[Elecraft] PA with predistortion

[Jim Brown]

On 7/11/2014 11:01 AM, Ignacy wrote:
> Predistorsion properties are impressive. The following presentation
>
> http://users.burlingtontelecom.net/~n1jez@burlingtontelecom.net/images/Eastern_VHF_UHF_Conf_2014.pdf
>
> gives some information what is possible. In LDMOS amp with bias almost
> reduced to 0, IMD3/5 change from -22/-28db to -55/-63db. Also a crappy 13.8V
> CB amp with IMD3/5 of -18/-28 becomes -47/-53 after predistortion.

I skimmed the presentation. There are no surprises. Several thoughts.

First, this is pretty complex -- that feedback (sense) loop from the 
amplifier output is critical. Why not simply buy a cleaner rig and amp, 
and run them under conditions that make it cleaner?  Study the 
presentation that K6XX and I did for NCCC last fall.  The measures that 
Bob talks about are very easy to implement.

http://audiosystemsgroup.com/K6XXAmpTalk.pdf

A decent tube amp, carefully tuned, is about as clean as the results of 
predistortion, and is a lot simpler.

Also, it seems to ignore phase noise, which is produced by the rig. It 
also ignores sidebands produced by distortion that results from 
overdriving audio stages.

FWIW, I see no reason for Elecraft to support it other than possibly for 
their own power amps. I suspect Wayne has looked at it.

73, Jim K9YC