I don't think anyone said it can't be done or hasn't been done before. It has. But you can't ignore the cost, reliability/ complexity, efficiency (power and signal) of the changes. For those of us that have actually had to design and implement circuit changes like this at the commercial level, it sounds trivial but that is simply not reality.
Dr. William J. Schmidt - K9HZ J68HZ email: [email protected] -----Original Message----- From: lmarion [mailto:[email protected]] Sent: Monday, September 14, 2020 11:32 AM To: Dr. William J. Schmidt <[email protected]>; [email protected] Subject: Re: [Elecraft] Why predistortion ? DC to DC is used in video and RF frequency, over 50 years I know of,all the time to get away from 60hz and other design nonlinearities. Retired NIST DC to 18GHz lab tech AB7CE Roy -----Original Message----- From: Dr. William J. Schmidt Sent: Monday, September 14, 2020 10:05 AM To: [email protected] Subject: Re: [Elecraft] Why predistortion ? Always tradeoffs to be made. Boosting 12V volts to 50V means some sort of converter that can add its own distortion products, plus expense and additional complexity (read that "reliability") and efficiency. There's no free lunch here. Dr. William J. Schmidt - K9HZ J68HZ email: [email protected] -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Charlie T Sent: Monday, September 14, 2020 6:30 AM To: [email protected] Subject: Re: [Elecraft] Why predistortion ? Maybe I'm missing something here, but it would seem to me that if an FET linear amplifier running from 50 V or higher is considerably cleaner than one running from 12 V, that, for a high end rig, a simple step-up switching supply could solve the problem. But, that obviously adds to the cost so it IS somewhat of a conundrum. However, implementing the pre-distortion function IS probably a better long-term solution. 73, Charlie k3ICH -----Original Message----- From: [email protected] <[email protected]> On Behalf Of David Gilbert Sent: Monday, September 14, 2020 12:43 AM To: Elecraft Reflector <[email protected]> Subject: Re: [Elecraft] Why predistortion ? Of course, but that's a conscious choice by Elecraft and it does not result in the "cleanest, purest signals around." I give Elecraft tons of credit for the other measures they have take to produce good signals, which is why I own and will keep my upgraded K3 probably forever, but K8JHR simply was incorrect in his comment and it makes a difference when considering the expanding focus by folks like Sherwood and others to clean up the bands. When it comes to IMD, Elecraft is not one of the better players. The fact that that's by choice doesn't change anything. I suspect that 95+% of K3 rigs are used in portable/emergency situations less than 5% of the time. 73, Dave AB7E On 9/13/2020 7:14 PM, Wayne Burdick wrote: > 12 volts is a severe constraint for MOSFET PAs. But, like a lot of > other manufacturers, we accept this constraint so the equipment can be used in a wide variety of portable/emergency power situations. As a result we have IMD numbers in exactly the same range as other products that are subject to this constraint. > > On the other hand, our transceivers are best in class in terms of transmitted keying bandwidth. See paper by K9YC for example. Perhaps that's what JR was thinking of. > > 73, > Wayne > N6KR > > > >> On Sep 13, 2020, at 6:50 PM, David Gilbert <[email protected]> wrote: >> >> >> I don't know where you got the idea that the K-Line produces the >> cleanest signals. As several people have pointed out, because of the 12 volt finals the transmit IMD performance of the existing K-line is relatively poor. >> >> Dave AB7E >> >> >> On 9/13/2020 2:32 PM, JR wrote: >>> Why are so many ops obsessed with predistortion? >>> >>> The Elecraft K-Line already produces some of the cleanest, purest transmit signals around. Do we need predistortion ? If so, why, and how much better is it than what we already have? Should I wait to buy a new rig until that is available? >>> >>> Thanks and Happy Trails to all. 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