---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 06/08/09: 7 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:34 AM - RF interference fix? (Robert L. Nuckolls, III) 2. 04:41 AM - Re: RF interference fix? (Robert L. Nuckolls, III) 3. 05:32 AM - Stero to Mono (Robert L. Nuckolls, III) 4. 06:37 AM - Re: Stero to Mono (j. davis) 5. 07:25 AM - Re: Stero to Mono (Robert L. Nuckolls, III) 6. 07:26 AM - Re: xponder ant mounting (Robert L. Nuckolls, III) 7. 08:42 AM - RF interference fix (Erich_Weaver@URSCorp.com) ________________________________ Message 1 _____________________________________ Time: 04:34:11 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: RF interference fix? At 11:27 AM 6/7/2009, you wrote: From first flight, the GRT EFIS and EIS on my RV have indicated momentary, anomalously high fuel pressure readings, typically just before take-off and also when entering and in the pattern. Stewed over that for over a year before asking myself the question - how does the system KNOW Im going to takeoff or land? Asking that question led me to the only possible answer: it knows because I get on comm and announce it! A couple of weeks ago I confirmed this - every comm transmission resulted in a sharp rise in fuel pressure. Yesterday I took it a step further, seeking to determine what the propogation mode was, and reasoned it was either RF interference or some sort of magnetic coupling associated with the increased power requirements during comm transmissions. The easy test was to get out my battery operated handheld transceiver and transmit from inside the cockpit with the engine running and the EFIS/EIS powered up, so I did that first. Bingo - a similar increase in the fuel pressure reading, although to a lesser degree than with ship's comm. This is not an uncommon problem with products offered to the OBAM aircraft community. In the TC aircraft world, we have to demonstrate immunity from commonly encountered radio frquency stresses in the lab during qualification tests. Some of the instruments offere by Van's have demonstrated sensitivity to VHF comm signals from ship's transmitters. Talk to GRT first. They have certainly encountered this before. They know their product better than anyone else and should be able to recommend some filtering . . . probably compoents added at the connector where the pressure transducer wires come into the indicator. Don't be surprised that there isn't a fix either. These issues are realtively easy to fix during prouduct development and qualification . . . but MUCH more difficult later. Also noticed a lot of noise on my handheld when receiving from inside the cockpit - noise that isnt noticeable on ship's comm, nor on the handheld normally.So, now Im feeling pretty high and mighty with my diagnostic skills, but the problem still remains - where do I go from here to fix this? Igntion noise? The best way to enhance the performance of a hand held transceiver is to provide connections to the ship's regulator comm antenna. I used to recommend a coiled loop of coax within reach of pilot in the cockpit that could be opened with a pair of in-line connectors. http://www.aeroelectric.com/Pictures/Connectors/Coax/BNC_Cable_Female_1.jpg http://www.aeroelectric.com/Pictures/Connectors/Coax/BNC_Cable_Male.jpg Put the cable-male on the feeder that goes to the the antenna and leave enough slack in it to allow connection to the hand-held. A pair of right-angle coax adapers http://www.aeroelectric.com/Pictures/Connectors/Coax/BNC_Rt-Angle_Adapt_2.jpg can be used to do a small radius 180 degree turn in the coax so that it will lay against the back of the hand-held and exit downward. Bob . . . Bob . . . --------------------------------------- ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) --------------------------------------- ________________________________ Message 2 _____________________________________ Time: 04:41:00 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: RF interference fix? At 06:31 AM 6/8/2009, you wrote: > > >At 11:27 AM 6/7/2009, you wrote: > The easy test was to get out my battery operated handheld > transceiver and transmit from inside the cockpit with the engine > running and the EFIS/EIS powered up, so I did that first. Bingo - > a similar increase in the fuel pressure reading, although to a > lesser degree than with ship's comm. P.S. You may find it more practical to live with it. After one understands how the problem manifests itself then it may be easier to just let it go. I've had several customers who've elected to not pursue a best-we-know- how-to-do fix when the $time$ associated with the fix was going to be pretty high. Bob . . . --------------------------------------- ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) --------------------------------------- ________________________________ Message 3 _____________________________________ Time: 05:32:46 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Stero to Mono At 06:40 AM 6/4/2009, you wrote: Greetings... I'm a bit confused on this subject after reading this thread and similar threads in other lists. I have the same objective: plug my iPod into my Xcom 760's audio in. The Xcom's documentation says to use a 3.5mm mono jack in combination with a stereo-to-mono adapter plug. My thought was to eliminate the adapter plug by simply jumping the left/right channel pins on the jack itself, and this does indeed give [seemingly] good results with both channels clearly heard. But lately I've read that this may damage the iPod, and I should be using resistors/capacitors and/or the adaptor, as though the adaptor had some components built into it's small, moulded little case. I'm relatively sure that this adaptor plug is doing nothing but physically joining the left and right channels from the stereo plug into a single tip on the mono plug, and is in no way electronically 'magic'. Not wanting to damage my iPod, I'd be interested to know the science behind all the posts saying 'don't do it' (wire the left and right together), use the adaptor plug. Thanks! The roots of this thread go back a few years. The first adaptation I recall of a common commercial stereo music product into an OBAM aircraft was for a builder wanting to adapt a compact automotive AM/FM radio to his airplane. In fact, he had pulled a non-working ADF and was plugging the hold with the automotive receiver. He missed the ADF's ability to turn the AM radio stations. This was before car radios featured low-level audio output/input jacks. The only outputs were intended to deliver WATTS of energy to speakers. Voltage levels at the speaker output of such radios were much higher than necessary to service the headphone level inputs to intercom systems in tens of milliwatts. The task then had several considerations. The output stages of the radio were designed to deliver energy to low resistance loads (4 ohm speakers). If not similarly loaded in this new application, audio quality at low output levels might suffer (cross-over distortion). So the first thing we did was "load" the radio with some handy but relatively low value resistor . . . 10 ohms, 1 watt was common. After that, the too-high output voltage needed to be attenuated to levels appropriate to headphone input levels at the intercom. At the same time, the right-left stereo signals needed to be mixed in a manner that provided a summation of the two signals, not a conflict. By conflict, I mean that simultaneous positive and negative going transients in program material do not cause large currents to circulate between the right and left amplifier output stages. The risk for damage to the system is low. The strongest effect for these circulating currents is distortion of the audio. It's common practice to first reduce the potential for circulating currents between the two outputs by artificially raising their output impedances (series resistors) and then setting the system losses with a downstream load (parallel resistor) to set volume. In this example http://aeroelectric.com/Pictures/Schematics/WalkmanAdapter.gif only mixing resistors are called for but if the signals from the audio source proved too strong, a resistor on the order of 10 to 100 ohms could be paralleled with the output to bring the level down to size. Bob . . . --------------------------------------- ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) --------------------------------------- ________________________________ Message 4 _____________________________________ Time: 06:37:01 AM PST US From: "j. davis" Subject: Re: AeroElectric-List: Stero to Mono Robert L. Nuckolls, III wrote: > > The roots of this thread go back a few years. The > first adaptation I recall of a common commercial > stereo music product into an OBAM aircraft was for > a builder wanting to adapt a compact automotive > AM/FM radio to his airplane. In fact, he had pulled > a non-working ADF and was plugging the hold with the > automotive receiver. He missed the ADF's ability to > turn the AM radio stations. > ---------------snip ------------- Thanks so much for this inclusive explanation, Bob. In my particular case, though, I *think* it's safe to assume that the modern Xcom 760 radio is designed with iPod/CD player input in mind, and that any attenuation/gain/amplification is done on the radio's c.b. The fact that the manufacturer states to simply use a 3.5mm mono jack along with a stereo-to-mono adapter plug from the iPod headphone out, enforces this assumption, in my mind. My question, really, is if shorting the ring and tip pins on a stereo jack installed on my panel is the electrical equivalent of using the adapter plug. Which begs the question: do those adapter plugs contain any sort of