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Date: Sat, 23 Jan 2016 19:13:38 +0100
From: IZ7SLZ <iz7slz.domenico@gmail.com>
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Subject: Re: VLF: Software PSK modulation
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Hello Markus,

many thanks for sharing details of your very interesting experiment. As 
you known,  i have used your PLL method in my LF-EbNaut setup to 
generate a quite steady  modulating audio tone. But in my case, the 
feedback is taken at the output of the sound card before the 
ring-modulator that acts the bpsk.
If i have understood, you have now overcome the initial problem of this 
PLL that tends to cancels the psk modulation. That's good. I will try it 
in my next VLF local transmissions.

Since two days, i'm running a (temporarily !) VLF receiver/grabber with 
a resolution of 63 uHz:

https://www.dropbox.com/s/fsjkfuhggozzv5w/grabber.jpg?dl=0

Unfortunatly no signals on "dreamer" band in these two days of activity 
(made by you and Uwe)  was picked up. I'm working to improve reception 
trying to relocate the mini-whip. Next step will be to test a Loop 
antenna. By the way, the chances to pick up a VLF "dreamer" signal from 
Central Europe are very less here in my station in JN80 that is 
"urban-located" and fairly far from you.

I want to try to record and decode my local EbNaut signals on VLF. I 
made some reception test using Wolf's beta version that includes EbNaut 
facilities. I have succesfully tested it on MF during some test 
transmissions of IW4DXW. But i want test also your recording method that 
uses the FFT export file function of Spectrum Lab.
Taking in consideration that i'm using 48000 sample/s can you suggest 
the correct parameters needed for SL and for the sr.txt file used for 
the inverse-FFT program ?

Maybe someone else is interested at this method.

Thanks in advance.

73 and good week-end to all group

Domenico / iz7slz


On 1/23/2016 4:52 PM, Markus Vester wrote:
> For yesterday's EbNaut transmission, I have not employed the usual 
> Rubidium oscillator and automatic antenna variometer hardware, but 
> reverted to the software modulation scheme which had been originally 
> used for our first tests in April 2014. This is an extension of the 
> "green line" anti-glitch method, with 1pps-sync in SpecLab and RF 
> feedback of the analog output to the ADC input. To generate PSK 
> modulation, the phase prescription for the software PLL is no longer 
> fixed at 180° (green in the colour spectrogram), but switched between 
> 90° (red) and 270° (sky-blue) by a SpecLab script which periodically 
> reads 1 or 0 symbols from a text file.
> The primary advantage of this method is that no external hardware 
> modulator is needed. With the feedback picked up from the antenna, it 
> also intrinsically compensates for wind-induced resonance variations 
> and can do without an automatic variometer. Thirdly, the phase 
> switching occurs smoothly by frequency variation, reducing switching 
> transients and far-away sidebands. The main disadvantage is that the 
> phase ramping takes time (about 1 to 3 seconds) and also introduces 
> some jitter, so this method cannot be used effectively for fast 
> signaling with symbols shorter than 5 seconds.
> If you would like to try, a SpecLab configuration file can be found at
> http://df6nm.bplaced.net/VLF/_vlf_tx_pll_psk.USR
> To use it, you first need to set up GPS 1pps and audio feedback as 
> described in
> http://df6nm.bplaced.net/VLF/VLF_Transmit_phase_correction.txt
> This can be done either with a stereo input soundcard (1pps on the 
> right, RF feedback on the left channel), or mono with both signals 
> combined through resistors (RF feedback about 5% of the 1 pps level). 
> Make sure that the 1pps samplerate detector is locking properly (i.e. 
> mostly green), and your PC time is close to the nearest second.
> Then you need to encode your message using Paul's ebnaut-tx software
> http://abelian.org/ebnaut/
> and press "Save" to make a text file. For use with the SpecLab script, 
> you then need to insert spaces as separators between the 0 and 1 
> digits, e.g. converting "1001..." into " 1 0 0 1..." by replacing 0s 
> and 1s in notepad (note that "1 0 0 1 ..." works just as well but may 
> produce a surprising result when reopening the file - search for "bush 
> hid the facts" ;-) As an example, my recent transmission is at
> http://df6nm.bplaced.net/VLF/psk_8k19a_73.txt
> The file should be saved as psk.txt and placed in your SpecLab home 
> directory.
> Then you will want to select
> - the TX frequency in the second oscillator of the test signal generator,
> - the symbol duration as periodic actions interval (eg. 10 seconds),
> - the start time, by letting scheduled actions open psk.txt a couple 
> of seconds before. You should also close the file after the transmission,
> - and finally tick "send unmodulated test tone at TX frequency" in the 
> digimode terminal to let the signal appear on the left output.
> A couple of notes regarding frequency selection: For straight carrier 
> experiments, staying within very few mHz of 8270 Hz can show the 
> signal on various grabbers. However EbNaut PSK reception would be 
> susceptible to co-channel interference over a wider bandwidth, eg. +- 
> 0.1 Hz for 10 second symbols. As the PSK signal will anyway be 
> invisible on the grabbers, it might be advisable to choose e.g. 8970.1 
> or 8969.9 Hz for future PSK transmissions, thereby nulling potential 
> carriers near 8270.000 but still staying inside the decimated IQ 
> bandwidth for EbNaut recordings (+-0.25 Hz here).
> As SpecLab aligns the absolute phase to time-of-day, the TX frequency 
> for overnight transmissions should be a multiple of 1/86400 Hz to 
> avoid an Alpha-like midnight phase step.
> Hope this may help to get a few more EbNaut signals on air... Big 
> thanks to Paul and Wolf for making all this possible.
> All the best,
> Markus (DF6NM)


