On 7/11/2014 11:01 AM, Ignacy wrote:
Predistorsion properties are impressive. The following presentation
http://users.burlingtontelecom.net/[email protected]/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
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