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1. 11:38 PM - Help with radio intereference (Andrew McMenamin)
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| Subject: | Help with radio intereference |
I hope someone can help me! I have little technical knowledge and may have
some of the technical terms incorrect but would appreciate any advice.
I fly a Skyranger with a Simonini engine, at a controlled airfield. The
Simonini is an Italian two cylinder, two stroke liquid cooled engine with
dual Ducati ignition; two plugs per cylinder. It performs best at over 5000
rpm. I have significant problems with noise on the radio. I have a
microair radio and a DRE 4000 headset. The radio is beautifully clear on
the ground with the engine not running. After start up, I get an RPM -
related interference which makes the radio very hard to hear over 5000 rpm -
i.e. at cruise. I am also told the Tower find it hard to hear me. I can
overcome it by reducing RPM to 4000 before transmitting but this is not
desirable!.
The interference reduces noticeably as I cut each magneto in turn at the
full power ground run up (when listening to the ATIS). This makes me think
it is ignition related.
The spark plugs are NGK resistor plugs. The plug caps are standard, no
resistor and non-shielded. The HT cables are NGK "racing" - i.e. copper
core, no apparent shielding.
The radio is positioned beside the two magneto switches on the dash, and
shielded by the aluminium firewall from the mags. It is not shielded from
the mag switch wires.
I suspect the problem is to do with the HT cables, or the plug caps, or
possibly the wires to the mag switches. I have read that I should not use
resistor caps when already using resistor plugs. Should I use different HT
leads??
Andrew
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