---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 10/03/05: 19 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:28 AM - (bob noffs) 2. 04:28 AM - Re: Re: Why are wire strands tinned ? (Ken) 3. 05:57 AM - Re: (Robert L. Nuckolls, III) 4. 08:34 AM - Re: capacitor and music jack help needed (Eric M. Jones) 5. 08:34 AM - Re: (Roger Evenson) 6. 09:00 AM - Vacuum pad alternator options for Rotax (Jon Goguen) 7. 09:17 AM - Re: Vacuum pad alternator options for Rotax (Bill Denton) 8. 10:47 AM - Re: Vacuum pad alternator options for Rotax (Jon Goguen) 9. 11:28 AM - Re: XCOM 760 (Eric M. Jones) 10. 11:31 AM - 5vDC Power Supply... (Greg Campbell) 11. 01:53 PM - New to List (Will N. Stevenson) 12. 02:18 PM - Re: Xcom 760 Redux (Eric M. Jones) 13. 03:32 PM - Re: Re: Xcom 760 Redux (Matt Prather) 14. 04:16 PM - Re: (Robert L. Nuckolls, III) 15. 04:21 PM - Re: Re: capacitor and music jack help needed (Robert L. Nuckolls, III) 16. 04:22 PM - Re: New to List (Eric M. Jones) 17. 04:25 PM - Re: Re: XCOM 760 (Robert L. Nuckolls, III) 18. 07:05 PM - Re: New to List (rv-9a-online) 19. 08:50 PM - Fox tails anyone? (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 04:28:51 AM PST US From: "bob noffs" Subject: AeroElectric-List: --> AeroElectric-List message posted by: "bob noffs" hi bob, can i benefit from using your audio isolation amp board with just a transceiver and headsets[ no music system] bob noffs, woodruff, wi ________________________________ Message 2 _____________________________________ Time: 04:28:51 AM PST US From: Ken Subject: Re: AeroElectric-List: Re: Why are wire strands tinned ? --> AeroElectric-List message posted by: Ken As someone who has occasionally worked on 10+ year old cars in the rust/salt belt, I would agree that there should be a "special place" for manufacturers who install untinned wire in automobiles as well. I've seen every strand badly corroded for the entire length of the wire. Presumably moisture wicks its way many feet up the wires. Ken >An airplane is typically in a much more benign environment unless it is >based near salt water. Nonetheless, I think tinned wire is a real good >idea. > > ________________________________ Message 3 _____________________________________ Time: 05:57:22 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" At 06:23 AM 10/3/2005 -0500, you wrote: >--> AeroElectric-List message posted by: "bob noffs" > >hi bob, can i benefit from using your audio isolation amp board with just >a transceiver and headsets[ no music system] > bob noffs, woodruff, wi Very simple audio systems are illustrated in Chapter 18: http://aeroelectric.com/articles/Rev11/18Audio_R11.pdf . . . specifically in Figure 18-7 and associated text. An airplane with one or two sources of audio does not benefit from an isolation amplifier. Bob . . . ________________________________ Message 4 _____________________________________ Time: 08:34:09 AM PST US From: "Eric M. Jones" Subject: AeroElectric-List: Re: capacitor and music jack help needed --> AeroElectric-List message posted by: "Eric M. Jones" --> AeroElectric-List message posted by: luckymacy@comcast.net (lucky) >What if I just got something like the one at >http://www.sphere.bc.ca/test/inductors.html >Fair Rite Snap-It RFI Ferrite Suppressors....Fits wires/bundles up to >10mm/0.390 >inch in diameter, easily opens and snaps shut, fantastic for quenching >EMI/RFI >emissions from already existing equipment, power cords, cables, and >connections. >Type 0443167251, approx. 225 ohms impedance at 100Mhz, very efficient and >inexpensive emission solution. >Seems like it would be easy to install and remove if it didn't work. >Lucky Lucky, It won't do anything for you. The snap-on ferrites are good for very high frequencies only--like MegaHertz and GigaHertz. We need a "Very Low Pass Filter" The thing we need for kiloHertz noise is an inductor that is a substantial physical size and in the milliHenry range. The capacitors we need are also much smaller than 22kuF. There are a zillion prescriptions for noise filters. Radio Shack used to carry suitable chokes. But the choices are slimmer now. If you know a little about the subject you can design filters with many available online calculators like the excellent free one from www.nuhertz.com . The newest noise filters