check out Balint Seeber's talk at DEF CON 21. https://www.youtube.com/watch?v=1bgC3AjCnA4 https://www.youtube.com/watch?v=1bgC3AjCnA4 another talk: http://www.rtl-sdr.com/new-talk-by-balint-seeber-hacking-the-wireless-world-with-sdr/ http://www.rtl-sdr.com/new-talk-by-balint-seeber-hacking-the...
- jackhack 10y ago
  Transmit or receive analog or digital information on just about any frequency : audio/voice (including multichannel), video, GPS, telecommunications, data transmission, synchronization, module configuration, etc. etc. etc. Sky's the limit.
  - kyzyl 10y ago
    > Sky's the limit. Until you get a bigger antenna ;-)
  - superuser2 10y ago
    Isn't the FCC the limit? How much transmitting can you do legally?
- simcop2387 10y ago
  With 56MHz bandwidth, a lot. You could record and analyze most 802.11 connections (typically 20MHz to 40MHz, except for newer AC hardware that can go to 160MHz). You could also record the entire FM band in your area at once, all of it. Same with AM and a lot of other bands. It'd also probably work really well for recording things like fire and police bands, with trunking and being able to determine an entire conversation at a time that normally need 2 or more cheaper SDRs to record the trunk and then the channels. That would normally mean you'd probably miss some channels that are at the other end of what you're listening to. It'd also mean you can monitor the entire bandwidth of many of the ISM bands to determine what some misbehaving device is doing. So many things that I'd love to do with it! I really want one now.
noonespecial 10y ago
I also had done more revisions of the board and spent way more money than I initially planned for... even though in hindsight, having only three revisions for a fully functioning, moderately complex design, with no previous experience working on something like this, probably is not that bad. Are you kidding? That falls into the realm of superhuman. I've seen 20 year veterans blow a 100 grand and get half that far. I think even Woz would do a double-take.
- bsder 10y ago
  > Are you kidding? That falls into the realm of superhuman. I've seen 20 year veterans blow a 100 grand and get half that far. I think even Woz would do a double-take. A high density BGA through an OSH Park board with a homebrew reflow oven and only 3 revs and a stainless stencil on only the last pass? Yeah, that's really quite good. You practically can't avoid making a mistake on a PCB of that complexity. There are simply too many details buried on too many datasheets and one of them is going to drop. If you have the time, the best thing I have found for catching mistakes is to have a design review. Even if the person doesn't understand electronics, the fact that you have to walk through every part and explain it to somebody means that you will catch some really stupid things. However, if you're good and the board isn't too expensive, it's often cheaper just to fab the board. You're time is worth something, and you can be designing something else while the PCB is being fabbed.
  - laobeylu 10y ago
    That's actually sort of what I did. I didn't explain it to someone else, but went through it in my head, talking to myself explaining the design. Explaining it to someone else must be even better!
    - noonespecial 10y ago
      Or just a rubber duck. https://en.wikipedia.org/wiki/Rubber_duck_debugging https://en.wikipedia.org/wiki/Rubber_duck_debugging Personally I use a cat. Its Steve-Jobs-like attitude seems ideally suited for the task.
mschuster91 10y ago
Could this project, in theory, be done with a 2-layer (front and back) board? I'm thinking of building a small SoC board... but I don't want to shell out hundreds of bucks (and days of shipping time) for prototype PCBs, but hand-etch them instead.
- kersny 10y ago
  Its been done, but AFAIK not with hand etching: http://hforsten.com/making-embedded-linux-computer.html http://hforsten.com/making-embedded-linux-computer.html I don't think you can do high frequency RAM lines with hand etched boards or BGA escape routing without vias, but two layer prototype boards are pretty cheap these days.
mahmoodadv 10y ago
Wow its amazing i like it http://greenlahore.blogspot.com/ http://greenlahore.blogspot.com/
enesunal 10y ago
Is it the truth, or just pure genius? I choose second! What an amazing job, well done!
xt00 10y ago
Awesome project man. I do EE HW design for a living and this I can attest is a hard project. I have a bladeRF and use it regularly. One thing I try to instill in the people that work on my team is that the best attribute you can have and try to foster in your career is not giving up on hard things. So it's great that that is something you have.. To stick with this project for a long time and putting in the time to make it happen. MIT will be a challenge but I'm sure if you stick with it you will end up doing great. Go for something tough and glad you are coming to the US. I have to apologize for politicians that say we don't like foreigners. We do like foreigners and we need them. You will be a great addition to the many awesome people coming here to find there path to great success!

