Radio is very fuzzy, and has no internal metal foil area

Flyback said:

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.

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Flyback said:

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?

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No, I think there's a fault on the radio, or it's PSU - I'm presuming it's worked previously?,

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shortbus= said:

Maybe paint the white one black?

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Flyback said:

Thanks, but no, the white one never worked well on mains.
I have altered it now so probably wont be able to take it back (and dont have the receipt any more anyway).
But it has [a supermarket name] on its label, and surely the whole batch must be so afflicted, so they would maybe refund me i dont know.

I originally thought i could solve the problem by adding an LC filter just before the mains adapter isolated input to the radio...but this didnt work....i now think i should add this foil and solder it somehow to the ground braid of the coax piece? (coax shown in photo)

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Flyback said:

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.

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Basically the aerial on a DAB (or VHF) radio is a quarterwave whip - and these are really a 'dipole', with the other half of the dipole reflected in the ground plane that the whip is mounted on. 'What ground plane', you might say? - exactly - there's essentially no ground plane on a portable radio, so the aerial performance is compromised.

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People buy expensive radios because they are better designed, better made, using better quality components, and perform better. Basically you pay your money, and take your choice.

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Flyback said:

Thanks, ...just put the white radio on again .....and again its still working well.......this radio has been unuseable for the past 12 months since i bought it...but its now good!...wow....its playing music now without massive crackling!!!.....please tell how this is?.....

So the filter of #8 above is what fixed it...BUT with the electrolytic cap removed.........what was it about that electrolytic cap in that filter that made that filter not work?


Maybe the aluminium foil of the black radio of the first post is the ground plane you kindly speak of?


.....thanks, but as you say, no matter how much dosh we may pay, we simply cannot have a ground plane in the radio like is needed...so why bother paying anything above absolute cheapest for a consumer radio?

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