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Post by splischke on Jan 7, 2012 22:34:33 GMT -5
My GPASC Secondary Ignition causes RFI noise over my radio. The noise however, only happens when receiving a voice transmission. When no one is transmitting, there is no RFI noise. It seems RFI from the secondary ignition is piggy-backing (for lack of a better term) on the incoming broadcast. When I fly using only the magneto, there is no noise and I can hear other pilots much better. I'm using resistor spark plugs with unshielded automotive wires. Do you think ignition shielding braid like in this link www.aircraftspruce.com/catalog/elpages/shieldbraid.php is needed? Any other ideas how I can suppress this noise (other than turn off the ignition  ? -Scott |
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Post by n3480h on Jan 7, 2012 23:04:17 GMT -5
Does it also show up when using the Icom's internal battery (not connected to the main power bus)? If RFI is still a problem when running the Icom on its internal battery, then it is likely "broadcast" RFI the secondary is generating. In that case, shielding all ignition wires, including the small wires to-from the secondary, should help. Other options may include a bandpass filter or choke at the frequency - and harmonics - of the RFI. It can be hard to trace, but next time you have the cowl off and engine running, your radio's antenna may locate the source and all its branches for you. Set squelch and ANL to zero. It will get louder near the source. Just don't get too close to the prop! ;D
Tom
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ericm
New Member
Posts: 2
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Post by ericm on Jan 8, 2012 10:22:33 GMT -5
With the shielding braid and resistor plugs I was still getting RFI interference so I covered my coils with several layers of aluminum foil and that solved the problem. Be sure to keep the foil away from the primary hot lead. My coils are located on the passenger side of the firewall.
Eric
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hans
Full Member
Posts: 166
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Post by hans on Jan 8, 2012 11:39:43 GMT -5
if you go the shielded wire route, make sure you earth each of them on one side only. You don't want to create loops in your ground/shielding...
Hans
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Post by splischke on Jan 8, 2012 11:49:38 GMT -5
Eric,
I'll try shielding the coils first. A few pennies worth of foil or foil tape may be all I need. If that doesn't work, I'll shield the wires and switch to another brand resistor plug.
Did you have the same noise issue I have, that is, it's only heard when receiving a transmission from another aircraft and all other times the radio is quiet without a hum or crackling of any kind?
Thanks Eric and Tom for responding. You guys rock!
-Scott
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Post by paul57 on Jan 8, 2012 16:17:38 GMT -5
I have the coils on the engine side of firewall. I use resistor wires and plugs. Battery is located in tail and radio power wires don't run anywhere near the primary or high tension leads for either the mag or secondary ignition. The only time I have a problem is if the battery is low. Then I get a whine. Charge battery and it goes away. Been thinking about using resistor wires on the mag. Has anyone tried it ?
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Post by n3480h on Jan 8, 2012 17:46:54 GMT -5
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Post by oahupilot on Jan 9, 2012 2:27:42 GMT -5
make sure you are using suppressed or suppression spark plug cables
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Post by juergen on Jan 9, 2012 3:52:14 GMT -5
Hi Scott,
first, check, where the noise come in: through the antenna or through the power supply.
To check this, you can connect a external antenna with RG58 cable (about 15-30ft long), and pace the external antenna in line to plane behind the rudder. Then let the engine run and test it with friend radio.
If there is the noise with this test construction also, you must shield the coils ignition wires and don't forget the wire to the ignition switch.
In the other case, there is a problem with the power wiring. The optimal power wiring is, when all connection points for the loads are direct on the battery poles.
Where is your battery located?
Hope this will help.
with best regards
Juergen
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Post by gaston on Jan 9, 2012 8:49:31 GMT -5
Hi Scott
is this a new issue with you Sec Ign.
mine developed another type of issue in 2010 for an unknown reason,and I partly solved the problem by rerouting some wiring,and I found the culprit was the intercom.
I installed a condenser on it ,and the problem is almost completely gone...
I use R plugs on the Sec and non R plugs on the mag.
no shielded wiring ...
If you chose to cover your coils ,make sure the cooling air to the coils won't be disturbed...
BTW my sec ignition Keeps dry since oil seal was installed...
how about yours...
Gaston
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