Re: Automobile Cell Phone Charger RFI (MORE followup)

Rick Ellison

The charger is plugged into the 12v socket all the time and by itself I get no interference at all But as soon as I plug the USB cable into any device I have trouble hearing FM and it wipes out AM totally.. I looked at it today to see if it was easy to take apart but its not it is all glued togeather that would break it if I tried to separate it.


73 Rick N2AMG


From: [] On Behalf Of doug
Sent: Friday, August 31, 2018 1:41 PM
Subject: Re: [SDR-Radio] Automobile Cell Phone Charger RFI (MORE followup)



On 08/31/2018 01:32 PM, doug wrote:


On 08/31/2018 12:27 PM, doug wrote:

> I have a 4 port charger that makes listening to FM barely hearable and totally wipes out AM. I had never thought of using SDRC to track it down.

(see earlier post in thread.)



I just tested the 5 volt adapter I have. I connected it to a 12 volt power supply, and the output of the adapter to a CD Player with headphones. At the same time, I had an AM/FM portable radio
on the table about a foot away. Altho I have a fairly high AM noise level here, which I have not been able to find, the AM is perfectly clear, altho a bit noisy. I am about 60 miles from the New York City station.
There was no difference in the noise level with the power supply on or off. When on, I played a CD on the player, and it played clearly also. I then switched the radio to FM, and again, there was no
audible noise change when the CD was playing or when the power was off. Obviously, this is a linear voltage regulator design. (It should be noted that only one of the two negative input springs is connected.)
The power adapter has, as I mentioned, two USB jacks. It is marked "USAMS" on one side, and on the other side is marked in four lines, from top to bottom:
    "INPUT 12-24 VDC
    "OUTPUT 5V (polarity symbol) 3.1A
    "10 CE                                               <<<(the 10 is surrounded by two arrows in a circular pattern, one above, one below)

Hope this helps--Doug, WA2SAY

MORE followup:

Just in case the phone could be the problem--I didn't think it would be, but in the interest of science, I connected my cell phone thru its supplied charger cord to the adapter. The phone is a
Motorola "DROID" smartphone. It is charging perfectly and there is no difference in the AM noise whether the power supply is on or off.



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