[hpsdr] predistortion

Helmut, DC6NY dc6ny at gmx.de
Wed May 8 01:03:11 PDT 2013


Hi John,

of course you need LP filtering for LDMOS amps too. The necessary
unidirectional coupler for feedback to the RX input plug has to be
collocated behind the filter straight in the antenna line.

73, Helmut, DC6NY

-----Ursprüngliche Nachricht-----
Von: hpsdr-bounces at lists.openhpsdr.org
[mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von John Marvin
Gesendet: Mittwoch, 8. Mai 2013 09:41
An: hpsdr at lists.openhpsdr.org
Betreff: Re: [hpsdr] predistortion

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

Does this mean that you can run an LDMOS based amp without any form of low
pass filters after the final stage and still remain within FCC regulations?

John
AC0ZG

On 5/8/2013 1:15 AM, Helmut, DC6NY wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> 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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