Construction: how to shield CPU noise?


m_a_schuster
 

I'm not talking about noise from a nearby computer. I'm referring to hash generated by the radio itself, which then finds its way into the audio output.

 

Rare on Tecsun radios, I've seen it with cheaper brands but most especially with Degen models. Also Kchibo. Why some brands/models handle it well, and others not, is a mystery to me.

 

Sometimes it can't be fixed easily. The Ccrane pocket radio suffers from it. Their solution: add a button to turn of the display. Hmm. Well, it works.

 

Case in point: the Degen DE-11 (Kaito KA-11), an aging, tiny little PLL multiband styled like previous better-made Sony models. All of MW, and a good portion of SW, is drowned out by buzzing unless you have an S9 signal.

 

If one would attempt to add a shield, where would you start? At the source (CPU? display driver chip? how to identify) or the target? Any generic pointers from someone who has successfully tackked this kind of thing.


Guy Atkins
 

I added some shielding recently between the boards of the C. Crane Skywave radio, and have made similar additions to other portables before. My usual approach is to target the DSP chip first of all, and DC-DC converters or display driver chips if I can identify them.

Sometimes the extra screening works best if it is floating (not connected to a ground point), but usually grounding the shield is the way to go.

Construction-wise, I like to make up a sandwich of thin tin sheet metal with clear plastic tape on opposite sides for insulation. For the Skywave radio I didn't have any more tin sheet metal around so I used a layer of aluminum foil with the tape on both sides. Because I couldn't solder to the aluminum, I made a mechanical connection of a short length of wire under the tape, and then routed the wire to a ground point on the Skywave.

I'm not sure I noticed any noise level improvements with the Skywave, but I felt better knowing I'd added more extensive coverage than the minimal stock shielding. With other radios the improvement has sometimes been dramatic.

73,

Guy Atkins
Puyallup, WA


m_a_schuster
 

Thanks - sounds like a plan.


 


policow6@...
 

I think the Skywave already has the DSP noises well under control so I wouldn't expect much, if any improvement. But I got a huge improvement on the Eton Field 550 as I outlined in this article:


Eton/Grundig Field 550

and I would expect many other, especially earlier DSP radios with lots of spurious noises, could benefit greatly from some simple shielding.


Jay

http://radiojayallen.com