The DC charger included in the Nokia "hands free" kit sold in a blister pack by
Cingular in its stores in this area (New York State now *requires* hands free
operation) is especially obnoxious in its emanations across the AM broadcast
band. The on-off rep rates of the offending interference (which sounds like a
squeal or "yowl" on the AM band) are even slower than those that Pete observed
from his adapter. This new Cingular adapter appears to have a printed circuit
card with surface mount devices on it; if I can figure out how to fully open
the case without breaking anything I'm going to see if I can clean it up.
I have powered earlier Erickson and Nokia handhelds with a variety of DC
adapters. At one time the DC charger sold by Cingular for the Erickson phones
was perfectly clean, but a third party charger I purchased for the same cell
phone put substantial broad band (but constant amplitude) hash in the car
radio, both AM and FM.
At 02:35 PM 2002-02-25 , Pete Smith wrote:
>my truck seemed to have
>something in it that was often emitting a very loud, short chirp of RF
>every .7 seconds or so.
>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. 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.