[Amps] pre-distortion

[Roger (K8RI)]

Warren,  Thank you very much for this note.  By profession and degree 
I'm a software engineer
although having retired in 97, I'm afraid I've fallen far behind on both 
the hardware and software.  I retired at 57 so I could go play, but 
regret not having kept up.

My last class in the masters program was the design and analysis of 
algorithms.  IOW, putting the algorithms into mathematical formulas and 
running comparisons. Although I claim a Math minor, I do not claim to be 
good at it <:-))

Pre-distortion has interested me greatly, but I'm afraid I need to hit 
the books again although I'm not sure what reading would best serve me.

I would think pre-distortion  would involve a great deal of math in the 
algorithms to analyze the signals

With existing rigs, the band width required is not there that's required 
for the process, although with the SDRs, if the source code and 
algorithms are available, I would think they would lend themselves 
nicely to this process.

Years ago, my cousin (an Electrical Engineer specializing in machine 
code and now a SK) asked me about SDRs before anyone had openly heard 
about them.  He was interested in starting something up and wondered if 
I'd be interested.  I thought for a moment about old timers and their 
resistance to change and replied, "Nah, I doubt there'd be a place fo 
it"  Shows how good my predictions for the future are, <:-))

73

Roger (K8RI)


11:29 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 <http://video.openhpsdr.org/HRF2014/PureSignal1.2.mp4>(MP4)"
>
> This link is posted on the <openHPSDR.org> 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
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>