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Thread: Teensy Software Defined Radio Receiver

  1. #1
    Senior Member DD4WH's Avatar
    Join Date
    Oct 2015
    Central Europe

    Teensy Software Defined Radio Receiver

    For all SDR radio fans who use the excellent Teensy audio library, I would like to present some information that could be of interest for your own projects or for understanding how SDR radio with the Teensy could work.

    Rich VE3MKC has prepared an excellent basis for a Teensy SDR radio (

    My Teensy SDR receiver implementation now has demodulation of LSB, USB, AM, DSB and "pseudo" StereoAM (USB right ear, LSB left ear) with adjustable filter bandwidths and the possibility to record audio from the radio to files on the audio boardīs SD card. This has only been possible with the help of you guys of the PJRC forum, thanks very much!

    I prepared a rather long document to explain the various demodulation and software functions and the audio path and how it works in detail and also a brief description of the hardware:

    The source code is available here:

    (When you look at the code, please be patient, as I am not a programmer and many things can surely be made more effective, elegant etc.)

    I have prepared several videos on Youtube to show you my version, the DD4WH Teensy SDR Receiver and the various menu entries and functions:

    In the hope that this will promote interest in the great Teensy platform for more SDR work, have fun with Richīs SDR experimenting platform!

    73 de Frank DD4WH

  2. #2
    Junior Member
    Join Date
    Jan 2016
    Wonderful build. It would be interesting to know if this could be adapted to use the RTL-SDR ( I think it would be a long while before I could produce anything near as complex as your full build! Thank you for posting your code.
    BW Bill

  3. #3
    Senior Member
    Join Date
    Dec 2014
    All you need for a SDR is a compiler:

  4. #4

    I've been looking at a few of these SDR's based on the Teensy 3.1/2 and would like to build one down the road, DD4WH do you have complete schematics and an exact parts list/source for the radio you built? Also would it be possible to use both a Teensy 3.X for the hard tasks and add a Teensy LC for the other functions like I/O and Display Drive?



  5. #5
    Senior Member
    Join Date
    May 2016
    I am starting to look at AGC for my completely DIY Teensy SDR. I'm looking at the Cute SDR AGC as a prototype. A couple of questions:
    1) What is the status of the software AGC as contained in the Rich VE3MKC original package - there is a comment in there saying it probably no longer works after an update to the Audio library?

    2) Has anybody looked at "gain scheduling" for multiple AGC control points? For example, I currently have three points at which I could apply AGC gain/attenuation:
    - 2 bits of RF attenuation (0, -6, -10, -16 dB) at the antenna terminals.
    - -22.5dB attenuation in 1.5dB steps by controlling the ADC full scale range at the LineInLevel in the Audio board,
    - AF gain/attenuation post demodulation using a mixer.
    and the goal would be to keep the full dynamic range of the ADC active, while maximizing the SNR by mixing and matching gains.
    Note that the first two imply closed-loop "feedback" AGC like the good old superhet receivers of yesteryear where the AGC was applied to the RF & IF stages, while the third is open-loop "feedforward". The analysis is different for the two cases.


  6. #6
    Senior Member DD4WH's Avatar
    Join Date
    Oct 2015
    Central Europe
    @Jim: have a look here:

    There you will find the documentation and the soource code.

    I have no "exact" part list etc., because my Teensy SDR is constantly changing ;-) Now I have the Si514 as a LO working instead of an Si5351, could potentially improve phase noise and eliminate the spurs of the Si5351, but have not yet checked. The whole fun thing with the Teensy SDR is to learn by yourself and build your own unique rig. Rich also has a schematic in his blog and in my documentation you will find my schematic in some detail and detailed explanation, how the software works.

    I have no experience in coupling two Teensys, so I cannot comment on your idea of using a Teensy 3.1 and an additional Teensy LC.

    @Derek: I have not used the software AGC by Rich, because it did not work in my setup. The simple hardware AGC that Rich implemented uses the codecīs built-in AGC and works, but I am not a particular fan of AGC anyway, so I do not use AGC at the moment with the Teensy SDR. You could have a look at the software in the mcHF SDR! There Clint KA7OEI has built a very good AGC that works extremely good. Not easily implemented however . . .

    I would be very interested in your AGC approach when you manage to finish it! Your plan sounds good, however I would concentrate on software AGC in order to keep hardware to a minimum, but your mileage may vary!

    Have fun & good luck,

    73 de Frank DD4WH

  7. #7
    Junior Member
    Join Date
    Mar 2017
    Sherwood, OR

    Teensy SDR

    Here is my build of the Teensy SDR.

    When first built I was running VE3MKC firmware, but have now upgraded to DD4WH. I am using a Softrock II lite for the QSD and RF front end so I am currently limited to just one band (40m). I did pick up a few LPFs from QRP Labs (40m, 20m, 10m) and am going to make a switchable front end for it where the lipo battery is shown in the pics. I didn't end up installing the internal battery and have just been running it mobile off of a USB battery jump pack.

    I did add USB audio to the project. Super simple, only 3 lines of code and a setting change in the arduino environment and tada, USB Audio! I can now use FLdigi to decode CW via the USB Audio Interface, while I still have the headphones in. The volume knob changes the headphone volume, but not the USB audio, which I find very convenient.

    Next on my TODO list is a CAT interface (hamlib), and possibly a CW decoder.

    Current BOM cost is about $105 USD.
    Here is the parts list I used for reference:

    Part qty Price Where
    1.8 SPI TFT 128x160 ST7735R 1 $7.49 Amazon
    Rotary Encoder 1 $1.22 ebay
    Buttons 6 $3.00
    Enclosure 80x50x20 Silver 1 $4.99 ebay
    Teensy 3.2 1 $24.99 Amazon
    Teensy Audio Sheild 1 $21.84 Amazon
    SoftRock Lite II (40m) 1 $24.17 FiveDash
    Potentiometer 10k 1 $3.00
    PCB, Main (double clad) 1 $1.00 ebay
    PCB, Controls (proto board) 1 $1.00 ?
    PCB, Teensy Breakout 1 $2.14 OSH Park
    BNC, Flange Mount 1 $3.00 ebay
    Adafruit ID:2045 Freq Gen (Si5351A) 1 $7.95 Adafruit

    Just wanted to show off my build, and say thanks for all the hard work. I am already starting to collect parts for a Teensy Convolution build.

  8. #8
    Junior Member
    Join Date
    Jul 2018
    I should post my question here.
    You are the expert.!

    Ich haette lieber meine Frage hier stellen sollen!
    Sie sind doch Fachmann!

    Last edited by ds1lmp; 07-28-2018 at 07:34 AM.

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