[Elecraft] Why predistortion ?

[Joe Subich, W4TV]

On 2020-09-14 7:29 AM, Charlie T wrote:
 >
> However, implementing the pre-distortion function IS probably a
> better long-term solution.

Pre-distortion on a 12V rig only hides the problem.  Any "home
station" rig should have 28/50 V finals *and* then one can make
it even cleaner with pre-distortion.  If necessary, use 50V
capable finals at 50W maximum output for 12V operation and
150-200 W output when a 48V supply is available.

73,

    ... Joe, W4TV


On 2020-09-14 7:29 AM, Charlie T wrote:
> 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: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On Behalf Of David Gilbert
> Sent: Monday, September 14, 2020 12:43 AM
> To: Elecraft Reflector <elecraft at mailman.qth.net>
> 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 <ab7echo at gmail.com> 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.   K8JHR