---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 01/09/12: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:18 AM - Re: Noise in damp weather (Robert L. Nuckolls, III) 2. 05:42 AM - Re: Noise in damp weather (Eric M. Jones) ________________________________ Message 1 _____________________________________ Time: 05:18:10 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Noise in damp weather At 03:06 PM 1/8/2012, you wrote: > > >Hi, > >I am hoping someone can give me some pointers in finding and >eliminating a problem. >I have a french built wooden aircraft with 0-200, B&C starter and >30Amp alternator. Narco radio and transponder with intercom. The >intercom is wired with shielded wiring as per the manufacturers instructions. > >This aircraft uses a negative earth, with a switch that is cable actuated. > >The B&C Alternator is wired as per the manufacturers diagram, using >a large capacitor on the DC Output. >All of the lighting and as many earths as I could find have been >wired independently to a "forest of earth" on the inside of the >firewall, connected by a brass bolt to another earth forest on the >engine side of the firewall. A heavy earth cable then runs from the >5/16" brass bolt to the engine. > >There is a skyflash strobe with strobe heads top and bottom of fuz. >On most frequencies there is a sharp crack through the radio as ea >ch strobe discharges. Never got to the bottom of this problem, >despite various attempts. This style of noise is usually RADIATED . . . I.e. comes directly from the strobe tube and is received through the receiver antenna. This is an easy thing to confirm but a TOUGH nut to crack. Check out chapter in the 'Connection on interference analysis. In this case, I'm pretty sure the noise you hear is affected by volume control on receiver which means the noise is coming in through the antenna. Proximity of the antenna to flash tube can be widened. Sometimes a fine wire, coarsely woven wire mesh shield over the flash tube grounded to base helps. This is one of the hardest noise issues to eliminate. >The few times, including today that I have been caught in rain or >very damp weather and have put the nav and/or landing light on I am >getting a loud buzz / shriek through the radio into the headsets. >This is normally silent in dry weather. >On finals today, the radio went dead, I thought a fuse had blown, so >I switched it off. When landed and clear the active I switched it >back on and it worked ok. > >I would appreciate any ideas on where to start looking for the >source of this noise in the wet weather. > >There is never any noise from the mags or the alternator. Man! Don't know where to even begin. Intermittent and/or special-conditions events can be very $hard$ to track down. One of my most satisfying victories involved tracking down a pushed back pin in a pressure bulkhead connector that would only manifest failure at very low outside ambient temperatures and in-flight. I had to develop an instrumentation system that we could read in the cabin to make measurements back in the un-pressurized 'hell-hole' while in flight. I found that I could tape ribbon-cable to the side of the fuselage and slip it through the door gaskets at each end to extend test signals to the cabin. Even then, we made several test flights to 41,000 feet in an airplane that cost a LOT of money to operate. I would have to hear the nature of your noise to even begin to identify its source. You might carry a hand held radio to see if the noise can be heard it in as well. Do the diagnostics steps defined in the chapter on noise. Is the squeal affected by volume control . . . position of switches power on intercom (does your intercom do a auto-bypass when powered down so you can still use the radio?). This can be a challenge but the problems you've observed DO have explanations in simple physics. Bob . . . ________________________________ Message 2 _____________________________________ Time: 05:42:22 AM PST US Subject: AeroElectric-List: Re: Noise in damp weather From: "Eric M. Jones" Chinesespaceman-- You DO have the ability to dry airplane and then wet one section at a time. Also, remember that WD-40 is really made for Water Displacement. It works extremely well at driving off water and displacing it with a non-conductive oil. There is not much downside to spraying electrical connections where leakage to ground or other connections might occur. -------- Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge, MA 01550 (508) 764-2072 emjones@charter.net Read this topic online here: http://forums.matronics.com/viewtopic.php?p=362815#362815 ------------------------------------------------------------------------------------- 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.