283 points by dominicgs 10y ago

This is a really impressive project, and I am all the more in awe that this guy is only 18 years old. The project is on Github: https://github.com/FreeSRP https://github.com/FreeSRP Reddit discussion: https://www.reddit.com/r/electronics/comments/4uic5r/sdr_platform_ive_been_working_on/ https://www.reddit.com/r/electronics/comments/4uic5r/sdr_pla... He's selling a small batch of these for $350 apiece - calling it now, he's going to be very successful in his career.

laobeylu 10y ago
Thank you for the kind comment. Not selling them yet, though, and the small batch might end up being a little more expensive than that (but I'm really trying to keep it under $400).

batbomb 10y ago

I think the USRP1 motherboard, when I originally used one in 2008, used to be $700 complete/$550 for the motherboard. The price now is $719, but that includes the enclosure, cables, power supply, etc... I actually cut my teeth on Python learning GNURadio.

laobeylu 10y ago
That's true, I'll update the USRP price on the website.

laobeylu 10y ago

Hey! I'm Lukas, the guy who made this. Just discovered someone posted it on Hacker News, pretty exciting for me. If you want to ask me any questions or make comments, I'm here and on reddit: https://www.reddit.com/r/electronics/comments/4uic5r/sdr_platform_ive_been_working_on/ https://www.reddit.com/r/electronics/comments/4uic5r/sdr_pla...

CamperBob2 10y ago
Very nice work. You're going to be faced with some interesting questions over the next few years, such as "WTF am I doing wasting time in this classroom?"
jackhack 10y ago
Just a quick note to say how impressive this project is, and that it was fun to read your detailed writeup. Thanks for sharing, it's inspiring and a neat bit of engineering on a lot of levels. I learn as much from mistakes (usually my own, but sometimes of others) so I'm glad you shared those, too. One question: If you had to start over on this project, what would you do differently? (I am going to guess you would go straight for a six-layer board rather than 4 to simplify layout...)
- laobeylu 10y ago
  Thanks! Actually, doing 4 layers first really helped me save cost on the first prototypes while still allowing me to verify almost the complete design. But that's a difficult question. I think it's inevitable for some things to slip through like they did (the wrong valued resistors...) and 3 revisions to get it right were not that many. One thing I'd certainly do is starting with the FPGA design early on, so I'd not just blindly pick a part that looked suitable like I did this time. That would have also eliminated the mistake where I didn't route clocks to clock capable pins.
xemdetia 10y ago
Just a technical writing tip, when you are using any sort of acronym that's the subject of the piece it's helpful to do something like SDR (Software Defined Radio), then use SDR through the rest of the text. Either that or do the blog-style hyperlink the first acronym to the wikipedia page or give a footnote.
- laobeylu 10y ago
  Thanks -- you're right. I've added a link and spelled it out completely in the first sentence now.

Filter 10y ago

SDR: Software-defined radio

btashton 10y ago

Lukas, your schematic link seems to be broken on the project site. I have been thinking about doing a similar project with this chipset actually. I really want to put down about or 8 of these ADI parts and actually make lower cost phased array development environment. One day....

laobeylu 10y ago
That'd be a cool project... The link is working for me, the schematics should be here: https://s3.amazonaws.com/freesrp/prototype-r2/freesrp-sch.pdf https://s3.amazonaws.com/freesrp/prototype-r2/freesrp-sch.pd... Are you sure it's broken?
- DanBC 10y ago
  Your link here, and the link in the article, both work for me. This is a really nice write up of an impressive project!

asimuvPR 10y ago

Amazing project! 1. What are your plans for it? Aside from high altitude balloons. 2. Do you plan to turn this into a sort of "shield" add on? 3. What will you work on after this project is done?

laobeylu 10y ago
Thanks! Well, I'm currently working on a new version that I'm hoping to sell. I also still need to work on the software. This won't be an addon, but the next revision will include an expansion header so you can add addons. Should be pretty neat to make an LCD+battery pack "shield" so you can use the SDR as a stand-alone spectrum analyzer. What I'll actually use it for: I built it because I wanted to learn more about signal processing and the different protocols that common devices use, so I'll be tinkering with all those protocols. No idea what I'll do after this, maybe that LCD addon I was talking about?
- dbyte 10y ago
  Really an amazing job. Keep feeding your curiosity, it is really worth it and try to travel a bit while explaining your project. Array processing is something that deserves a better look. Many SDR solutions still lack a bit under this point of view. Yet that will be quite useful to have. :)
- asimuvPR 10y ago
  You should get yourself a nice dish antenna. They are cheap and allow for a lot of fun projects. I sourced a free 10-foot dish with motor (to adjust angle) not long ago. Its gonna be used as a backyard radio telescope of sorts. :)

jaytaylor 10y ago

I am curious; what would one actually do with this device once it is working? This is a really neat sounding project.

