Marv,
> Look at Directed Energy, now owned by IXYS:
>
> http://www.ixyscolorado.com/
Oh yes, I'm watching them closely! Both for their linear and switchmode
RF FETs. I believe these are the best at the time.
Their fastest ones would already be good enough to work in class D on
the lower HF bands, easily to 40m, probably to 20m. Above that, I fear
bigger trouble. But anyway at this moment I'm too deep in other
projects. I hope in a year or so I might be able to pick this up again.
Maybe by that time they have that 1 nanosecond FET! That one will likely
require 100 amperes gate drive or so! :-)
> Here's the PDF I mentioned plus their patent application.
Thanks! I took a while to understand it, because I'm a bit weak in math! :-)
I wonder whether they did actually implement this, or if it is purely a
mathematical construction. Because I see flaws which they should have
noticed!
First: The feedtrough effect does NOT produce a DC offset of the
envelope, as they say. Since the feedtrough varies with applied drain
voltage, and is phase-inverted, teh real situation is quite a bit more
complex. Also, because the feedthrough is phase inverted, the additional
amplifier they use to compensate for the alleged DC shift should be
driven in the SAME phase, not inverted 180 nor 90 degrees, as they show!
It's probably me who is wrong, but I fail to see where my mistake is! To
me it really looks like this technique, and the patent for it, are flawed!
And even if it is correct, it wouldn't be applicable to an amplifier
used between an existing transmitter and the antenna. It would be only
applicable to a complete EER transmitter.
Clearly it seems that a class D amplifier, based on the fastest RF
switching FETs from Ixys, is a better bet!
Manfred.
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