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Date: Wed, 19 Apr 2017 10:41:45 +0200
From: DK7FC <selberdenken@posteo.de>
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Subject: Re: LF: A transductor for power regulation?
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Hi Andy,

Yes yes, i agree, and that's what i don't fully understand yet. Last 
night i played a bit with the transductor that is laying arround here in 
a cupboard. It didn't take much time to build up a 1:1 transformer. I 
took my small MF PA and a 50 Ohm dummy load. I watched the sine wave 
across the R with a scope. About 50W were passed through the 
transformer. Then i started to run a DC current into the saturating 
coil. The amplitude on the dummy load decreased but the PA consumed even 
more current! Not a good working point.
But then, how is this transformer working? It looks like it can only 
work in a series resonant circuit, as you say. So it is not really a 
transfromer.
Actually i built something similar a few months ago, when i wanted to 
increase the resonance frequency of a HV mains transformer (antenna C = 
480 pF switche in parallel to the HV winding). The idea was to saturate 
the two outher legs of the tripple leg transformer which has its 
windings on the center leg...

73, Stefan


Am 19.04.2017 08:59, schrieb Andy Talbot:
> Stefan
> your idea of saturating the transformer is, I think, flawed.    If you 
> reduce mu-r of the core by saturating with DC, the primary winding 
> will have vastly reduced inductance and appear as a near short circuit 
> to the transmitter - not what you want
>
> The idea of saturable reactors applies to resonant inductors, where 
> you use the DC to change the inductance.    So it could be applied to 
> a class D transmitter with a tank arrangement, to retune the tank 
> circuit to adjust for match, or control amplitude.
>
> Andy  G4JNT
>
> On 18 April 2017 at 17:18, DK7FC <selberdenken@posteo.de 
> <mailto:selberdenken@posteo.de>> wrote:
>
>     Hi all,
>
>     I'm just thinking about transductors and find them them quite
>     fascinating again. I read a bit Wikipedia and thought about the
>     use as a steerable transformer.
>     Imagine you have a hard switching class D PA, H bridge or so. The
>     output is a constant voltage source and it is no problem to
>     connect no load, as long as a proper type of low pass filter is used.
>     Then imagine a simple 1:1 ferrite transformer, 50 Ohm to 50 Ohm.
>     The transformer has a 3rd winding for a DC current (to compensate
>     the AC component transformed from the RF windings, 2 cores must be
>     used, which are in parallel for the RF and anti-serial for DC).
>     Then i can saturate the transformer with the DC so the 皴 falls
>     down to 1.
>     With this arrangement i could build a linear PA out of a switch
>     mode PA, even a fast one, which avoids key-clicks, at least in
>     QRSS-3 (you remember the mode) or OP32 or even EbNaut on LF?
>     Sounds like an interesting experiment at least. The question is
>     how warm the transformer would become when the RF output current
>     is permanently reduced to 50%.
>     Has someone ever tried that on LF/MF?
>
>     73, Stefan
>
>

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Hi Andy, <br>
<br>
Yes yes, i agree, and that's what i don't fully understand yet. Last
night i played a bit with the transductor that is laying arround here
in a cupboard. It didn't take much time to build up a 1:1 transformer.
I took my small MF PA and a 50 Ohm dummy load. I watched the sine wave
across the R with a scope. About 50W were passed through the
transformer. Then i started to run a DC current into the saturating
coil. The amplitude on the dummy load decreased but the PA consumed
even more current! Not a good working point.<br>
But then, how is this transformer working? It looks like it can only
work in a series resonant circuit, as you say. So it is not really a
transfromer.<br>
Actually i built something similar a few months ago, when i wanted to
increase the resonance frequency of a HV mains transformer (antenna C =
480 pF switche in parallel to the HV winding). The idea was to saturate
the two outher legs of the tripple leg transformer which has its
windings on the center leg...<br>
<br>
73, Stefan<br>
<br>
<br>
Am 19.04.2017 08:59, schrieb Andy Talbot:
<blockquote
 cite="mid:CAA8k23Tw_FZdRjH9qk6eEKGti_=mYnm6YXSp5KksH5q5BDcLWw@mail.gmail.com"
 type="cite">
  <div dir="ltr">Stefan 
  <div>your idea of saturating the transformer is, I think, flawed.  
 If you reduce mu-r of the core by saturating with DC, the primary
winding will have vastly reduced inductance and appear as a near short
circuit to the transmitter - not what you want</div>
  <div><br>
  </div>
  <div>The idea of saturable reactors applies to resonant inductors,
where you use the DC to change the inductance.    So it could be
applied to a class D transmitter with a tank arrangement, to retune the
tank circuit to adjust for match, or control amplitude.</div>
  <div><br>
  </div>
  <div>Andy  G4JNT</div>
  </div>
  <div class="gmail_extra"><br>
  <div class="gmail_quote">On 18 April 2017 at 17:18, DK7FC <span
 dir="ltr">&lt;<a moz-do-not-send="true"
 href="mailto:selberdenken@posteo.de" target="_blank">selberdenken@posteo.de</a>&gt;</span>
wrote:<br>
  <blockquote class="gmail_quote"
 style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Hi
all,<br>
    <br>
I'm just thinking about transductors and find them them quite
fascinating again. I read a bit Wikipedia and thought about the use as
a steerable transformer.<br>
Imagine you have a hard switching class D PA, H bridge or so. The
output is a constant voltage source and it is no problem to connect no
load, as long as a proper type of low pass filter is used.<br>
Then imagine a simple 1:1 ferrite transformer, 50 Ohm to 50 Ohm. The
transformer has a 3rd winding for a DC current (to compensate the AC
component transformed from the RF windings, 2 cores must be used, which
are in parallel for the RF and anti-serial for DC).<br>
Then i can saturate the transformer with the DC so the 皴 falls down to
1.<br>
With this arrangement i could build a linear PA out of a switch mode
PA, even a fast one, which avoids key-clicks, at least in QRSS-3 (you
remember the mode) or OP32 or even EbNaut on LF?<br>
Sounds like an interesting experiment at least. The question is how
warm the transformer would become when the RF output current is
permanently reduced to 50%.<br>
Has someone ever tried that on LF/MF?<br>
    <br>
73, Stefan<br>
    <br>
  </blockquote>
  </div>
  <br>
  </div>
</blockquote>
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