[hpsdr] 100W PA for Hermes

[Helmut Oeller]

Hi Kjell

I agree that the job gets more challenging the lower the supply voltage is. But too many cascaded stages with low gain will also reduce the IM3 performance. Assume for a 3 stage amp configuration   -predriver-driver- final- with -45dBc /-40dBc/-35 dBc IM3 ( no bad single values for class AB). In total you will achieve -29,5 dBc !
If you do the job with an 2 stage amp configuration, which seems possible for the required 25dB total gain, and assume further  -45dBc/-35dBc IM3. In total you will achieve now -32,5 dBc.

I did some preliminary test with IXYS FETs  XZ2210N50L@ 48V, 120W PEP and 16 dB gain: 
-38 dBc is achievable.
The only question is: Do people accept the 48 V supply. 

I think that the high IM3 performance of PENELOPE/HERMES requires adequate IM3 performance for the following amps.

73 , Helmut

-----Ursprüngliche Nachricht-----
Von: hpsdr-bounces at lists.openhpsdr.org [mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von Kjell Karlsen
Gesendet: Sonntag, 13. November 2011 21:00
An: hpsdr at lists.openhpsdr.org
Betreff: Re: [hpsdr] 100W PA for Hermes

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

Hi Helmut.

I have measured the IM3 on several commercial transceivers (Icom, Kenwood  
etc.) and the IM3 at maximum PEP is always specified at -30 dBc.  Only the  
most advanced and costly transceivers have better IM3 values at 100W PEP.  
Take a look at the tests done by ARRL.

At 12-14 Volt VDD it is very difficult to achieve better IM3. If you  
increase the voltage to 28, 48 or even >100 volt, the results are much  
better. I am looking at a solution using a high voltage MOSFET pair to get  
300W PEP. If this is a success, it will be a simple and low cost solution.  
The only drawback is the PSU but they are sold cheap on e-bay.

Normally a Power Amplifier is delivering the maximum legal power at a  
lower output than 100W from the transceiver and then the IM3 is better.

73, Kjell






På Sun, 13 Nov 2011 20:03:22 +0100, skrev Helmut Oeller <dc6ny at gmx.de>:

> Hi,
>
> is it right that IM3 is only -30 dBc? For my impression too bad when  
> driving a power amp.
>
> 73, Helmut
>
> -----Ursprüngliche Nachricht-----
> Von: hpsdr-bounces at lists.openhpsdr.org  
> [mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von Kjell Karlsen
> Gesendet: Sonntag, 13. November 2011 19:28
> An: hpsdr at lists.openhpsdr.org
> Betreff: Re: [hpsdr] 100W PA for Hermes
>
> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi Jeff.
>
> As Abhi say, I have constructed a 100W PA and I am finishing the final  
> PCB
> layout now.
>
> One lab model and 2 Beta boards have been built and tested and soon I  
> hope
> to get the results from two other builders in DL.
>
> After the modification of the output transformer the results are very
> good. Power output is > 100W PEP with >-30 dBc IM3 on all bands.
>
> I´ll post the measured results on
> http://openhpsdr.org/wiki/index.php?title=MUNIN soon.
>
> 73, Kjell
>
>
>
>
>
>
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>
>


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