electronic components at all? Since the price of these critters ranges from $1.00 at the Dollar store to $9.95 at the Source (Canadian Radio Shack, gold plated), perhaps the high-end ones do, but I doubt it. The sound is good the way I've got it (jack pins connected), hearing both channels mixed, good volume. Just don't want to put my little iTouch at risk, as some have implied I may be doing... Thanks, again! -- Regards, J. Sonex C-FJNJ, Jab 3300, Prince P-Tip http://cleco.ca +-------------------------------------------------------------+ | J. Davis, M.Sc. | (computer science) | | *NIX consulting, SysAdmin | email: jd at lawsonimaging.ca | +-------------------------------------------------------------+ and now... Deep Thought #35, by Jack Handy When you go in for a job interview, I think a good thing to ask is if they ever press charges. ________________________________ Message 5 _____________________________________ Time: 07:25:40 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Stero to Mono >Thanks so much for this inclusive explanation, Bob. In my particular >case, though, I *think* it's safe to assume that the modern Xcom 760 >radio is designed with iPod/CD player input in mind, and that any >attenuation/gain/amplification is done on the radio's c.b. The fact >that the manufacturer states to simply use a 3.5mm mono jack along >with a stereo-to-mono adapter plug from the iPod headphone out, >enforces this assumption, in my mind. Yes, we're talking headphone levels for signal strength in both the aviation and the pocket entertainment world. These voltage levels are on in the ballpark with votlages that are exchanged between component systems on their line-in/out jacks. >My question, really, is if shorting the ring and tip pins on a >stereo jack installed on my panel is the electrical equivalent of >using the adapter plug. Which begs the question: do those adapter >plugs contain any sort of electronic components at all? Since the >price of these critters ranges from $1.00 at the Dollar store to >$9.95 at the Source (Canadian Radio Shack, gold plated), perhaps the >high-end ones do, but I doubt it. The sound is good the way I've got >it (jack pins connected), hearing both channels mixed, good volume. >Just don't want to put my little iTouch at risk, as some have >implied I may be doing... The only way to see if there are components included inside the adapter is to research it from outside with test equipment. I suspect they have none. Modern integrated circuits are quite tolerant of "circulating currents" so if you're satisfied with the audio quality then no further action is necessary. Bob . . . --------------------------------------- ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) --------------------------------------- ________________________________ Message 6 _____________________________________ Time: 07:26:58 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: xponder ant mounting At 01:55 PM 6/6/2009, you wrote: > >Since I already installed a reinforcement plate into the floor of my >tailcone to mount my ground power receptacle, is there any reason >that I can't mount my transponder antenna into the same plate an >inch or two from the piper plug receptacle? > >Thanks in advance. I am loathe to drill holes into my skin without >checking first. I see no structural problems with it . . . One usually mounts the xponder antenna on the belly centerline. I presume your ground power jack structure is off to one side. I doubt that an off-center antenna location is any big deal. Bob . . . --------------------------------------- ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) --------------------------------------- ________________________________ Message 7 _____________________________________ Time: 08:42:42 AM PST US Subject: AeroElectric-List: RF interference fix From: Erich_Weaver@URSCorp.com Thanks for the response Bob. I have called GRT - they did not seem to be familiar with this problem. I am also a follower of the Vans Air Force list and multiple posts there have turned up only one other individual with similar fuel pressure symptoms, and I wasnt ever able to confirm that h is problem was RF related. This all seems strange to me as there are many RVs with similar equipment (SL-40 comm, GRT EFIS/EIS) and wiring (Z-13/8) t hat have my problem. Anyway, GRT suggested a ferrite filter , which I trie d without success. Looks like I may just have to live with this issue. Good to know that the noise I hear on my handheld will likely disappear by connecting it to ships antenna. I have a small device that allows switching between two radios on a single antenna, but have not yet hook ed it up - on my to do list. thanks again Erich ------------------------------------------------------------------------------------- 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.