Radio is very fuzzy and lacks an internal metal foil area

[treez]

Hi,

I have two DAB radios, a white one which has lots of bad fuzzy noise on it, and a black one which is fine.

However, the white one works fine when on batteries instead of the mains adapter.

I noticed that the (good) Black one has a metal foil area behind the main PCB (as shown in the attached).
The circuit ground is soldered to this metal foil.
The (Bad) White one does not have this metal foil. (as shown attached)

Both Black and White radios come with 5V,1A mains adapters, but the white one’s mains adapter is only 2/3rds the size of the black one’s. (I guess it also has less common mode filtering inside).

Anyhow, Do you think the metal foil in the Black radio acts like a kind of “chassis earth”, and helps in noise suppression?

__________---------------------__________________------------

Radio part numbers

***White one is Model No: ONNDAB001W
https://groceries.asda.com/product/...larm-clocks/onn-white-dab-radio/1000003249618

***Black one is Model No: DB482BLACK
https://picclick.co.uk/onn-DAB-Digital-FM-radio-DB482black-portable-163538005419.html#&gid=1&pid=1

 

[treez]

well.......................... i just switched the adapters (for white and balck radios) ....and it was just as bad.

I then switched the adapters back as before.......but removed the electrolytic capacitor from the little LC filter that i wadgered together (as shown attached), and now the white radio is working much better with its original mains adapter....Uuuuugh OK.

I have been walking around the room (because it usually goes fuzzy when my body is in a certain place in the room).....but now there seems to be far less places where i can go and cause it to go fuzzy.....now i am only able to make it go fuzzy when i go right up against the white radio.

The mysterys of RF.

So anyway…it seems that having that electrolytic capacitor in the LC filter that I put in there (as attached) was the problem…….so this seems to confirm that having too big diff mode capacitors in an input filter can actually make the common mode noise worse…this is because the common mode can jump through the big diff mode capacitors and get to the other rail, from where it can cause EM radiation and interference…….would you agree with this?
By the way, the only reason I removed the electrolytic was because when swapping the mains adapters, I accidentally reversed the supply….and presumed that maybe the electro cap was damaged…..it just shows that screwing up can sometimes be the best technique.

I always assume that noise problems in electronics are caused by common mode noise and not diff mode...since there is usually a decent diff mode filter so diff mode is never that bad....and also diff mode is at a lower frequency which cant jump about as much as high frequency common mode noise....common mode is highly infectious and can couple to things easily.

Seriously though, I always buy cheap radios, they usually get lost or smashed when I move flat. None have ever been perfect….all can go fuzzy at times. You find yourself moving the wretched things round the table to make the fuzziness stop. Consumer Radios are bound to be noisy. I wonder why anyone would ever buy an expensive radio?.....i mean, wont they still be fuzzy at times?....i mean, as is known, they have no earth connection……and so common mode filtering will be compromised.

 

[treez]

I removed the electrolytic capacitor from the filter in post #2 above, and now the white radio works fine.

The filter in #2 above, is one that i hacked in to the supply cable (from the mains adapter) to the white radio.
Why did removing the electrolytic capacitor in the filter of #5 make the white radio work nicely again?

When the electrolytic was in that filter, then the white radio worked just as badly as when the filter was not there at all.