are "active" filters, which means they have electronics that vary the filter response as needed. I recommend getting noise filters from J.C. Whitney or Crutchfield or any big car-audio place. They have good ones for short money. Just Google "noise filters". Remember-- you are way ahead if you stop the noise at the source. My airplane will have a high current B+ noise filter near the alternator, and one or more low current devices on the "avionics bus" or associated with radios and intercoms wirings. Regards, Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge MA 01550-2705 (508) 764-2072 Ring the bells that still can ring Forget your perfect offering There is a crack in everything That's how the light gets in. --Leonard Cohen ________________________________ Message 5 _____________________________________ Time: 08:34:21 AM PST US From: "Roger Evenson" Subject: Re: AeroElectric-List: --> AeroElectric-List message posted by: "Roger Evenson" How about three sources of audio? Will three sources work with resistors only and no isolation amp? ----- Original Message ----- From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: > --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" > > > At 06:23 AM 10/3/2005 -0500, you wrote: > >>--> AeroElectric-List message posted by: "bob noffs" >> >>hi bob, can i benefit from using your audio isolation amp board with just >>a transceiver and headsets[ no music system] >> bob noffs, woodruff, wi > > > Very simple audio systems are illustrated in Chapter 18: > > http://aeroelectric.com/articles/Rev11/18Audio_R11.pdf > > . . . specifically in Figure 18-7 and associated text. > An airplane with one or two sources of audio does not > benefit from an isolation amplifier. > > Bob . . . > > > ________________________________ Message 6 _____________________________________ Time: 09:00:18 AM PST US From: Jon Goguen Subject: AeroElectric-List: Vacuum pad alternator options for Rotax --> AeroElectric-List message posted by: Jon Goguen Does anyone have experience with the modified Densei alternators that mount on the vacuum pad of Rotax engines (esp. 912S) and are sold by Flight Crafters, Lockwood aviation, and perhaps some others? As I understand it, these are essentially standard automotive devices with internal regulation mechanically modified to fit the vacuum pad. I'm particularly interested in their current capability. I'm told by the vendors that they'll provide 40 amps at 2800 rpm, a speed compatible with the 912S vacuum pad rpm in cruise. I had originally intended to use the B&C Systems SD20, but--as pointed out to me by Paul Wilson on the list and confirmed by B&C--the output of the SD20 is only 12 amps due to the low rpm at the pad. Lockwood says the Densei alternative is especially popular in Europas. Anyone know how well these things work in real life? Thanks! Jon Jon Goguen jon.goguen@umassmed.edu Central Massachusetts Kitfox Series V Rotax 912S / N456JG (reserved) Complete except for electrics and avionics ________________________________ Message 7 _____________________________________ Time: 09:17:33 AM PST US From: "Bill Denton" Subject: RE: AeroElectric-List: Vacuum pad alternator options for Rotax --> AeroElectric-List message posted by: "Bill Denton" Rotax also offers an external alternator for the 912; part number: 887254. -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com]On Behalf Of Jon Goguen Subject: AeroElectric-List: Vacuum pad alternator options for Rotax --> AeroElectric-List message posted by: Jon Goguen Does anyone have experience with the modified Densei alternators that mount on the vacuum pad of Rotax engines (esp. 912S) and are sold by Flight Crafters, Lockwood aviation, and perhaps some others? As I understand it, these are essentially standard automotive devices with internal regulation mechanically modified to fit the vacuum pad. I'm particularly interested in their current capability. I'm told by the vendors that they'll provide 40 amps at 2800 rpm, a speed compatible with the 912S vacuum pad rpm in cruise. I had originally intended to use the B&C Systems SD20, but--as pointed out to me by Paul Wilson on the list and confirmed by B&C--the output of the SD20 is only 12 amps due to the low rpm at the pad. Lockwood says the Densei alternative is especially popular