Improving Car Radio Reception While Charging Mobile Devices

M y FM car radio is hopeless when my iphone is charging. The charger is cheap and cheerful and I'm sure I could do better. A low efficiency non switch mode supply would do the job. Any ideas about a make?

I don't want to go down the road of chokes and tinfoil cos the car interior would look too geezerish for me,

"geezerish" LOL

Maybe borrow one from a friend to test it, then buy one like theirs if it works? Or buy from Apple, theirs will be good. Also, look for CE mark and/or FCC labels, those should have passed EMC tests.

I never thought of Apple!!
Thing is that wherever you look with a Google search, 'everyone' who posts has the problem but there are no serious solutions, apart from chokes and screening. If there's a simple inefficient regulated , that would do the job I'm sure.
Failing that, I could do with a new receiver with DAB option and that may cope with the problem. (sledgehammer to crack a nut perhaps)

sophiecentaur said:

If there's a simple inefficient regulated , that would do the job I'm sure.

For 5V out and 12V in, that's a 7V drop at about 1A charging, or 7 Watts of heat that such a charger would have to dissipate. Nice hand warmer in the wintertime...

berkeman said:

For 5V out and 12V in, that's a 7V drop at about 1A charging, or 7 Watts of heat that such a charger would have to dissipate. Nice hand warmer in the wintertime...

I have heated seats on one car but, in this second-best one I have no such luxury. I could huddle round the charger instead.

DaveE said:

Maybe borrow one from a friend to test it, then buy one like theirs if it works?

We have two cars, between us and a couple of spare chargers. I compared them all in the two cars and found that one charger, in particular, works best in both cars (our house is not well served by broadcast signals and is a good test bed) and one is definitely worst.

I have also found that the phone, when already charged (in the morning) makes little difference to reception on regular journeys. At night, going home, their reception tends to be worse when setting off (phone needs some charge after a day's use) but settles down after some time. It looks like the interference level depends inversely on the state of charge of the phone.

That could be due to the bigger dollops of charge that the SMPS puts into the battery, each cycle of switching. Reasonable??

In the end, I have ordered a grossly overpriced unit from the Apple Store so WE SHALL SEE!!!

sophiecentaur said:

In the end, I have ordered a grossly overpriced unit from the Apple Store so WE SHALL SEE!!!

Did you receive this yet? What were the results?

Well. Something else came up. The new one failed to connect reliably in the socket it was bought for. I couldn’t see anything wrong with the dimensions but it was fine in other sockets.
The other new one from the other car functions fine and produces no detectable interference and the posh one is fine in that other car.
That solves the problem. But there is an issue about sockets which are or aren’t powered when the ignition is switched off. The newest connector seems to have a fancy centre conductor with apparently two coaxial parts and a conical tip. What could that be all about? Could it be ‘smart’ in some way to avoid loading a permanently powered socket?
I don’t want to dismantle it (yet).

sophiecentaur said:

The newest connector seems to have a fancy centre conductor with apparently two coaxial parts and a conical tip. What could that be all about?

Sounds like it might be a "Kelvin" connection. A way to measure the source voltage without the load current effects. IDK, maybe a way of measuring input current as the voltage drop across something like a sense resistor? That sounds expensive though compared to a trace on a pcb.

Maybe EMI shielding? That also doesn't make a lot of sense to me. It's not like a long cable that makes a good antenna.

In any case, I'm guessing the center conductor carries the current and the outer one doesn't.

DaveE said:

Sounds like it might be a "Kelvin" connection.

Good thinking there,

I did c lean the centre connection at the bottom of the socket (and the sides) so I don't think there could be any open circuit. Weird.