sBitx and HF SDR

Reflecting on the last time I was interested in radio, and at that time I was listening tot he Soldresmoke podcast. 2 things stuck out for me from that podcast, the talk of “Experimental Methods in RF Design”, Wes Hayward et al and some dude in India who had created a low cost radio based on easily accessible parts from a television, the BITX20 built by Ashhar Farhan. So after a little bit of searching I cam across the fact that the old BITX20 had grown to be the sBITX SDR radio.

• https://soldersmoke.blogspot.com/search/label/sBITX
  • which links to Dean’s KK4DAS site where he homebrewed his own sBITX https://kk4das.blogspot.com/2024/02/homebrew-sbitx-receiver-gound-bounce.html with some discussion of the build

searching deeper on Soldersmoke, I found https://soldersmoke.blogspot.com/2021/05 which has a video that goes back to the source and Farham himself talking about his inspirations for the sBITX

Ashhar Farhan “sBITX - An Open-Source SDR the YOU Can Hack!” FDIM 2021 - FDIM Archives

in this phenomenal video, Farhan, spells out the game changer that microcontrollers are to modern electronics and HAM radio builds. I love his embrace of the OpenSource, hackable ethos and accepting changes and advances in technology whilst still keeping to a true, amateur build in a back yard shed.

In the video he mentions the evolution of microcontrollers controlling radios, starting with a Raspberry Pi Pico

uSDR-Pico: Homemade SDR-Transceiver with Raspberry Pi Pico - juthoff62

running

• https://github.com/ArjanteMarvelde/uSDR-pico (last updated 2 years ago)
• expanded on here https://github.com/kaefe64/Arduino_uSDX_Pico_FFT_Proj (last updated 2 months ago)

uSDR-Pico with FFT/Waterfall on TFT Display - Klaus F - PY2KLA

uSDR-Pico with FFT/Waterfall on TFT Display + Visual Scope - Klaus F PY2KLA

and from RasPi pico moving onto the Teensy

A Teensy based SDR is described here https://www.pjrc.com/convolution-software-defined-radio/

• https://github.com/DD4WH/Teensy-ConvolutionSDR/tree/master
  • https://www.janbob.com/electron/SDR_Ctrl1/SDR_Ctrl1.html
    • also intersting circuits on this page W7PUA like a noise generator - https://www.janbob.com/electron/Noise/NoiseGen1.htm

a next step might be moving onto a RasPi with a PiHat like Radioberry? SDR Radioberry V2.0 b4 for RPi 4-Wireless Card Analog Device AD986 Supports the 10CL25

but in this case the answer is the sBitx SDR from Farhan.

https://www.sbitx.net/

there is also intresting comment here about using the WM8731 Wolfsom Audio CODEC chip with inbuilt Headphone Driver

• available as a pre built board https://www.aliexpress.com/item/1005004007148615.html

He seems to mention “the paper” a number of times, and also refers to his github

• https://github.com/afarhan
• the paper from the YouTube description https://tinyurl.com/5xn7v22a and here for posterity

  • sBITX – An open source SDR that you can hack - By Ashhar Farhan, VU2ESE

    sbitx_v4.pdf

I am yet to listen in more detail to: crystal filter, thermal noise, FFT, Specturm display, convolutional filtering

Skipping to the end I found a bunch of interesting references

• A Software-Defined Radio for the Masses part 1-4 via https://www.arrl.org/
  1. A Software-Defined Radio for the Masses part 1
  2. A Software-Defined Radio for the Masses part 2
  3. A Software-Defined Radio for the Masses part 3
  4. A Software-Defined Radio for the Masses part 4
• The Scientist and Engineer’s Guide to Digital Signal Processing By Steven W. Smith, Ph.D. - https://dspguide.com/ available free online - pdf per chapter
• Experimental Methods in RF Design (with CD) is also a great resource for Digital Methods EMRFD
• finally a lot of the C code was written by Phil Karn, KA9Q
  • the quoted page http://www.ka9q.net/ka9q-radio.tar.xz
  • via https://web.archive.org/web/20220408114116/http://www.ka9q.net/ka9q-radio.tar.xz
    • ka9q-radio.tar.xz