[hpsdr] Hermes 2 design

[Kjell Karlsen]

Hi Dominic.

If the SMPSU on Hermes makes noise for you on 2 meter you can try to  
install a shielding box over it on the PCB. We planed to install this  
shield during the production but found that it was not needed as very few  
spurs can be seen and heard on HF. And without it, the cooling is a bit  
better.

What you hear must be radiated through the air so a shielded box should  
solve your problems.

If you do not have suitable tinned metal you can use some from old fashion  
tin!

And if you use a small loop connected to a Spectrum Analyzer, it is  
possible to see the noise spectrum coming from the SMPSU when the loop is  
held close to it. And you can also see spurs coming from the FPGA and LAN  
interface chip on VHF but none on the 2 meter band. If I test with the  
loop on the bottom side of the PCB, no noise is seen so I believe the  
shield should be very efficient.

In Hermes 2M we are going to use modern, low noise Switchers so we hope  
the noise will not be a problem. And we are also going to shield the input  
part of the RX,

73, LA2NI,Kjell.



På Thu, 10 Aug 2017 13:39:11 +0200, skrev Dominique Dehays  
<f6dro at wanadoo.fr>:

> ***** High Performance Software Defined Radio Discussion List *****
>
>
>
> Hello ,
>
> I am interested in the Hermes 2 design.
>
> I am actualy using an ANAN 10 , which is basicaly using an Hermes 1  
> board. There is  annoying issues occuring with the switching PSUs built  
> in on the board.
>
> 1) The psu is generating drifting birdies and these birdies are  
> seriously QRMing on 144Mhz.
>
> 2° the psu is dirty and generates spuriis on the tx signal.
>
> Maybe more filtering is needed .
>
> 73
> Dom/F6DRO
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