Re: LTSpice simulation of uBitx Power Amp

K9HZ <bill@...>
 

Dunno about that.  I always design my LP filters at 50:50 ohms in and out... and my PA transformers are 50 ohms at the output.  I don't know why you would want to make the LP filter a transform too?


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

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On Feb 5, 2018, at 12:53 AM, John Backo <jabac@...> wrote:

Very good, Jerry.

However, note that the output is NOT 50 ohms until AFTER the LPF.
The input to the LPF is somewhat lower. And the WA2EBY has a voltage advantage
over the 12V input to the drains, though the output of the drains is closer to 50 ohms.

So it is a bit of a misnomer to assume that the drain load is 50 ohms. This is true, incidentally,
of any AB linear amplifier (and is probably one of the sources of oscillation). I should think that the
true drain load in this configuration is closer to 10 ohms than 50 ohms. The LPF transforms it
to 50 ohms for the antenna.

But it is not unreasonable to assume an overall load of 50 ohms. But be aware though, that one of the functions of
the LPF is to produce this. It is not quite true at the drains. The actual impedance at the drains is a function
of the first capacitor/inductance stage of the LPF. Things are not quite as simple as they seem...

john
AD5YE



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