[hpsdr] Predistortion reference and comments

[Helmut, DC6NY]

Hi Steven, 

Thanks for your input. Right, pre-distortion is new invention. Supplier of
3G and 4G cellular phone networks use this technique since years to
linearize their base stations. Even older systems will be reconditioned with
pre-distortion to make them capable for advanced LTE applications.
I’m just a minor tester since beginning of this year and I only tested 4
different solid-state amps up to 800 W output level. Best results could be
achieved with a new developed 300W LDMOS amplifier and more than 60 dBc (!)
IMD after linearization, i.e. approx. 30 dB improvement. Even a 2 stage
LDMOS/BJT array with 4 combined push-pull strips exhibits more than 50 dBc
IMD at real load (antenna). I didn’t test tube amps. I had the pleasure to
accompany the project as tester from the early beginning with manual
calibration using a ramp function to collect the different samples up to
current comfortable self-calibrating software version. It is tremendous what
Warren, Doug and Phil created in such short period of time. We owe a great
gratitude to these brilliant developers.

73, Helmut, DC6NY

-----Ursprüngliche Nachricht-----
Von: hpsdr-bounces at lists.openhpsdr.org
[mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von Steven B. Dick
Gesendet: Montag, 9. Dezember 2013 17:01
An: hpsdr at lists.openhpsdr.org
Betreff: [hpsdr] Predistortion reference and comments

***** High Performance Software Defined Radio Discussion List *****

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)


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