[hpsdr] Predistortion reference and comments

[Steven B. Dick]

A good overview of digital predistortion can be found in the following
Intersil datasheet in the theory section: 

http://www.intersil.com/content/dam/Intersil/documents/fn80/fn8039.pdf

I have worked with digital predistortion in a previous life.  It can work
extremely well. However, I'm a bit concerned about its operation with
different user's amplifiers.  A particular algorithm may work great for a
particular amplifier but poorly with another.  My philosophy is always to
keep it simple.  Although you may not get the best performance,  amplitude
correction only rather than amplitude and phase correction will work more
robustly over a wider number of different types of amplifiers and feedback
circuits, while still providing very good performance. Auto calibration
circuits are also problematic when trying to make them work with a variety
of tapoff circuits.   

Regards,
"Digital Steve", K1RF (electronics engineer/functional manager retired)