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Date: Sun, 29 Dec 2013 12:18:44 +0100
From: wolf_dl4yhf <dl4yhf@freenet.de>
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Subject: Re: LF: VLF exciter
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Hello Markus,

Ok .. i had assumed the problem was the flipflop (or binary frequency 
divider) which would be in an unpredictable state when not fed with a 
phase-coherent signal "in the gaps" (zeroes in the Opera- or whatever 
amplitude keyed signal).
This could be solved by providing the auxiliary output from the 
soundcard (at 2 * f_tx), to keep the divider chain running.
Depending on the MOSFET gate drivers, it may also be possible to feed 
the 'keying signal' to an output-enable-signal, but I'm not sure if that 
would put the driver output in high-impedance state (which would result 
in a catastrophic 'bang' if both FET gates were left floating).

Anyway your suggestion with the xor gate may be the simpler variant than 
using two different output signals from the soundcard.

73 and HNY,
   Wolf .

(p.s. just managed to build a transformer for a low-voltage MF PA, which 
transforms 0.6 Ohms drain load impedance to 12.5 Ohm with very low stray 
inductance.. using copper foil instead of wire, and thin adhesive tape 
("Tesafilm") as insulator. But that's another story..)


Am 29.12.2013 12:00, schrieb Markus Vester:
> Hi Wolf,
> I think Stefan was only trying to solve the simpler problem of 
> generating a dual squarewave drive for his VLF PA, and was not aiming 
> for amplitude modulated output yet. So when he transmits Opera we'll 
> just have to live with ultra-strong keyclicks, devastating the 9 kHz 
> band all over Europe ;-))
> But I remember that in 2011 we discussed about transmitting 
> high-quality Hell piccies. As you say, the Kahn technique with a 
> separate AM modulator is certainly a good and efficient option. At 
> VLF, outphasing (aka Chireix or LINC technique) between two 
> half-bridges would be a valid alternative. There's some software for 
> the purpose (including Basic source code ;-) on
> df6nm.bplaced.net/VLF/chirppix_outphase.zip 
> <http://df6nm.bplaced.net/VLF/chirppix_outphase.zip>
> This works in conjunction with your SndOutpt audio utility, generating 
> the two outphasing carriers at the left and right stereo output.
> Best 73,
> Markus (DF6NM)
>
> *From:* wolf_dl4yhf <mailto:dl4yhf@freenet.de>
> *Sent:* Sunday, December 29, 2013 9:12 AM
> *To:* rsgb_lf_group@blacksheep.org <mailto:rsgb_lf_group@blacksheep.org>
> *Subject:* Re: LF: VLF exciter
>
> My suggestion:
>
> Use two outputs from the stereo soundcard:
> An "amplitude" and a "phase" channel. The output from the phase 
> channel will be a square wave, coherent, constant amplitude, fed to 
> the divider chain. The "amplitude" channel delivers, well, the 
> amplitude (as a waveform with variable voltage) which, after 
> rectification, drives the final voltage via an additional mosfet. I 
> think the software option is already there, and iirc it has been used 
> (by Jim ?) for an LF PA.
> This way, you could even use amplitude shaping if the bandwidth (from 
> the hard-keyed PA) was a problem - which I don't think it is, on VLF.
>
> Cheers,
>   Wolf
>
>  (p.s. problem with the "very long command lines" already fixed, new 
> SL version will be uploaded soon).
>
> Am 29.12.2013 02:43, schrieb Stefan Schäfer:
>>
>> Am 28.12.2013 23:33, schrieb Markus Vester:
>>> [...]
>>> PS Any progress on bypassing the divider in your VLF transmit chain?
>>
>> Aaah, no, i forgot that. So i cannot transmit OP32 on VLF because it 
>> would be incoherent then. So i have to key the PA via a VOX and OP32 
>> tones, still :-/
>>
>> In this H bridge PA config, an exact 50% duty cycle isn't needed, so 
>> i may actually remove the divider. But then i need a solid and 
>> defined input signal wave form! How do i get an inverted signal then? 
>> A transformer isn't possible since i like to have a wide frequency 
>> range of the PA. So far it works from 10 Hz to > 100 kHz. With the 
>> frequency divider, the wave form can be quite distorted, no problem 
>> unless the peak reaches the necessary voltage level. So maybe it is 
>> better to build the VOX circuit instead? Also i want to leave the PA 
>> circuit as it is, for nostalgic reasons :-)
>> Or do you have another idea? I remember that circuit with the XOR 
>> gates...
>>
>> 73, Stefan/DK7FC
>


