---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Thu 09/13/07: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 07:09 AM - Re: 1 Amp Fuses (Chuck Jensen) 2. 01:16 PM - Re: Nav/com 'acoustic feedback' (Miskelly, Francis G) 3. 04:36 PM - Re: PTC (Robert L. Nuckolls, III) 4. 07:39 PM - Design Questions (MTBehnke) 5. 09:57 PM - D-Sub Pin Extraction () ________________________________ Message 1 _____________________________________ Time: 07:09:47 AM PST US Subject: RE: AeroElectric-List: 1 Amp Fuses From: "Chuck Jensen" The Chinese are building the old style fuse boxes with the screw in fuses. They were having trouble making the screw in fuses that fit in the fuse box. Every resourceful, they decided to supply each fuse socket with a penny on a string. This is considered an upgrade since the screw in fuse would only carry 5 amps but the penny...much more. Distributed by Mattel. :-) Chuck ________________________________ Message 2 _____________________________________ Time: 01:16:08 PM PST US Subject: RE: AeroElectric-List: Nav/com 'acoustic feedback' From: "Miskelly, Francis G" Feedback for the list This problem was due to the poor intercom on a Bendix/King 155 picking up radio interference and was solved by adding an external intercom (I've included the correspondence as it contains useful info) - Frank 1. The radio is a Bendix/King KX155 2. It is approximately 1 year old. Don't know the model # but could find out 3. It definately has an internal intercom but i've no links to describe it 4. I didn't check whether the sound varied depending on where your head/headset is sitting, or by bending the wires around on the headset, or the wires to the jack but it occurred with 3 separate headsets and on both pilot and co-pilot outputs. Pretty sure its not a headset problem as same headsets work fine in other planes 5. The noise gets worse with higher engine RPM but is very obvious even at 1000 RPM. The character doesn't change - just its loudness Many thanks Frank Interesting.. I wasn't aware that any KX155 has intercom. Okay. I see the manual says it has 500ohm aux inputs, but don't see any reference to intercom. We're talking about a Bendix/King KX-155, right? Do you have a link to a file which describes the feature? Does the sound vary depending on where your head/headset is sitting, or by bending the wires around on the headset, or the wires to the jack? Is the frequency of the whine/feedback dependent on the engine RPM? Or is it just a steady tone? I agree with item 3 (assuming an intercom). Regards, Matt- > Matt > 1. When i cover the mic with my hand (muff off) the character of the > feedback alters significantly but is not overall reduced. If i move the > boom away from my mouth and around to the back of my head then the > feedback reduces but doesn't disappear. Its worse (louder) the closer the > boom to my mouth. These symptoms occur on both left and right hand > headsets > 2. My KX155 has an internal intercom. I haven't tried to disconnect it. > 3. Plugging in the mic jack should activate the intercom and the transmit > on the radio (when PTT pressed) > 4. Remember the problem only occurs when the engine is running. > 5. Does anyone know how to adjust the mic gain (intercom volume control) > on the KX155? Couldn't find this info in the installation manual. > Kind regards > Frank > > > > > Does it help if you cover the mic with your hand (both sides - pull the > muff off)? > > I suspect that the input stage of your intercom is being overdriven by the > acoustic noise of the engine. > > > Regards, > > Matt- > >> Thanks for your comments Ernest. >> I've double-checked all the grounds i could find. Even took the whole >> harness out (which was new) and had it double-checked. Nothing found. >> If its the intercom in the radio why does it not cause the same problem >> when the engine is off? >> It only causes the problem when the engine is running >> Kind regards >> Frank >> >> ________________________________ >> >> From: owner-aeroelectric-list-server@matronics.com on behalf of Ernest >> Christley >> Sent: Mon 13/08/2007 15:04 >> To: aeroelectric-list@matronics.com >> Subject: Re: AeroElectric-List: Nav/com 'acoustic feedback' >> >> >> >> >> >> Miskelly, Francis G wrote: >>> The KX155 nav/com in my Glastar has 2 problems which may be related. >>> >>> 1. Inserting the headphone jack