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From: Johan Bodin <jhbodin@tele2.se>
Message-ID: <571F86BF.5050403@tele2.se>
Date: Tue, 26 Apr 2016 17:18:23 +0200
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Subject: Re: LF: TXing on VLF again, my first homemade linear PA! :-)
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Hi Stefan

I thought about your 9kHz PA efforts when I found this class D PWM chip 
capable of ~300W up to 100kHz with very low distorsion. Amazing 
performance from such a small $6 SMD chip!

http://www.ti.com/lit/ds/symlink/tpa3251.pdf

73 de
Johan SM6LKM

Den 2016-04-23 kl. 18:51, skrev DK7FC:
> Hi all,
>
> Since about 16 UTC i'm transmitting on 8270.00500 Hz again. The 
> antenna current is about 200 mA. It is a first test over a longer time 
> with my new PA.
>
> I have been off the air for a few days now becuase i destroyed my 
> audio amp that i used as a VLF PA. Somehow i started to like the idea 
> of a clean sine wave coming from the PA. Low pass filters are hard to 
> design for VLF, you know. Since i don't like buying and since i didn't 
> find another one in the trash, i 'had to' (actually /wanted/) to build 
> my own. It is a class-AB PA now running at 20V DC using 2x IRFP064N 
> against ground. Opposite phase drive signals are generated by a small 
> blue ferrite core with 20 quadfilar turns. On the primary side, 2 of 
> these 4 windings are in series. On the scope, the signal looks quite 
> good. The 3rd harmonic is at about -20 dBc, certainly improvable. But 
> it's just version 0.2 now ;-)
> A large ferrite core is used to up-transform the voltage to about 220V 
> rms for this power level (i'm not spot on the resonance), also 
> providing galvanic decoupling.
>
> A photo can be found at
> https://dl.dropboxusercontent.com/u/19882028/VLF/20160423_184046.jpg
> https://dl.dropboxusercontent.com/u/19882028/VLF/20160423_184059.jpg
>
> The PA consumes 3.6A at 20V DC now. Improvements will follow...
>
> The signal will stay on air for a few hours now.
>
> 73, Stefan


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    Hi Stefan<br>
    <br>
    I thought about your 9kHz PA efforts when I found this class D PWM
    chip capable of ~300W up to 100kHz with very low distorsion. 
    Amazing performance from such a small $6 SMD chip!<br>
    <br>
    <a class="moz-txt-link-freetext" href="http://www.ti.com/lit/ds/symlink/tpa3251.pdf">http://www.ti.com/lit/ds/symlink/tpa3251.pdf</a><br>
    <br>
    73 de<br>
    Johan SM6LKM<br>
    <br>
    <div class="moz-cite-prefix">Den 2016-04-23 kl. 18:51, skrev DK7FC:<br>
    </div>
    <blockquote cite="mid:571BA7FE.6080601@posteo.de" type="cite">
      <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
      Hi all, <br>
      <br>
      Since about 16 UTC i'm transmitting on 8270.00500 Hz again. The
      antenna
      current is about 200 mA. It is a first test over a longer time
      with my
      new PA.<br>
      <br>
      I have been off the air for a few days now becuase i destroyed my
      audio
      amp that i used as a VLF PA. Somehow i started to like the idea of
      a
      clean sine wave coming from the PA. Low pass filters are hard to
      design
      for VLF, you know. Since i don't like buying and since i didn't
      find
      another one in the trash, i 'had to' (actually <i>wanted</i>) to
      build
      my own. It is a class-AB PA now running at 20V DC using 2x
      IRFP064N
      against ground. Opposite phase drive signals are generated by a
      small
      blue ferrite core with 20 quadfilar turns. On the primary side, 2
      of
      these 4 windings are in series. On the scope, the signal looks
      quite
      good. The 3rd harmonic is at about -20 dBc, certainly improvable.
      But
      it's just version 0.2 now ;-) <br>
      A large ferrite core is used to up-transform the voltage to about
      220V
      rms for this power level (i'm not spot on the resonance), also
      providing galvanic decoupling.<br>
      <br>
      A photo can be found at <br>
      <a moz-do-not-send="true" class="moz-txt-link-freetext"
href="https://dl.dropboxusercontent.com/u/19882028/VLF/20160423_184046.jpg">https://dl.dropboxusercontent.com/u/19882028/VLF/20160423_184046.jpg</a><br>
      <a moz-do-not-send="true" class="moz-txt-link-freetext"
href="https://dl.dropboxusercontent.com/u/19882028/VLF/20160423_184059.jpg">https://dl.dropboxusercontent.com/u/19882028/VLF/20160423_184059.jpg</a><br>
      <br>
      The PA consumes 3.6A at 20V DC now. Improvements will follow...<br>
      <br>
      The signal will stay on air for a few hours now.<br>
      <br>
      73, Stefan<br>
    </blockquote>
    <br>
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