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    <div class="moz-cite-prefix">Hello Markus,<br>
      <br>
      Ok .. i had assumed the problem was the flipflop (or binary
      frequency divider) which would be in an unpredictable state when
      not fed with a phase-coherent signal "in the gaps" (zeroes in the
      Opera- or whatever amplitude keyed signal).<br>
      This could be solved by providing the auxiliary output from the
      soundcard (at 2 * f_tx), to keep the divider chain running.<br>
      Depending on the MOSFET gate drivers, it may also be possible to
      feed the 'keying signal' to an output-enable-signal, but I'm not
      sure if that would put the driver output in high-impedance state
      (which would result in a catastrophic 'bang' if both FET gates
      were left floating). <br>
      <br>
      Anyway your suggestion with the xor gate may be the simpler
      variant than using two different output signals from the
      soundcard.<br>
      <br>
      73 and HNY,<br>
      &nbsp; Wolf .<br>
      <br>
      (p.s. just managed to build a transformer for a low-voltage MF PA,
      which transforms 0.6 Ohms drain load impedance to 12.5 Ohm with
      very low stray inductance.. using copper foil instead of wire, and
      thin adhesive tape ("Tesafilm") as insulator. But that's another
      story..)<br>
      <br>
      <br>
      Am 29.12.2013 12:00, schrieb Markus Vester:<br>
    </div>
    <blockquote cite="mid:8C09023FA2074CB380BC9CF1E7A514E3@White"
      type="cite">
      <meta content="text/html; charset=ISO-8859-1"
        http-equiv="Content-Type">
      <meta name="GENERATOR" content="MSHTML 8.00.6001.23543">
      <div><font face="Arial" size="2">Hi Wolf,</font></div>
      <div>&nbsp;</div>
      <div><font face="Arial" size="2">I think Stefan was only trying to
          solve the simpler problem of generating a dual squarewave
          drive for his VLF PA, and was not aiming for amplitude
          modulated output yet. So when he transmits Opera we'll just
          have to live with ultra-strong keyclicks, devastating the 9
          kHz band all over Europe ;-))&nbsp;</font></div>
      <div>&nbsp;</div>
      <div><font face="Arial" size="2">But I remember that in 2011 we
          discussed about transmitting high-quality&nbsp;Hell&nbsp;piccies. As you
          say, the Kahn technique with a separate AM modulator is
          certainly a good and efficient option. At VLF,&nbsp;outphasing (aka
          Chireix or LINC technique) between two half-bridges would be a
          valid alternative. There's some software for the purpose
          (including Basic source code ;-) on </font></div>
      <div><font face="Arial" size="2"><a moz-do-not-send="true"
            title="http://df6nm.bplaced.net/VLF/chirppix_outphase.zip
            STRG + Klicken, um Verkn&uuml;pfung zu folgen"
            href="http://df6nm.bplaced.net/VLF/chirppix_outphase.zip">df6nm.bplaced.net/VLF/chirppix_outphase.zip</a></font></div>
      <div><font face="Arial" size="2">This works in conjunction
          with&nbsp;your SndOutpt audio utility, generating the two
          outphasing carriers at the left and right stereo output.</font></div>
      <div>&nbsp;</div>
      <div><font face="Arial" size="2">Best 73,</font></div>
      <div><font face="Arial" size="2">Markus (DF6NM)</font></div>
      <div style="FONT: 10pt Tahoma">
        <div><br>
        </div>
        <div style="BACKGROUND: #f5f5f5">
          <div style="font-color: black"><b>From:</b> <a
              moz-do-not-send="true" title="mailto:dl4yhf@freenet.de
              STRG + Klicken, um Verkn&uuml;pfung zu folgen"
              href="mailto:dl4yhf@freenet.de">wolf_dl4yhf</a> </div>
          <div><b>Sent:</b> Sunday, December 29, 2013 9:12 AM</div>
          <div><b>To:</b> <a moz-do-not-send="true"
              title="mailto:rsgb_lf_group@blacksheep.org
              STRG + Klicken, um Verkn&uuml;pfung zu folgen"
              href="mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blacksheep.org</a>
          </div>
          <div><b>Subject:</b> Re: LF: VLF exciter</div>
        </div>
      </div>
      <div><br>
      </div>
      <div class="moz-cite-prefix">My suggestion:<br>
        <br>
        Use two outputs from the stereo soundcard: <br>
        An "amplitude" and a "phase" channel. The output from the phase
        channel will be a square wave, coherent, constant amplitude, fed
        to the divider chain. The "amplitude" channel delivers, well,
        the amplitude (as a waveform with variable voltage) which, after
        rectification, drives the final voltage via an additional
        mosfet. I think the software option is already there, and iirc
        it has been used (by Jim ?) for an LF PA.<br>
        This way, you could even use amplitude shaping if the bandwidth
        (from the hard-keyed PA) was a problem - which I don't think it
        is, on VLF.<br>
        <br>
        Cheers,<br>
        &nbsp; Wolf <br>
        <br>
        &nbsp;(p.s. problem with the "very long command lines" already fixed,
        new SL version will be uploaded soon).<br>
        <br>
        Am 29.12.2013 02:43, schrieb Stefan Sch&auml;fer:<br>
      </div>
      <blockquote cite="mid:52BF7E2A.9000002@iup.uni-heidelberg.de"
        type="cite"><br>
        Am 28.12.2013 23:33, schrieb Markus Vester:
        <blockquote cite="mid:DDBCC8F2ADC5452C85E1D13889D0C423@White"
          type="cite">
          <meta name="GENERATOR" content="MSHTML 8.00.6001.23543">
          <font size="2"><font face="Arial">[...]</font></font>
          <div>&nbsp;</div>
          <div><font face="Arial" size="2">PS Any progress on bypassing
              the divider in your VLF transmit chain?</font></div>
        </blockquote>
        <font size="2"><font face="Arial"><br>
            Aaah, no, i forgot that. So i cannot transmit OP32 on VLF
            because it would be incoherent then. So i have to key the PA
            via a VOX and OP32 tones, still :-/<br>
            <br>
            In this H bridge PA config, an exact 50% duty cycle isn't
            needed, so i may actually remove the divider. But then i
            need a solid and defined input signal wave form! How do i
            get an inverted signal then? A transformer isn't possible
            since i like to have a wide frequency range of the PA. So
            far it works from 10 Hz to &gt; 100 kHz. With the frequency
            divider, the wave form can be quite distorted, no problem
            unless the peak reaches the necessary voltage level. So
            maybe it is better to build the VOX circuit instead? Also i
            want to leave the PA circuit as it is, for nostalgic reasons
            :-)<br>
            Or do you have another idea? I remember that circuit with
            the XOR gates...<br>
            <br>
            73, Stefan/DK7FC<br>
          </font></font></blockquote>
      <br>
    </blockquote>
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