ericjang 10y ago
SDR has a lot of applications in infosec, amateur astronomy, and other signal processing science applications. Check out Balint Seeber's talk at DEF CON 21. https://www.youtube.com/watch?v=1bgC3AjCnA4 https://www.youtube.com/watch?v=1bgC3AjCnA4 another talk: http://www.rtl-sdr.com/new-talk-by-balint-seeber-hacking-the-wireless-world-with-sdr/ http://www.rtl-sdr.com/new-talk-by-balint-seeber-hacking-the...
jackhack 10y ago
Transmit or receive analog or digital information on just about any frequency : audio/voice (including multichannel), video, GPS, telecommunications, data transmission, synchronization, module configuration, etc. etc. etc. Sky's the limit.
- kyzyl 10y ago
  > Sky's the limit. Until you get a bigger antenna ;-)
- superuser2 10y ago
  Isn't the FCC the limit? How much transmitting can you do legally?
simcop2387 10y ago
With 56MHz bandwidth, a lot. You could record and analyze most 802.11 connections (typically 20MHz to 40MHz, except for newer AC hardware that can go to 160MHz). You could also record the entire FM band in your area at once, all of it. Same with AM and a lot of other bands. It'd also probably work really well for recording things like fire and police bands, with trunking and being able to determine an entire conversation at a time that normally need 2 or more cheaper SDRs to record the trunk and then the channels. That would normally mean you'd probably miss some channels that are at the other end of what you're listening to. It'd also mean you can monitor the entire bandwidth of many of the ISM bands to determine what some misbehaving device is doing. So many things that I'd love to do with it! I really want one now.

noonespecial 10y ago

I also had done more revisions of the board and spent way more money than I initially planned for... even though in hindsight, having only three revisions for a fully functioning, moderately complex design, with no previous experience working on something like this, probably is not that bad. Are you kidding? That falls into the realm of superhuman. I've seen 20 year veterans blow a 100 grand and get half that far. I think even Woz would do a double-take.

bsder 10y ago
> Are you kidding? That falls into the realm of superhuman. I've seen 20 year veterans blow a 100 grand and get half that far. I think even Woz would do a double-take. A high density BGA through an OSH Park board with a homebrew reflow oven and only 3 revs and a stainless stencil on only the last pass? Yeah, that's really quite good. You practically can't avoid making a mistake on a PCB of that complexity. There are simply too many details buried on too many datasheets and one of them is going to drop. If you have the time, the best thing I have found for catching mistakes is to have a design review. Even if the person doesn't understand electronics, the fact that you have to walk through every part and explain it to somebody means that you will catch some really stupid things. However, if you're good and the board isn't too expensive, it's often cheaper just to fab the board. You're time is worth something, and you can be designing something else while the PCB is being fabbed.
- laobeylu 10y ago
  That's actually sort of what I did. I didn't explain it to someone else, but went through it in my head, talking to myself explaining the design. Explaining it to someone else must be even better!
  - noonespecial 10y ago
    Or just a rubber duck. https://en.wikipedia.org/wiki/Rubber_duck_debugging https://en.wikipedia.org/wiki/Rubber_duck_debugging Personally I use a cat. Its Steve-Jobs-like attitude seems ideally suited for the task.

mschuster91 10y ago

Could this project, in theory, be done with a 2-layer (front and back) board? I'm thinking of building a small SoC board... but I don't want to shell out hundreds of bucks (and days of shipping time) for prototype PCBs, but hand-etch them instead.

kersny 10y ago
Its been done, but AFAIK not with hand etching: http://hforsten.com/making-embedded-linux-computer.html http://hforsten.com/making-embedded-linux-computer.html I don't think you can do high frequency RAM lines with hand etched boards or BGA escape routing without vias, but two layer prototype boards are pretty cheap these days.

mahmoodadv 10y ago

Wow its amazing i like it http://greenlahore.blogspot.com/ http://greenlahore.blogspot.com/

enesunal 10y ago

Is it the truth, or just pure genius? I choose second! What an amazing job, well done!

xt00 10y ago

Awesome project man. I do EE HW design for a living and this I can attest is a hard project. I have a bladeRF and use it regularly. One thing I try to instill in the people that work on my team is that the best attribute you can have and try to foster in your career is not giving up on hard things. So it's great that that is something you have.. To stick with this project for a long time and putting in the time to make it happen. MIT will be a challenge but I'm sure if you stick with it you will end up doing great. Go for something tough and glad you are coming to the US. I have to apologize for politicians that say we don't like foreigners. We do like foreigners and we need them. You will be a great addition to the many awesome people coming here to find there path to great success!