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sideslip(at)tiscali.co.uk
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 Posted: Mon Jan 15, 2007 1:27 am Post subject: Radio interference |
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I have a new Jabiru 2200 (85hp) installed in a Murphy Maverick with an Icom IC-A200 panel mount VHFand an external antenna mounted throughthe fuselage skin midway between the cabin and fin using the fuselage for a groundplane.
I am picking up ignition interference when receiving which increases with engine speed.
I have tried running the radio from an independant power supply to eliminate installation wiring and still get the same problem, which seems to indicate that the antenna is picking up the radiated noise.
Does anyone have any suggestions on how to cure the problem? Would a smaller insulated ground plane help?
Geoff Leedham
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jetboy
Joined: 22 Jul 2006
Posts: 233
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| Posted: Tue Jan 16, 2007 11:40 pm Post subject: Re: Radio interference |
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Geoff,
I just posted some info and plots of radiated noise from HT leads on
http://groups.yahoo.com/group/jabiruengines/message/16729
This might help although in your case it might also be alternator regulator noise.
I have shielded 'P' leads which made no apparent difference. The major cause for me is the HT leads and I have yet to try shielding or ferrite bead loading of the coil leads. Fitting the Bosch leads in place of the factory ones made the largest improvement. I use a Bendixking KY96A which is same as the A200.
Ralph
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Ralph - CH701 / 2200a |
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sideslip(at)tiscali.co.uk
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| Posted: Thu Jan 18, 2007 2:07 am Post subject: Radio interference |
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Hi Ralph
Thanks for the reply. When you replaced the leads did you replace the ones
from the coils to the distributer caps? The plug leads on my engine are
marked as suppressed but not the coil leads. Have you replaced the NGK plugs
with resistor types?
Geoff
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jetboy
Joined: 22 Jul 2006
Posts: 233
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| Posted: Thu Jan 18, 2007 9:05 pm Post subject: Re: Radio interference |
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Geoff,
You cannot easily change the coil leads, and they are wire.
I intend to shield one of them as an experiment and compare with the other. ferrite beads may also be a trial.
I use standard plugs. there is some debate about resistor ones and NIX plugs, but as my replacement ignition leads are already the correct resistance 3K - 8K adding a further 5K at the plug would add little suppression but might allow the coils to fail due to hihger voltages or the spark power to be weaker. Jabiru dont allow resistor plugs.
I suspect the distributors also are a noise source.
When we used to suppress radio inspectors vehicles we had to shield everything. That typically meant mounting a box around the distributor and sparkplugs and relocating the coil inside the box. It made a RF quiet vehicle but hard to service.
Ralph
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Ralph - CH701 / 2200a |
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jetboy
Joined: 22 Jul 2006
Posts: 233
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| Posted: Sat Feb 03, 2007 3:14 pm Post subject: Re: Radio interference |
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Updated the plots at
http://groups.yahoo.com/group/jabiruengines/files/Radio%20noise/
I also did bench testing; adding an R type plug and distributor spark gap to the setup to more closely represent the situation on a flying engine.
I could only observe the noise with the R plug on an older analyser (no plots available), however the noise reduction was a significant improvement over the normal plug and inductive lead combination (-5 dB).
The pulse observed at the coil output lead was not significantly higher when using a R plug; but it was higher with increased plug gap settings.
I now have no concerns about R plugs affecting coil reliability provided the specified gap is maintained. NGK DR9EIX is probably the best option.
If the inductive suppression lead is only available with low resistance (less than 1 K) then fitting R plugs would seem a good option.
Ralph
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