Meteor M-N2 Images

Friday, 18 May 2018

Homebrew SDR HF Transceiver - decision time

The video below shows my Homebrew SDR rx working with the GUI on the STM32F746-Discovery board.


However, what you might notice is the presence of image products in the waterfall. The processing of the signal suppresses all but the very strongest of these so they don't appear as audio but it is mighty confusing when they are on the waterfall but actually not there (if you see what I mean)!

I am in the process of building a QSD or Tayloe Detector, which should provide better rejection of images. I have breadboarded one of these, it works but not very well. I think that this might be due to the length of leads I have on the breadboard so I am trying to use Eagle CAD to design a circuit board to overcome these problems.


4 comments:

  1. Hi, this is Chin Beckmann, CEO of DSP Concepts which provides Audio Weaver. Looks like you are doing some interesting stuff on your own with Audio Weaver. Would you be interested in getting a more advanced version of Audio Weaver to take you to the next level? Please contact me at cbeckmann@dspconcepts.com.

    ReplyDelete
  2. Hello Simon!

    How did you implemented the SSB demodulator? You mixed the audio from a downconverter with a constant carrier in Audioweaver?
    Thanks,
    Adrian 73 deYO3HJV

    ReplyDelete
    Replies
    1. Hi Adrian,
      Apologies for the late reply. I don't recall seeing a notification that you had added a comment. Anyway, if you look at my previous post you will see the AudioWeaver design, which does use a 11 kHz sine wave to mix with the incoming baseband audio. You don't *need* to mix with a local oscillator as the signal is already at baseband, i.e. audio frequencies, but if you don't the signal is very unclean with mains hum and other nasties. Once the baseband signal is mixed with the 11 kHz LO this means you need to filter the signal with a filter from about 11.3 kHz to about 14 kHz to recover USB or the opposite direction for LSB. However, although this is one approach to the phasing method of SSB demodulation there are other ways.

      I have experimented with several methods, that is the beauty of the AudioWeaver software - it enables rapid prototyping. I haven't yet decided on the approach to carry forward as I have been concentrating on hardware, building a QSD 'Tayloe' detector.

      I hope this answers your question.
      73 Simon.

      Delete
  3. Hello - I was curious if your source code is available on github or else where? I have a STM32F7 Discovery board and I would love to see how you have set up your project.

    I am using Visual Studio Code and PlatoformIO. They support the STM32 using the STM32Cubic framework.

    -Freeman, N5FPP

    ReplyDelete