---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Sun 11/02/08: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:35 PM - COM-ELT INTERFERENCE (wschertz@comcast.net) 2. 01:26 PM - Re: COM-ELT INTERFERENCE (Bruce Gray) 3. 06:07 PM - Re: COM-ELT INTERFERENCE (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 12:35:27 PM PST US From: wschertz@comcast.net Subject: AeroElectric-List: COM-ELT INTERFERENCE I have just finished a composite airplane and am preparing for FAA inspection. Testing final systems, etc. I have run into a vexing problem that I need help with, when I transmit on COM 1, it triggers the ELT to start broadcasting. Transmitting on COM 2 does not cause the problem. Below are the facts that I have uncovered so far: Plane: KIS Cruiser, composite low wing 4 place airplane COM 1 SL-30 COM 2 SL-40 Intercom: PS Engineering 6000 COM2 Antenna Copper foil in vertical Stabilizer COM1 Antenna Bob Archer folded dipole on fuselage wall behind baggage compartment bulkhead ELT ACK Model E-01 ELT Antenna 18" whip with copper foil strips bonded to fuselage body to form ground plane, located close to centerline of compartment that COM 1 antenna is located. ELT has remote panel that allows you to reset the ELT if it is transmitting, along with flashing diode. Disconnecting this remote panel does not affect the behavior. Disconnecting the ELT antenna from the ELT, does not alleviate the problem If I insert my head and shoulders into the space, the problem goes away. As I withdraw, when I exit the compartment fully, the problem returns. Therefore it appears that having some mass/capacitance? near the antennas has a positive affect. What kind of better solution can be implemented/tried to eliminate this interference? I cannot carry a body around in that compartment because of weight and balance considerations. Bill Schertz KIS Cruiser #4045 N343BS ________________________________ Message 2 _____________________________________ Time: 01:26:52 PM PST US From: "Bruce Gray" Subject: RE: AeroElectric-List: COM-ELT INTERFERENCE You have to move the COM 1 antenna to give more separation or buy a higher quality ELT. The low end ELT's are susceptible to resonance from nearby transmitters broadcasting. The resonance causes the ELT to trigger. Most of the better ELT's have circuitry to block this action. Bruce www.Glasair.org -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of wschertz@comcast.net Sent: Sunday, November 02, 2008 3:28 PM Subject: AeroElectric-List: COM-ELT INTERFERENCE I have just finished a composite airplane and am preparing for FAA inspection. Testing final systems, etc. I have run into a vexing problem that I need help with, when I transmit on COM 1, it triggers the ELT to start broadcasting. Transmitting on COM 2 does not cause the problem. Below are the facts that I have uncovered so far: Plane: KIS Cruiser, composite low wing 4 place airplane COM 1 SL-30 COM 2 SL-40 Intercom: PS Engineering 6000 COM2 Antenna Copper foil in vertical Stabilizer COM1 Antenna Bob Archer folded dipole on fuselage wall behind baggage compartment bulkhead ELT ACK Model E-01 ELT Antenna 18" whip with copper foil strips bonded to fuselage body to form ground plane, located close to centerline of compartment that COM 1 antenna is located. ELT has remote panel that allows you to reset the ELT if it is transmitting, along with flashing diode. Disconnecting this remote panel does not affect the behavior. Disconnecting the ELT antenna from the ELT, does not alleviate the problem If I insert my head and shoulders into the space, the problem goes away. As I withdraw, when I exit the compartment fully, the problem returns. Therefore it appears that having some mass/capacitance? near the antennas has a positive affect. What kind of better solution can be implemented/tried to eliminate this interference? I cannot carry a body around in that compartment because of weight and balance considerations. Bill Schertz KIS Cruiser #4045 N343BS ________________________________ Message 3 _____________________________________ Time: 06:07:50 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: COM-ELT INTERFERENCE At 08:27 PM 11/2/2008 +0000, you wrote: > >I have just finished a composite airplane and am preparing for FAA >inspection. Testing final systems, etc. I have run into a vexing problem >that I need help with, when I transmit on COM 1, it triggers the ELT to >start broadcasting. Transmitting on COM 2 does not cause the problem. > >Below are the facts that I have uncovered so far: > >Plane: KIS Cruiser, composite low wing 4 place airplane >COM 1 SL-30 >COM 2 SL-40 >Intercom: PS Engineering 6000 > >COM2 Antenna Copper foil in vertical Stabilizer >COM1 Antenna Bob Archer folded dipole on fuselage wall behind baggage >compartment bulkhead >ELT ACK Model E-01 >ELT Antenna 18" whip with copper foil strips bonded to fuselage body to >form ground plane, located close to centerline of compartment that COM 1 >antenna is located. >ELT has remote panel that allows you to reset the ELT if it is >transmitting, along with flashing diode. Disconnecting this remote panel >does not affect the behavior. > >Disconnecting the ELT antenna from the ELT, does not alleviate the problem Your ELT was probably not qualified to conditions that are now routinely levied on new designs for resistance to high-intensity radio frequency fields. These antagonist fields have always been around and include transmitters of all types aboard the aircraft including comm, xpndr, dme, radar, hf, telephone services, etc. External antagonists include radio and television stations, ground and airborne radar, etc. We had little need to concern ourselves with these threats before plastic airplanes came along. It's almost a sure bet that your ELT is suffering a HIRF moment due to proximity of the transmitting antenna. A useful experiment is to swap atennas between the two comm radios and see if the antagonist shifts to the other radio. >If I insert my head and shoulders into the space, the problem goes >away. As I withdraw, when I exit the compartment fully, the problem >returns. Therefore it appears that having some mass/capacitance? near the >antennas has a positive affect. > >What kind of better solution can be implemented/tried to eliminate this >interference? I cannot carry a body around in that compartment because of >weight and balance considerations. Assuming the experiment described above confirms vulnerability to signals emitted from the close proximity antenna, Just because the Com 2 radio doesn't trip the ELT doesn't mean that it's sufficiently weak to NEVER trip it. The fact that your body alters the coupling between antenna and ELT sufficiently to stop the problem suggests a marginal condition . . . that could shift either way with either radio in time. This is why we test most devices at 10x to 100x the energy we ever expect them to see. LOTS of head-room! I'd go for shielding the ELT. Is this one of those plastic case things? Alternatively, you would need a better location for the ELT or the offending antenna. But shielding is likely to offer a 10x reduction in coupling for both radios and be a much more robust solution. Have you talked to the ELT folks? This can't be the first time this has happened. But if push comes to shove, you can get a really whippy GPS enhanced crash-locator beacon that's about 100x more likely to get you found than a 121.5/243 ELT. See: http://www.marvgolden.com/elt-encoders/acrterrafix.htm An aluminum foil shield that is connected to the outer shell of the antenna coax connector may make your problem go away. Bob . . . ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.