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    <div class="moz-cite-prefix">Hello Markus,<br>
      <br>
      many thanks for sharing details of your very interesting
      experiment. As you known,  i have used your PLL method in my
      LF-EbNaut setup to generate a quite steady  modulating audio tone.
      But in my case, the feedback is taken at the output of the sound
      card before the ring-modulator that acts the bpsk.<br>
      If i have understood, you have now overcome the initial problem of
      this PLL that tends to cancels the psk modulation. That's good. I
      will try it in my next VLF local transmissions.<br>
      <br>
      Since two days, i'm running a (temporarily !) VLF receiver/grabber
      with a resolution of 63 uHz:<br>
      <br>
      <a class="moz-txt-link-freetext" href="https://www.dropbox.com/s/fsjkfuhggozzv5w/grabber.jpg?dl=0">https://www.dropbox.com/s/fsjkfuhggozzv5w/grabber.jpg?dl=0</a><br>
      <br>
      Unfortunatly no signals on "dreamer" band in these two days of
      activity (made by you and Uwe)  was picked up. I'm working to
      improve reception trying to relocate the mini-whip. Next step will
      be to test a Loop antenna. By the way, the chances to pick up a
      VLF "dreamer" signal from Central Europe are very less here in my
      station in JN80 that is "urban-located" and fairly far from you.<br>
      <br>
      I want to try to record and decode my local EbNaut signals on VLF.
      I made some reception test using Wolf's beta version that includes
      EbNaut facilities. I have succesfully tested it on MF during some
      test transmissions of IW4DXW. But i want test also your recording
      method that uses the FFT export file function of Spectrum Lab.<br>
      Taking in consideration that i'm using 48000 sample/s can you
      suggest the correct parameters needed for SL and for the sr.txt
      file used for the inverse-FFT program ?<br>
      <br>
      Maybe someone else is interested at this method.<br>
      <br>
      Thanks in advance.<br>
      <br>
      73 and good week-end to all group<br>
      <br>
      Domenico / iz7slz<br>
      <br>
      <br>
       <br>
      <br>
       <br>
      <br>
       <br>
      <br>
      <br>
      On 1/23/2016 4:52 PM, Markus Vester wrote:<br>
    </div>
    <blockquote
      cite="mid:8D3240D41785ED1-1038-6435BD@webmail-vm010.sysops.aol.com"
      type="cite">
      <div style="color: black; font-family: arial; font-size: 10pt;"><span
          style="display: inline-block;" contenteditable="false"></span></div>
      <div>For yesterday's EbNaut transmission, I have not employed the
        usual Rubidium oscillator and automatic antenna variometer
        hardware, but reverted to the software modulation scheme which
        had been originally used for our first tests in April 2014. This
        is an extension of the "green line" anti-glitch method, with
        1pps-sync in SpecLab and RF feedback of the analog output to the
        ADC input. To generate PSK modulation, the phase prescription
        for the software PLL is no longer fixed at 180° (green in the
        colour spectrogram), but switched between 90° (red) and 270°
        (sky-blue) by a SpecLab script which periodically reads 1 or 0
        symbols from a text file.</div>
      <div> </div>
      <div>The primary advantage of this method is that no external
        hardware modulator is needed. With the feedback picked up from
        the antenna, it also intrinsically compensates for wind-induced
        resonance variations and can do without an automatic variometer.
        Thirdly, the phase switching occurs smoothly by frequency
        variation, reducing switching transients and far-away sidebands.
        The main disadvantage is that the phase ramping takes time
        (about 1 to 3 seconds) and also introduces some jitter, so this
