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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