That's right Bob, complex indeed. Such linearization and intermodulation
distortion correction techniques are not the panacea they might first seem;
their practical implementation in ham-radio gear is not trivial and the
costs generally outweigh the meagre gains and benefit. As Paul points out
the other impediment for commercial equipment manufacturers is the complex
IP and licensing minefield.
For the average ham it's far easier to run an amplifier conservatively to
steer well clear of the amplifier's compression transfer curve where the
gain and Po depart from a linear relationship with input power, i.e.
practice power and drive back-off to attain maximum linearity.
The majority of common ham-radio amplifier tubes respond nicely to this
simple approach and yield sufficiently adequate IMD characteristics when
deployed in a well designed amp.
Compensation techniques to linearize an imperfect amp abound, but are not
simple to implement in a 1500 Watt PEP Tx system.
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Robert Carroll
Sent: Saturday, 4 May 2013 11:37 AM
To: amps@contesting.com
Subject: Re: [Amps] Pre-Distortion Linearizer
As a former Bell Labs design supervisor in the cellular wideband linear
amplifier design area, I can say that predistortion schemes as well as
feedforward linearization were being studied intensely and resulted in many
patents at BTL and elsewhere. It was a very complex problem both
practically and theoretically. The simpler means of incorporating
predistortion quickly became inadequate to meet FCC requirements as mobile
telephony moved away from its FM roots.
Bob W2WG
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Paul
Christensen
Sent: Friday, May 03, 2013 8:35 PM
To: amps@contesting.com
Subject: Re: [Amps] Pre-Distortion Linearizer
> Check out US Patent 4588958 by Allen Katz K2UYH. It's a common way to
> linearize solid state PAs for the cellular market back in the day.
Great info, Jeff. Looks like K2UYH has multiple, related linearization
patents. Also, thanks for passing on the references.
In looking at his patent citations, work really accelerated around the time
of the cellular industry explosion. I imagine AT&T/Bell Labs was faced
with similar spectral efficiency issues with its Long Lines carrier
microwave systems, but they had more usable licensed spectrum way up at 6 &
11 GHz where fixed, point-to-point communication is possible at those
wavelengths -- but not roving communications.
Often when the subject of pre-distortion comes up, the usual questions is
"why doesn't manufacturer X have this technology?" Peering through the
patent data is one reason why. It's easy for us to want the technology --
not so easy for the manufacturers to wade through the intellectual property
landmines or secure licensing agreements.
Paul, W9AC
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