Ah now Peter, those esoteric distortion correction linearization features
will unfortunately take a considerable time for us to see filter down to the
solid-state QRO amplifier systems used in the ham radio community :-(
The easier and more pragmatic approach is to over-design the SS amp's Po
capability, take the associated hit in efficiency on the chin, and operate
the amplifier well clear of its 1 dB power compression point...the resultant
linearity and IM performance will be "good enough" for all but the purists.
Keen experimenters can apply distortion correction technique for improving
the shape of the amp's intrinsic natural compression transfer curve and
thereby extract improved intermodulation distortion characteristics from the
FETS. A fairly simple analog linearity compensation approach using a pair of
log-amps for detectors, one on the input and one on output of the RF amp
feeding a comparator then the error signal drives a VCA; such a scheme can
make quite worthwhile improvements.
Also measures like using a diplexer style harmonic terminating LPF/HP
topology on the amp's output filtering can yield dividends in reduced IMD
and improved efficiency by eliminating the reflected strong H3 harmonic
energy messing up the FET drain waveform. These kinds of circuit design
measures can extract an impressive result from seemingly common or garden or
otherwise non remarkable extant RF power devices.
73
Leigh
VK5KLT
-----Original Message-----
From: peter chadwick [mailto:g8on@fsmail.net]
Sent: Wednesday, 11 September 2013 10:29 AM
To: Leigh Turner; amps@contesting.com
Subject: Re: [Amps] Future of RF AMPS
I am still waiting to see a review of a SS amp that is as good as the last
generation of tube amps when one looks at the generation of high order IM
products.
With pre-distortion and a totally digital tx, it can be done. With a linear
amplifier using Cartesian or Polar feedback, it can be done, but there
aren't any around of either type.
But with a straight linear amplifier, they will cause more splatter. Take
the REAL transfer characteristic of the device and calculate the higher IM
products....
73
Peter G3RZP
========================================
Message Received: Sep 11 2013, 01:51 AM
From: "Leigh Turner" <invertech@frontierisp.net.au>
To: amps@contesting.com
Cc:
Subject: Re: [Amps] Future of RF AMPS
Dick, there's no need to wait for such innovations in RF power
semiconductors as such a long awaited low cost S.S. 1.5 kW HF amp can be
economically homebrewed using a readily available multiplicity (6 devices in
parallel/push-pull) of cheap 50V RF MOSFETS sourced from the surplus market.
The overall BOM will not break the bank, and such a rewarding project is
well within the scope of the tech-savvy ham experimenter (that rarefied
breed that remains amongst us in 2013, as distinct from the ubiquitous
appliance operators).
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Richard
Solomon
Sent: Wednesday, 11 September 2013 9:59 AM
To: amps@contesting.com
Subject: Re: [Amps] Future of RF AMPS
I doubt I'll see this filter down to Ham Amps in my lifetime. I'm still
waiting for a decent SS Amp that runs 1.5 KW out and does not cost a
fortune.
73, Dick, W1KSZ
On Tue, Sep 10, 2013 at 10:03 AM, <donroden@hiwaay.net> wrote:
> Gold-Clamp Transistors
++SNIP++
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