Re: LF: A transductor for power regulation?

[Markus Vester <markusvester@aol.com>]

Hi Stefan,

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

Without DC, the reactor will present high impedance, minimizing RF and supply current. You could use a small parallel C to tune out the large inductance.

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

Best 73,
Markus

-----Ursprüngliche Mitteilung-----
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,

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> 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