Ignition buzz on ra...
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Ignition buzz on radio after RX

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Hi Jabiru Forum. Got a Flysynthesis Storch HS year 2008 with Jabiru A2200 engine ser. no. 2637. Hours 330 whereof I have flown the 250 hours during the last 4 years. My radio is a 4 year old FUNKE ATR833 installed with a complete FUNKE harness. Two headsets. The antenna is located on top of the fuselage about 1 meter behind pilots head. My problem is that at the end of an RX (transmission received), I get a very loud very unpleasant buzz. When the radio is busy, eventually it almost kills the joy of flying. The buzz is the same continuos noise I get if I turn down the squelch to off. The squelch has got 10 levels, where level 1 is OFF and level 10 is maximum. Setting the squelch level to minimum ON level - which is 2, there is no buzz until I get an RX and then I get the buzz at the end of that RX. The buzz is there for average 1 second or so before the squelch manage to suppress it. Radio check with ground flight control or other aircrafts confirms good reception of my TX and also the RX quality is generally good.

It is quite clear to me that the noise is coming from the ignition. If I rev up the engine to i.e. 1800 rpm, and turn down the squelch to OFF the buzz is continuous. Then I briefly switch off the ignition switches. The buzz disappears instantly when both switched are OFF and the engine is still at high revolution. Also instantly comes back when ignition is on again. Same effect whether it is left or right switch being the last to switch OFF. Would you suspect my coils to be faulty and possibly causing the excessive noise, or which part of the ignition system would you expect to be the culprit of my problem?

If I want to replace my coils what would be the right choice today? I see there is an older version and a Honda version available. Are they interchangeable, or can I only use the same type as the original year 2008 versions I have got today? Coils and ignition cables are the same delivered in 2008. I have replaced the distributor caps and rotors 3 years ago, so they are approximate 200 hours old.

PS: I have made test with another FUNKE radio, and got similar, but not exactly, the same behavior from that too. Also I have made test with the radio being powered by a separate battery, so the radio system had no direct contact with the aircrafts electrical system. Same problem. This week made a test with a handheld ICOM A6 connected to the aircraft antenna. It seems the squelch of the ICOM is weaker, so it had to be turned up to high levels (levels are 1-24) before it suppresses the noise. Here I noted a difference between switching OFF left or right ignition. With only left ON the squelch must be at close to maximum (22 or more), while with only right ON the squelch can be turned down to level 15 before the noise breaks through.

Any advise will be very much appreciated.

Regards Olav