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teensy sdr transceiver – part 1

I’ve been following along with ZL2CTM’s latest Teensy SDR transceiver build and I’ve been trying to emulate his design even down to his construction style with the strip board. So far, I’ve got the radio receiving well enough. After troubleshooting a bad grinding and squealing noise for a week, I found a bad audio transformer. After replacing that, the rig came to life.

I was able to generate the quadrature oscillators with the SI5351 as detailed in this post and I’m amplifying the audio with the teensy itself, rather than an external audio amp. I’ll probably change that soon as it is still fairly low output and doesn’t sound that great. There is a video below demonstrating reception, but the audio is kind of low.

I’ve got some bad tuning clicks that I’ll need to resolve, but I’m happy with the progress so far. I would definitely recommend subscribing to Charlie’s Youtube channel. His videos are great and I have learned a lot from them.






Below is my code so far. I started with Charlie’s code and modified it to suit my needs.



    • awsh awsh

      Thanks for the links Charlie. I’ve been away for a bit, so I hadn’t seen those yet.

      I’ve done some testing with an adafruit breakout board and I don’t think it will make it down below about 4.7MHz with the quadrature outputs since it uses a 25MHz reference oscillator. Hans is using a 27MHz oscillator with his QCX and in the PDF you linked, he states:

      with a 27MHz reference oscillator crystal, the lowest frequency at which the Si5351A configuration supports quadrature LO on two outputs, is 3.2MHz.

      I’ve been searching through the junk box for a 27MHz crystal so I can test that, but no luck so far.

      I’ll definitely let you know if I get it working.

      • Charles T Morris Charles T Morris

        That very interesting thanks. Hopefully, between the two of us we can nut it out!

        Charlie, ZL2CTM

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