[hpsdr] Predistortion and different types of amplifiers?

[Kjell Karlsen]

Hi.

I can confirm what Helmut says, the high voltage LDMOS transistors works  
extremely well with predistortion. It is much more difficult to get PAs  
using RD100HHF1 to work with PD. I have tested several Munin boards and  
the best improvement I can get is 15-20 dB. Increasing the Vdd to 24V does  
not help. And at higher frequencies the less improvements, sometimes I can  
get no reaction on 10 and 6 meter.

I see that some of the testers have achieved better results with ANAN-100  
so I do not understand why the two amplifiers behave different. The PA in  
Apollo using RD16HHF1 and the one in ANAN-10 using RD15HVF1 works  
perfectly with PD. I have also tested with lower bias current and even at  
100mA each, the improvements are good.

As the transistors are from the same family, it is difficult to explain  
this difference. Also the difference between Munin and ANAN-100 is  
strange. I have used other material in the output transformer that gives  
better efficiency but it is hard to believe this is the reason. So there  
is a lot of testing left to solve this problem. I am open for ideas!

73, Kjell



På Tue, 11 Feb 2014 12:14:41 +0100, skrev Helmut, DC6NY <dc6ny at gmx.de>:

> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi Rob,
>
> the currently used algorithm for adaptive pre-distortion can effectively
> improve IMD, independent of the type of amplifier (BJT, VMOS, LDMOS or  
> tube)
> or number of stages. The complete cascade will be linearized. Basically
> there is also no restriction on higher supply voltage or typical behavior
> without pre-distortion. Even class B amps can wonderfully linearized,  
> which
> reduces size and weight of necessary heat sinks.
> The efficiency in the current software version is limited by the so  
> called
> ‘memory effects’ of the intrinsic amplifier, caused by temperature
> migration, charging/discharging processes, specific ferrite  
> characteristics
> etc. We find out that the modern LDMOS series up to 1 KW is very
> ‘cooperative’ regarding to our demands.
> A lot of the wide TX noise Leif, SM5BSZ, is mentioning is also caused by
> noisy PLL- VCOs and pre-distortion can’t solve this problem. So we are  
> back
> by the significant benefit of our DDC/DUP architecture: No analogue  
> mixers
> or VCOs are employed. Reciprocal mixing is no issue.
>
> 73, Helmut, DC6NY
>
> -----Ursprüngliche Nachricht-----
> Von: hpsdr-bounces at lists.openhpsdr.org
> [mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von Rob Frohne
> Gesendet: Montag, 10. Februar 2014 22:08
> An: HPSDR list
> Betreff: [hpsdr] Predistortion and different types of amplifiers?
>
> ***** High Performance Software Defined Radio Discussion List *****
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