        method cannot be used effectively for fast signaling with
        symbols shorter than 5 seconds.   </div>
      <div> </div>
      <div>If you would like to try, a SpecLab configuration file can be
        found at<br>
        <a moz-do-not-send="true"
          href="http://df6nm.bplaced.net/VLF/_vlf_tx_pll_psk.USR">http://df6nm.bplaced.net/VLF/_vlf_tx_pll_psk.USR</a></div>
      <div> </div>
      <div>To use it, you first need to set up GPS 1pps and audio
        feedback as described in <br>
        <a moz-do-not-send="true"
          href="http://df6nm.bplaced.net/VLF/VLF_Transmit_phase_correction.txt">http://df6nm.bplaced.net/VLF/VLF_Transmit_phase_correction.txt</a><br>
        This can be done either with a stereo input soundcard (1pps on
        the right, RF feedback on the left channel), or mono with both
        signals combined through resistors (RF feedback about 5% of the
        1 pps level). Make sure that the 1pps samplerate detector is
        locking properly (i.e. mostly green), and your PC time is close
        to the nearest second. </div>
      <div> </div>
      <div>Then you need to encode your message using Paul's ebnaut-tx
        software<br>
        <a moz-do-not-send="true" href="http://abelian.org/ebnaut/">http://abelian.org/ebnaut/</a><br>
        and press "Save" to make a text file. For use with the SpecLab
        script, you then need to insert spaces as separators between the
        0 and 1 digits, e.g. converting "1001..." into " 1 0 0 1..." by
        replacing 0s and 1s in notepad (note that "1 0 0 1 ..." works
        just as well but may produce a surprising result when reopening
        the file - search for "bush hid the facts" ;-) As an example, my
        recent transmission is at<br>
        <a moz-do-not-send="true"
          href="http://df6nm.bplaced.net/VLF/psk_8k19a_73.txt">http://df6nm.bplaced.net/VLF/psk_8k19a_73.txt</a><br>
        The file should be saved as psk.txt and placed in your SpecLab
        home directory. </div>
      <div> </div>
      <div>Then you will want to select<br>
        - the TX frequency in the second oscillator of the test signal
        generator,<br>
        - the symbol duration as periodic actions interval (eg. 10
        seconds),<br>
        - the start time, by letting scheduled actions open psk.txt a
        couple of seconds before. You should also close the file after
        the transmission, <br>
        - and finally tick "send unmodulated test tone at TX frequency"
        in the digimode terminal to let the signal appear on the left
        output.</div>
      <div> </div>
      <div>A couple of notes regarding frequency selection: For straight
        carrier experiments, staying within very few mHz of 8270 Hz can
        show the signal on various grabbers. However EbNaut PSK
        reception would be susceptible to co-channel interference over a
        wider bandwidth, eg. +- 0.1 Hz for 10 second symbols. As the PSK
        signal will anyway be invisible on the grabbers, it might be
        advisable to choose e.g. 8970.1 or 8969.9 Hz for future PSK
        transmissions, thereby nulling potential carriers near 8270.000
        but still staying inside the decimated IQ bandwidth for EbNaut
        recordings (+-0.25 Hz here). </div>
      <div> </div>
      <div>As SpecLab aligns the absolute phase to time-of-day, the TX
        frequency for overnight transmissions should be a multiple of
        1/86400 Hz to avoid an Alpha-like midnight phase step.</div>
      <div> </div>
      <div>Hope this may help to get a few more EbNaut signals on air...
        Big thanks to Paul and Wolf for making all this possible. </div>
      <div> </div>
      <div>All the best, <br>
        Markus (DF6NM)</div>
      <div> </div>
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