I've posted this elsewhere, so if you've heard it before I apologize. I'm looking for a way to add a USB plug to charge my Iphone, without adding radio interference. The story so far: I've tried a large number of cheap usb adapters, some wired, some install in the lighter socket. All generate some amount of RF, some produce so much noise I can't use the radio. I've done many experiments with this, and I'm fairly certain that the cheap PWM chips pollute the power circuit, turning the entire wiring harness into an RF noise generator. The output seems to be well controlled, and the phone itself is no problem. I've tried various gadgets to filter this noise, including ferrite chokes, diodes, and capacitors. Nothing gets rid of it. So now I'm considering installing an aircraft certified ($$) USB adapter, on the assumption that the FAA wouldn't allow a noisy adapter for aircraft use. The other alternative is to wire up my own adapter using quality chips. I'm attaching a block diagram of what's inside one of these, for anyone interested. And here's the adapater I'm considering:

USB Charger Ports

What I'm wondering is if anyone has actually solved this problem.

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