i have near perfect reception. >>> However, when i insert the microphone jack there is a loud whine >>> suggestive of 'acoustic feedback'. Moving the boom away from my mouth >>> reduces the whine. With a different headset it appears as lots of >>> static noise which again changes with position of the boom. I've >>> changed the aerial, power supply and checked all the earths. It occurs >>> with either mag and when the generator is disconnected. It only >>> happens when the engine is running. The radio's been bench tested and >>> passed as good. >>> >>> 2. Radio reception is good with just the headphone jack inserted. >>> However, insert the microphone jack and reception becomes very poor or >>> disappears completely. I suspect the 'acoustic feedback' is raising >>> the automatic squelch which is cutting off the radio station >>> >>> Can anyone suggest an explanation and a solution! >>> Many thanks >>> Frank >> Since there is a problem with multiple headset, I would check the jack >> first. The symptoms seem to imply some feedback from the mic to the >> audio. Look for a short or a broken ground. Beyond that, it would seem >> circuitry withing the intercom is fritzed, and it gets much more >> complicated. ________________________________ Message 3 _____________________________________ Time: 04:36:28 PM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Re: PTC At 09:24 AM 9/13/2007 -0400, you wrote: >all correspondence to the list should not use a acronym the first time a >item is used.. What is a PTC??? Positive Temperature Coefficient. The discussion was about the trade-offs for incorporating Polyswitches or their direct cousins . . . http://www.circuitprotection.com/polyswitch.asp . . .into the power distribution of light aircraft. Bob . . . ---------------------------------------- ( "Physics is like sex: sure, it may ) ( give some practical results, but ) ( that's not why we do it." ) ( ) ( Richard P. Feynman ) ---------------------------------------- ________________________________ Message 4 _____________________________________ Time: 07:39:01 PM PST US Subject: AeroElectric-List: Design Questions From: "MTBehnke" I have a few questions as I'm trying to work through my electrical design. I've looked through the Aeroelectric book and other sources, but can't seem to find answers to the following: 1. Is there some design guidelines for minimum fuse sizes to avoid nuisance trips? I've seen a couple of people mention keeping current below 80% of the fuse size. I also saw one recommendation on keeping below 50% for radios based on transmitting current draw. 2. I have the Creativair strobe power supply. I noticed that the strobe kit came with 22 ga. shielded wire to go from the power supply to the strobes. The installation instructions give Joules per flash, but nothing about voltage, current, etc. I don't have any way to validate whether 22 ga. is okay, especially as it's round trip distances. Should I just assume it's fine? 3. This may be overly nit-picky, but do you generally use 12 or 14 volts when calculating loads? For example, I have the Duckworks 100W landing light. Using 12V gives 8.3A versus 7.2A using 14V. On top of that, a 5% drop of 12V is 0.6V compared to 0.7V for 14V. I'm not sure if this would result in any different wire or fuse sizes. Thanks, -------- Mike Behnke RV-9A Fuselage Andover, MN Read this topic online here: http://forums.matronics.com/viewtopic.php?p=134314#134314 ________________________________ Message 5 _____________________________________ Time: 09:57:00 PM PST US From: Subject: AeroElectric-List: D-Sub Pin Extraction I need to reverse the direction of my autopilot roll servo. This involves swapping two wires that go into the servo D-Sub connector. I have extractred pins from D-Sub connectors before, but I always had a free end of the wire attached to the pin to thread through the groove in the extraction tool. This may be a stupid question, but how do I get the extraction tool around the wire when I don't have a free end to the wire? This would be easy if I had a free end to thread into the extraction tool groove, but a free end isn't available unless I cut the wire!? I sure don't want to cut the two wires, swap and then solder working in the belly of my fuselage! Am I missing something here? HELP! 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