[hpsdr] predistortion

[Helmut, DC6NY]

Hi Frank,

Warren developed a fantastic highlight for the HPSDR stuff, which is more
worth than different other features.  Indeed LDMOS devices are easier to
tame with predistortion than BJT or TMOS due to less ‘memory’ behavior.
Typical for my new 250 W amp using the Freescale MRFE6VP6300HR:  28 dB gain@
50V Vdd, Iq=1,5A, IM3 < -60 dB on all band between 2 -50MHz. DL9SM, who is
developing a 500W single-stage LDMOS amp got similar results.
If people are interested I’ll try to put details of the amp on hamsdr.com.

73, Helmut, DC6NY

-----Ursprüngliche Nachricht-----
Von: hpsdr-bounces at lists.openhpsdr.org
[mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von Warren C. Pratt
Gesendet: Mittwoch, 8. Mai 2013 02:04
An: 'FRANCIS CARCIA'; 'HPSDR List'
Betreff: Re: [hpsdr] predistortion

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

Hi Frank,

I already have pre-distortion up and running in prototype form--using
full-duplex to collect the information to calculate the correction.  Samples
are continually collected during transmissions and correction is
re-calculated at intervals as desired.  There are still a few rough edges to
work out; however, testers with 50V LDMOS amplifiers are seeing typical
reductions of IMD from about -30dB (without pre-distortion) to about -60dB
(with pre-distortion).  12V FET and bipolar amplifiers are considerably more
difficult to correct as they typically have a much higher level of thermal
and supply-related memory effects.  There is a special configuration
required in firmware to facilitate collection of the samples; however, I've
implemented all the core algorithms in software--I can do the job much more
simply and precisely there than in firmware.

This is still prototype--not sure yet about a release plan.

73,
Warren  NR0V


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