in Europas. Anyone know how well these things work in real life? Thanks! Jon Jon Goguen jon.goguen@umassmed.edu Central Massachusetts Kitfox Series V Rotax 912S / N456JG (reserved) Complete except for electrics and avionics ________________________________ Message 8 _____________________________________ Time: 10:47:27 AM PST US From: Jon Goguen Subject: Re: AeroElectric-List: Vacuum pad alternator options for Rotax --> AeroElectric-List message posted by: Jon Goguen Bill, Thanks. Unfortunately, that option doesn't fit under the cowl without a lot of modification. Regards, Jon Jon D. Goguen, Ph. D. Department of Molecular Genetics and Microbiology University of Massachusetts Medical School 55 Lake Avenue North Worcester, MA 01655 Phone 508.856.2490 Fax 508.856.5920 On Oct 3, 2005, at 12:16 PM, Bill Denton wrote: > --> AeroElectric-List message posted by: "Bill Denton" > > > Rotax also offers an external alternator for the 912; part number: > 887254. > > > -----Original Message----- > From: owner-aeroelectric-list-server@matronics.com > [mailto:owner-aeroelectric-list-server@matronics.com]On Behalf Of Jon > Goguen > To: aeroelectric-list@matronics.com > Subject: AeroElectric-List: Vacuum pad alternator options for Rotax > > > --> AeroElectric-List message posted by: Jon Goguen > > > Does anyone have experience with the modified Densei alternators that > mount on the vacuum pad of Rotax engines (esp. 912S) and are sold by > Flight Crafters, Lockwood aviation, and perhaps some others? As I > understand it, these are essentially standard automotive devices with > internal regulation mechanically modified to fit the vacuum pad. I'm > particularly interested in their current capability. I'm told by the > vendors that they'll provide 40 amps at 2800 rpm, a speed compatible > with the 912S vacuum pad rpm in cruise. I had originally intended to > use the B&C Systems SD20, but--as pointed out to me by Paul Wilson on > the list and confirmed by B&C--the output of the SD20 is only 12 amps > due to the low rpm at the pad. Lockwood says the Densei alternative is > especially popular in Europas. Anyone know how well these things work > in real life? > > Thanks! > > Jon > > Jon Goguen > jon.goguen@umassmed.edu > Central Massachusetts > Kitfox Series V Rotax 912S / N456JG (reserved) > Complete except for electrics and avionics > > ________________________________ Message 9 _____________________________________ Time: 11:28:11 AM PST US From: "Eric M. Jones" Subject: AeroElectric-List: Re: XCOM 760 --> AeroElectric-List message posted by: "Eric M. Jones" (do not archive) XCOM has refused to send me schematic of the power input section of the XCOM 760 radio. What are they hiding??? Regards, Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge MA 01550-2705 (508) 764-2072 ________________________________ Message 10 ____________________________________ Time: 11:31:58 AM PST US From: "Greg Campbell" Subject: AeroElectric-List: 5vDC Power Supply... --> AeroElectric-List message posted by: "Greg Campbell" Hi, I'm going to wire in a Garmin GPS 18 5Hz backup GPS receiver to my EFIS. http://www.garmin.com/products/gps185hz/ and it requires 4.0 to 5.5 vdc input, drawing 65 mA @ 5vdc. http://www.garmin.com/products/gps185hz/spec.html For initial testing, I'm using 4 AA NiCd's (in series, 4.8vDC) rated at 2300mAh each. This is fine as long as I remember to charge them up, and turn the GPS off between uses. (It's just a backup GPS Input for the EFIS & Autopilot). For the final installation, I'd like to power it off 12vdc Ships Power. I bought a 5vDC "Fixed Voltage Regulator" that supplies up to 1 Amp. http://www.radioshack.com/product.asp?catalog%5FnameCTLG&product%5Fid276-1770 The one I got didn't have any instructions, and there is no spec sheet at www.RadioShack.com Do these typically require external resistors? Heat sinks? etc ? Any advice on wiring up the voltage regulator? Then, to make things a bit fancier - I was hoping to run it from Ships Power AND have a small AA or AAA battery backup pack for the GPS receiver. The "ideal" battery backup system would: 1) Automatically charge up the NiCd's whenever the ship's power is ON 2) Not "overcharge" the NiCds or charge them at more than about 0.8 Amps. 3) Automatically power the GPS from the NiCds whenever the 