SM2000 – Part 8 – Gippstech 2016 Presentation

Justin, VK7TW, has published a video of my SM2000 presentation at Gippstech, which was held in July 2016.

Brady O’Brien, KC9TPA, visited me in June. Together we brought the SM2000 up to the point where it is decoding FreeDV 2400A waveforms at 10.7MHz IF, which we demonstrate in this video. I’m currently busy with another project but will get back to the SM2000 (and other FreeDV projects) later this year.

Thanks Justin and Brady!

FreeDV and this video was also mentioned on this interesting Reddit post/debate from Gary KN4AQ on VHF/UHF Digital Voice – a peek into the future

4 thoughts on “SM2000 – Part 8 – Gippstech 2016 Presentation”

  1. In playing with 2400A I notice that it always gets the first two bits wrong. 94 out of 96 ain’t bad :-) So, I’m thinking I’m going to add a little preamble on there (96-bits). Maybe some polynomial that tracks fast.

    1312.500 F1
    2390.625 F2
    3609.375 F3
    4781.250 F4
    xx-1011101000100001111011101010100011010110110111000111100101101010001010101001000010011000001011-11
    10-1011101000100001111011101010100011010110110111000111100101101010001010101001000010011000001011-xx
    SNR = 16.40

    1. I use 2400B with standard FM sets, like in the good old packet days you need to account for ‘tx-delay’ (time between activating the PTT line and the transmitter actually having a proper carrier in air).
      I fill that time with data frames. If you have set your address (callsign) and send empty data frames you basicly get a preamble consisting of your callsign. If the other side happens to successfully decode it early they already know who you are.

      (Code can be found at http://video.vreeken.net/~pe1rxq/eth_ar.git/)

    2. Hi Coupe,

      Can you provide a test case that causes the leading bit errors in fsk_demod against the current code in the freetel-code svn repo?

      1. I’ll have to write a program, as what I’m doing is modulating 48 random dibits then demodulating that small spectrum. I don’t think there’s anything in the svn for that.

        This whole test may be bogus as these short groups of random dibits seem to create a spectrum that the fft has trouble with since there’s not a lot of samples. (I’ve created garbage, ha)

        That is, a normal framed conversation would be much easier to demodulate error-free.

        https://github.com/a-la-mode/FSKModem

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