[RFI] An odd source of automotive RFI

[Pete Smith]

I've been sniffing for power-pole RFI using the radio in my truck, tuned to
a frequency high in the AM band.  Once I heard the buzz, I would go on foot
looking for specific sources at a higher frequency with a portable
short-wave radio.  Worked pretty well, except that my truck seemed to have
something in it that was often emitting a very loud, short chirp of RF
every .7 seconds or so.  I thought fuel pump, etc., but could never
correlate the noise's usual presence or occasional absence with anything
until now. 

Today, I accidentally found the answer.  I have one of Nokia's ubiquitous
analog cellular phones (a model 908?) plugged into my cigarette lighter
jack.  I had a tire inflater plugged in today, and when I started the
engine the radio was beautifully quiet -- plugged the cellular phone back
in, and chirp-chirp-chirp.  It appears that there's something in the
charging circuit of the phone that causes this noise, regardless of whether
the phone is on or off, so long as it is plugged in.  Disconnect the phone
from the car cord, or the car cord from the lighter jack, and it goes away.

Just FYI.

73, Pete N4ZR

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