Date: Wed, 19 Apr 2017 06:41:44 -0400
From: Markus Vester <markusvester@aol.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: A transductor for power regulation?
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Hi Stefan,

I think you'd have to do it the other way round, i.e. place the saturable r=
eactor in series with the load.=20

Without DC, the reactor will present high impedance, minimizing RF and supp=
ly current. You could use a small parallel C to tune out the large inductan=
ce.

Increasing the DC current will reduce the transductor impedance and increas=
e the output. Higher biasing will reduce the available B swing and voltage =
drop. At maximum output, you could then compensate the remaining stray indu=
ctance by a series C, or a slightly off resonant antenna.=20

Best 73,
Markus

-----Urspr=C3=BCngliche Mitteilung-----=20
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Mi, 19. Apr 2017 10:42
Betreff: Re: LF: A transductor for power regulation?


Hi Andy,=20

 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 cupbo=
ard. It didn't take much time to build up a 1:1 transformer. I took my smal=
l 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 r=
un a DC current into the saturating coil. The amplitude on the dummy load d=
ecreased 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 incr=
ease the resonance frequency of a HV mains transformer (antenna C =3D 480 p=
F 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 ce=
nter leg...

 73, Stefan


 Am 19.04.2017 08:59, schrieb Andy Talbot:=20

Stefan =20
your idea of saturating the transformer is, I think, flawed.    If you redu=
ce mu-r of the core by saturating with DC, the primary winding will have va=
stly reduced inductance and appear as a near short circuit to the transmitt=
er - 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 tr=
ansmitter 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> 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 tran=
sformer.
 Imagine you have a hard switching class D PA, H bridge or so. The output i=
s a constant voltage source and it is no problem to connect no load, as lon=
g as a proper type of low pass filter is used.
 Then imagine a simple 1:1 ferrite transformer, 50 Ohm to 50 Ohm. The trans=
former has a 3rd winding for a DC current (to compensate the AC component t=
ransformed from the RF windings, 2 cores must be used, which are in paralle=
l for the RF and anti-serial for DC).
 Then i can saturate the transformer with the DC so the =E7=9A=B4 falls dow=
n to 1.
 With this arrangement i could build a linear PA out of a switch mode PA, e=
ven a fast one, which avoids key-clicks, at least in QRSS-3 (you remember t=
he mode) or OP32 or even EbNaut on LF?
 Sounds like an interesting experiment at least. The question is how warm t=
he transformer would become when the RF output current is permanently reduc=
ed to 50%.
 Has someone ever tried that on LF/MF?

 73, Stefan
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<div style=3D"font-size:10pt;font-family:arial,helvetica,sans-serif;color:b=
lack;"><div style=3D"color: black; font-family: arial,helvetica,sans-serif;=
 font-size: 10pt;">Hi Stefan,<br><br>I think you'd have to do it the other =
way round, i.e.&nbsp;place the saturable reactor in series with the load. <=
br><br>Without DC, the reactor will present high impedance, minimizing RF a=
nd supply current. You&nbsp;could&nbsp;use a small parallel C to&nbsp;tune =
out&nbsp;the large inductance.<br><br>Increasing the DC current&nbsp;will r=
educe the transductor impedance and increase the output.&nbsp;Higher biasin=
g will reduce the available B swing and voltage drop.&nbsp;At maximum outpu=
t, you could then&nbsp;compensate the remaining stray inductance by a serie=
s C, or a slightly off resonant&nbsp;antenna.&nbsp;<br><br>Best 73,<br>Mark=
us<br><br>-----Urspr=C3=BCngliche Mitteilung----- <br>Von: DK7FC &lt;selber=
denken@posteo.de&gt;<br>An: rsgb_lf_group &lt;rsgb_lf_group@blacksheep.org&=
gt;<br>Verschickt: Mi, 19. Apr 2017 10:42<br>Betreff: Re: LF: A transductor=
 for power regulation?<br><br></div>
<div id=3D"AOLMsgPart_2_38a00ea7-1d23-45d9-8474-7e3e1eb30784">
<div class=3D"aolReplacedBody" text=3D"#000000" bgcolor=3D"#ffffff">
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 =3D
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=3D"about:blank">
  <div dir=3D"ltr">Stefan&nbsp;
  <div>your idea of saturating the transformer is, I think, flawed. &nbsp;
&nbsp;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. &nbsp; &nbsp;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 &nbsp;G4JNT</div>
  </div>
  <div class=3D"aolmail_gmail_extra"><br>
  <div class=3D"aolmail_gmail_quote">On 18 April 2017 at 17:18, DK7FC <span=
 dir=3D"ltr">&lt;<a href=3D"mailto:selberdenken@posteo.de" target=3D"_blank=
" rel=3D"noopener noreferrer">selberdenken@posteo.de</a>&gt;</span>
wrote:<br>
  <blockquote class=3D"aolmail_gmail_quote" style=3D"margin: 0pt 0pt 0pt 0.=
8ex; padding-left: 1ex; border-left-color: rgb(204, 204, 204); border-left-=
width: 1px; border-left-style: solid;">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 =E7=9A=B4 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>


</div>
</div></div>
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