[hpsdr] munin design

[Kjell Karlsen]

Hi Georg and Frank.

The latest version of Munin PCB has no connection to the center tap of L4,  
the PA transformer. The DC feed is through the bifilar windings of L3. I  
can confirm what George says about the IMD. Not installing any of the  
capacitors between L8 and L3 giver slightly better harmonic suppression  
and IMD but only a few dB.

For those who will test, it is possible to connect the center tap of L4 to  
L8. In fact I see absolutely no difference in power output or IMD. But the  
construction and material used in L4 is extremely important to get high  
output and efficiency and good linearity, especially on 50 MHz. This will  
be commented in my construction manual for Munin. At the moment more than  
250 boards will be ordered.

The latest schematics, BOM and Gerbers will be available soon.

73, LA2NI, Kjell






På Tue, 07 May 2013 11:04:13 +0200, skrev Georg Prinz <getpri at t-online.de>:

> ***** High Performance Software Defined Radio Discussion List *****
>
> Hello Frank,
>
> L3 acts as a dc feed choke so L4 does not saturate by dc current. L8 is
> for further decoupling and is important to get the L3 middle absolutely
> rf-cold. This has also an impact upon the IMD.
> L3 is wound bifilar, so at dc the current flows in opposite directions
> and the core does not saturate with dc eather.
>
> In drawing dated 04/03-2010 there are two links from L8. One to L4 and
> one to L3. I removed the link to L4. I guess this was a drawing done
> during the early design phase.
>
> 73, Georg, dl2kp
>
> Am Montag, den 06.05.2013, 16:27 -0700 schrieb FRANCIS CARCIA:
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> Hi All,
>> I have a question. Why does the Munin final feed DC into the
>> transformer CT. and also use a DC feed choke. I've never seen this
>> done before and wonder why. Frank WA1GFZ
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