Today's Message Index:
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1. 01:44 PM - Re: Capacitor Installation for Ignition Noise (dwwilt)
2. 02:08 PM - Re: Re: Capacitor Installation for Ignition Noise (Paul Mulwitz)
Message 1
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| Subject: | Re: Capacitor Installation for Ignition Noise |
For a composite aircraft, I have fairly good grounds. I have an Arion Lightning.
However, grounding is always an issue for composites. Using a capacitor for
ignition noise in the radios has been a standard for many, many years. They
take the ripple out of the alternator output which can and does transmit RF.
In a composite aircraft, this is a real issue, more so than in an aluminum skinned
aircraft where the radios are basically shielded by the airframe.
Barry is spot on with his discussion and I need to determine what size capacitor
would be best. Cessna uses a 5.72 microfarad capacitor in it's system. And
yes, the leads need to be very short to reduce the capacitor's resonance frequency.
We don't want it transmitting in the audio or Nav/Comm range. I suppose
using both a large and small capacitor would be best as Barry suggests.
I assumed that since I have a Jabiru 3300 the ACU is a Jabiru unit and came with
the engine. I installed the engine, but the engine systems were installed by
the dealer.
Barry, are you speaking about installation on a Jabiru Engine or in general? BTW,
I am also an Electrical Engineer, but my design work was on integrated circuits
in the 80's.
--------
Dennis
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=370729#370729
Message 2
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| Subject: | Re: Capacitor Installation for Ignition Noise |
Dennis,
I've been about half following this discussion, and I too am a retired
EE. Let me make a few quick comments.
If you want to add a filter capacitor to the alternator I would be sure
to keep it small. If you put a large capacitor on an AC circuit it will
load it down rather than providing the RF filtering you seek. Large
caps can be put on DC circuits like your 12V supply, but you probably
don't need this. The power supplies in quality radios like your SL-30
will filter the input power quite nicely.
I think the key to getting rid of radio noise - especially when you have
high quality equipment - is to make sure you have a very firm ground
connecting all the electronics to the system ground point. You also
need to be sure you have properly shielded and grounded the audio cable
from your headset to the radio. This is usually isolated from the
system ground.
Good luck,
Paul
Camas, WA
On 4/13/2012 1:43 PM, dwwilt wrote:
> --> JabiruEngine-List message posted by: "dwwilt"<dwwilt@aol.com>
>
> For a composite aircraft, I have fairly good grounds. I have an Arion Lightning.
However, grounding is always an issue for composites. Using a capacitor
for ignition noise in the radios has been a standard for many, many years. They
take the ripple out of the alternator output which can and does transmit RF.
In a composite aircraft, this is a real issue, more so than in an aluminum
skinned aircraft where the radios are basically shielded by the airframe.
>
> Barry is spot on with his discussion and I need to determine what size capacitor
would be best. Cessna uses a 5.72 microfarad capacitor in it's system. And
yes, the leads need to be very short to reduce the capacitor's resonance frequency.
We don't want it transmitting in the audio or Nav/Comm range. I suppose
using both a large and small capacitor would be best as Barry suggests.
>
> I assumed that since I have a Jabiru 3300 the ACU is a Jabiru unit and came with
the engine. I installed the engine, but the engine systems were installed
by the dealer.
>
> Barry, are you speaking about installation on a Jabiru Engine or in general?
BTW, I am also an Electrical Engineer, but my design work was on integrated circuits
in the 80's.
>
> --------
> Dennis
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=370729#370729
>
>
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