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Re: [Amps] pre-distortion

To: "Warren C. Pratt" <>
Subject: Re: [Amps] pre-distortion
From: Philip Townsend Lontz <>
Date: Sat, 18 Oct 2014 21:43:44 -0600
List-post: <">>
Warren, this wonderful! Thank you!
You have set my brain racing!

Don't learn to code... Learn to think!

> On Oct 18, 2014, at 9:29 PM, Warren C. Pratt <> wrote:
> Greetings,
> I sometimes monitor this list and I see that the topic of pre-distortion is 
> appearing recently in several posts.  I wrote the pre-distortion software 
> that was released a few months ago as part of the openHPSDR (open High 
> Performance Software Defined Radio) program.  I'll offer just a few 
> observations:
> ** It seems to me that it's probably much easier to optimally implement 
> pre-distortion in a DDC/DUC (digital up-conversion / digital down-conversion) 
> software defined radio than in other radios.  There are simply very few 
> places that errors can creep into the required processing.  The required 
> precision and accuracy increase exponentially as the desired reduction in IMD 
> increases. So, having few error sources and the benefit of double-precision 
> floating point become important.
> ** 50V LDMOS amplifiers are probably the "most correctable" solid state amps. 
>  Tube type amps also correct very well.  13.8V amps are more difficult due to 
> "memory effects."
> ** No problem to correct an entire amplifier chain, at legal limit. No extra 
> hardware or software is required.  One just feeds back a sample of the output 
> from the last stage to calculate the correction.
> ** You cannot successfully correct by pre-distorting the MIC input to a radio 
> UNLESS you have VERY wide bandwidth from the MIC through the entire 
> transmitter. The IMD frequencies that you want to correct must be within the 
> bandpass of the correction path.
> At Ham Radio Friedrichshafen this past June, I gave a talk (approx. 30 min.) 
> on the openHPSDR solution for pre-distortion.  It's posted on the openHPSDR 
> web site.  If any are interested, here's a link:
> "*Warren Pratt,*NR0V, 2014.Digital Predistortion linearizes RF amplifiers 
> <>(MP4)"
> This link is posted on the <> website on the Publications page.  
>  The video includes a few examples of amplifiers where this technology has 
> been applied.
> I hope this helps explain a little more about this technology and sparks more 
> interest in finding ways to reduce IMD!
> 73,
> Warren  NR0V
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