REFLECTOR: i pad / radio noise
Brian Michalk
michalk at awpi.com
Sun Sep 8 12:14:12 CDT 2013
One other note.
If you absolutely need to filter the stuff you have, and it's voltage
spike related, you band-aid it with a Pi filter.
http://en.wikipedia.org/wiki/Capacitor-input_filter
The caps try to maintain constant voltage, and the inductor tries to
maintain constant current.
This is a band-aid, and I would not recommend it. It's better to solve
the root problem, because it *will* come back and get you later.
To test this without an oscilloscope, set your multimeter to measure AC
voltage very close to the input to your adapter. I would have to
calculate a voltage threshold, but I'm guessing you should be seeing
less than 100mV AC on your DC power lines.
On 09/08/2013 12:04 PM, Brian Michalk wrote:
> I had a power adapter screw with my car. I bought another one, and
> the problem went away.
>
> When I build my circuit boards, the biggest noise problem I have is
> when a voltage regulator oscillates. It either needs more
> capacitance, or a lower resistance (ESR) capacitor to prevent the
> oscillation.
>
> I suggest getting a new power adapter. If that is not an option, take
> it apart and add some ceramic caps to any caps that already exist.
> Kind of difficult if you don't have an oscilloscope.
>
> No, shielding the cord most likely won't help. I'll bet it's noise
> injected into the power lines in the form of voltage spikes. It's not
> a radiation problem like magnetic or RF.
>
> On 09/08/2013 08:13 AM, John Dibble wrote:
>> I now understand why there is concern with the use of personal
>> electronics on commercial aircraft. Previously I reported erratic
>> radio noise. It was the same noise as I get when I pull the volume
>> knob to receive weak signals. Also my nav was not picking up VORs
>> very well. After a long discussion with an avionics technician I
>> decided to investigate my i pad. He said that because it's not
>> shielded, it can interfere. I had a hard time believing that because
>> many are using the i pad and no one else is complaining. However, I'm
>> using a power adapter and he said that can be a problem also. So I
>> tried unplugging the power adapter and, sure enough, the radio noise
>> went away. Also the nav came alive and picked up VORs like it
>> should. I also found that if I turned off the alternator, I could
>> leave the power adapter plugged in and the radio noise was gone.
>> This did not eliminate the nav problem, however. So now I'm turning
>> to the electronics wizards in the group to see if there is any way I
>> can have my power adapter and use it too. Would insulation around
>> the power cord help?
>>
>> Thanks,
>>
>> John
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