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

[Flyback]

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

 

[rjenkinsgb]

The foil appears to be a kind of counterpoise or ground plane, a capacitive ground for the antenna cable braid.

You could try adding some self-adhesive copper foil to the one that does not have it? It's readily available on ebay as guitar screening foil.

 

[shortbus=]

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.

Maybe paint the white one black?

 

[Nigel Goodwin]

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?

No, I think there's a fault on the radio, or it's PSU - I'm presuming it's worked previously?, so the lack of the coating didn't make any difference before, why should it now?.

You see lot's of such things, yet while working on the radios you disconnect them - and they still work perfectly, with no changes. I've always presumed it was either to help in some fairly unlikely event, or just placed there as 'good practice'?.

 

[Flyback]

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

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)

 

[JimB]

Maybe paint the white one black?

Come on shortbus, you know you really mean this:

JimB

 

[Nigel Goodwin]

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)

I doubt that would make the slightest bit of difference - but feel free to give it a try.

For a more instant attempt, use a piece of aluminium foil - you can't solder to it, but you can tape a piece of bare wire to it.

 

[Flyback]

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.

 

[Nigel Goodwin]

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.

All of which has most likely no effect on operation whatsoever.

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. I've only ever bought two DAB radios, both cheap crap ones from Tescos, and their performance is 'OK' - but they were cheap enough to take the risk to see how well DAB worked.

It sounds like your issues are due to poor signal strength?, more than anything else - and a better performing radio 'may' cure that for you.

Essentially the cheap crappy DAB radios are designed for use in very strong signal areas, and DAB coverage still isn't that great anyway - no where near that of FM - the higher frequency also means poorer coverage.

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.

Back in my radio ham days I used to use a Trio/Kenwood 2200 145MHz portable, and these had the same issue. If you sat the radio on top of a car, this created the required ground plane, and performance was considerably enhanced.

So you might try placing your radio on top of your car, to see how it performs then? - must admit, I've never tried it with DAB, but the same RF principles apply.

 

[Flyback]

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?

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.

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

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.

.....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?

 

[Nigel Goodwin]

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?

Because the rest of it is far better, and probably much more sensitive and selective.