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correct shield grounding? - RF Cafe Forums

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 Post subject: correct shield grounding?
Posted: Thu Sep 29, 2005 5:14 am 
 
Lieutenant

Joined: Thu Sep 29, 2005 4:56 am
Posts: 3
Location: North West UK
Hello Gentlemen (& Ladies of course).
Newbie to the world of RF and need any pointers you can give.
I am building an amp and have introduced shielded wire for the input and power cables and wondered how or even if I should ground the shield to anything?
The case is aluminium and earthed to the mains. The input and grounding wires are, again, shielded up to their connection to the PCB and the potentiometer. I have made seperate compartments for the transformer and regulation circuits.
Should I leave the shielding or ground it to the case or, or, or?
Any help would be much appreciated.
Thanks

Lee


 
   
 
 Post subject:
Posted: Thu Sep 29, 2005 8:09 am 
 
Site Admin
User avatar

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 413
Location: Germany
Hello Lee,

You should apply your voltage supply to the amplifier through Feedthrough connector. This connector is a LPF that filters out any noises that are present in the supply rails. The connector is screwed to the case, and should be located close to the output of the amplifier in order not to add noise to the sensitive input.

The shielding of the wires should be connected to the aluminium case. You should form a perfect (As much as possible) ground plane from the input of the amplifier to its output. The GND of the supply voltage should be in the same potential to this ground plane, therefore you should connect it too to this ground plane. It is a good idea to make different compartments for the regulator, amplifier and transformer and by that to decrease potential coupling between these elements.

I hope this helps.

_________________
Best regards,

- IR


 
   
 
 Post subject:
Posted: Thu Sep 29, 2005 8:18 am 
Thanks IR, good feedback!
Should I look out for grounding 'loops' and only ground them at one end?


 
  
 
 Post subject:
Posted: Thu Sep 29, 2005 8:29 am 
 
Site Admin
User avatar

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 413
Location: Germany
You welcome!

Grounding loops usually appear in system with more than one ground e.g. in Mixed-Signal systems. If I understood your circuit, you use only an RF amplifier; therefore, you should connect all grounds point to the same ground plane and these points will be in the same potential, so essentially there is only one ground.

_________________
Best regards,

- IR






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