REFLECTOR: i pad / radio noise

[Brian Michalk]

You have the ElectroAire?

The coil packs have a very large dv/dt requirement.
I just pulled up the schematic, and it's not clear to me the current 
path for the coils, and they talk about "ground for the coil pack", but 
the schematic shows to connect the hot leads to a separate fused 
circuit, and then each coil has a wire to the controller.  Each wire is 
a leg on the return path.  What happens is battery+ -> coil -> 
controller-switch-to-ground -> ground.   This path needs to be handled 
properly.  By properly, it needs to be twisted wires, 14 to 16 gauge.

It looks like they lumped all of their grounds together (power and 
signal paths).  I hate it when they do that.  It really puts a lot of 
noise on the sensors.  You may not be able to separate out the coil 
grounds and the EI "computer" ground.  I wonder if J1 pin 2 labelled 
"remove" is in fact a ground pin that would allow access to the high 
current path?  Call ElectroAire, and ask them how one might be able to 
isolate this path?

The power to J2 is noisy.  The yellow J1 pin 6 power is low current to 
run the EI, and will not be noisy.  Make a twisted pair with ground and 
J2 power.  If this isn't possible, (and I cringe here) put a big 
capacitor across J2 and ground, as close to the coil packs as possible.  
This will level out the dv/dt spikes on the power wires.

On your power bus, where do you have the EI mounted?  You want your 
noisy stuff as close to the battery as possible, and if you can make a 
separate noisy power bus, even better.  Is it a big copper bar?  Feed 
your bus from the battery in the middle, noisy stuff on one side, quiet 
on the other.

I initially had problems with my Autronic using the supplied harness.  I 
made my own harness, and now everything is very quiet.  Not a single 
shielded wire in the mix.

Tell me about your alternator current path.

The power adapters are just cheaply made.  It could be emitting RF for 
all we know.

On 9/16/2013 4:22 PM, John Dibble wrote:
> On 9/16/2013 1:30 PM, Brian Michalk wrote:
>> There may be something wrong with your nav antenna.
> The nav works fine with the adapter unplugged, so I think the antenna 
> is good.  I have only one antenna.
>
>>   Do you have two nav antennas?  Try swapping them out, or make a 
>> temporary one and see if that works from inside the fuselage.
>>
>> The filter you are suggesting is to smooth out power surges/spikes, 
>> and is a different animal than RF, capacitive or inductive interference.
>> Try to borrow an oscilloscope.  They are very illuminating.  Put it 
>> on your mains bus, and turn loads on and off to see which is possibly 
>> making power surges.  You might be surprised at how some small relays 
>> throw spikes into your power lines.
> I have 2 low level noises.  One goes away when I turn off the 
> alternator and the other goes away when I turn off my EI, so I believe 
> I've identified the sources.  So what should I do next?
>
> John
>
>>
>> When you find a noisy load, troubleshoot that one only until it's 
>> nice and quiet.  Then repeat again.  It will usually reveal a bad 
>> crimp, ground loops or other things that will eventually bite you 
>> anyway.
>>
>> On 9/16/2013 12:58 PM, John Dibble wrote:
>>> Thanks, everyone for your comments. Here is where I'm at.  The 
>>> ferrite choke collar doesn't help. I tried another adapter and that 
>>> eliminated the radio noise, but the nav problem remains.  A mooney 
>>> stopped at our airport yesterday and he's using an adapter and 
>>> claims no problems.  I looked at it and tried to get the same one at 
>>> Walmart.  Flying in one direction, parallel to a VOR, it didn't seem 
>>> to help, but when I turned 180 degrees, the nav seemed to be working 
>>> correctly.  I'll get the exact model the next time this guy stops by.
>>>
>>> I want to put a filter on my alternator.  A Cessna filter was 
>>> recommended.  I understand it's a capacitor with a resistor. Can I 
>>> make one?
>>>
>>> Can I put one on my EI as well?  I get a little noise from both the 
>>> alternator and EI.
>>>
>>> John
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