5vDC power is "lost" 4) Automatically shut off the GPS after 6 to 8 hours so the NiCds don't drain completely. Any advice on wiring up a simple and elegant backup battery? Thanks in advance, Greg ________________________________ Message 11 ____________________________________ Time: 01:53:14 PM PST US From: "Will N. Stevenson" Subject: AeroElectric-List: New to List --> AeroElectric-List message posted by: "Will N. Stevenson" Eric, I'm new on this list and am overjoyed to find both you and Bob as sources of future advice. I am building an experimental plane and plan on using your Fatwire to move my battery aft in order to eliminate the tailcone ballast weight req'd when the battery is hung in its usual place on the firewall. I bought a copy of Bob's Aeroelectric Connection and have begun the journey to electrical literacy, so that I can install an all-electric panel in the aircraft myself. You mentioned "My airplane will have.......,etc." --I wanted to ask you--what plane are you interested in or building? Also, can you recommend any reading for a person who wants to self-teach avionics and aircraft electrical stuff other than Bob's book? I already have a good background in basic automotive electrical troubleshooting but want to go further. Thanks, Will > My airplane will have a high current B+ noise filter near the alternator, > and > one or more low current devices on the "avionics bus" or associated with > radios and intercoms wirings. > Regards, > Eric M. Jones > www.PerihelionDesign.com ________________________________ Message 12 ____________________________________ Time: 02:18:03 PM PST US From: "Eric M. Jones" Subject: AeroElectric-List: Re: Xcom 760 Redux --> AeroElectric-List message posted by: "Eric M. Jones" (do not archive) Naw..shucks....the very nice people at XCOM came around and sent me their schematic. I really appreciate it and give them a gold star for their service. The internal design of the device is first rate. Ken Luxford disclosed an important point: XCOM writes--- There seems to be some confusion regarding the requirement for the 22kuF capacitor. This is a Rotax requirement and NOT necessarily a requirement for the XCOM. We have seen multiple Rotax installations here which have not had the recommended( by Rotax) 22kuF capacitor fitted. The Rotax regulator appears to be quite noisy without it. In some circumstances we have also seen cases where high current strobes and similar have caused some fairly nasty transients on the supply. In these cases, a fairly large capacitor on the supply line can be advantageous. Regards Ken Luxford Regards, Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge MA 01550-2705 (508) 764-2072 "Hey, it ain'tt rocket surgery!" --anonymous ________________________________ Message 13 ____________________________________ Time: 03:32:51 PM PST US Subject: Re: AeroElectric-List: Re: Xcom 760 Redux From: "Matt Prather" --> AeroElectric-List message posted by: "Matt Prather" This makes perfect sense and completes the picture. Thanks for bugging them about this Eric. Regards, Matt- > --> AeroElectric-List message posted by: "Eric M. Jones" > > > (do not archive) > > Naw..shucks....the very nice people at XCOM came around and sent me > their schematic. I really appreciate it and give them a gold star for > their service. > > The internal design of the device is first rate. Ken Luxford disclosed > an important point: > > XCOM writes--- > > There seems to be some confusion regarding the requirement for the 22kuF > capacitor. This is a Rotax requirement and NOT necessarily a requirement > for the XCOM. We have seen multiple Rotax installations here which have > not had the recommended( by Rotax) 22kuF capacitor fitted. The Rotax > regulator appears to be quite noisy without it. In some circumstances > we have also seen cases where high current strobes and similar have > caused some fairly nasty transients on the supply. In these cases, a > fairly large capacitor on the supply line can be advantageous. > > Regards > Ken Luxford > > Regards, > Eric M. Jones > www.PerihelionDesign.com > 113 Brentwood Drive > Southbridge MA 01550-2705 > (508) 764-2072 > > "Hey, it ain'tt rocket surgery!" > --anonymous > > ________________________________ Message 14 ____________________________________ Time: 04:16:08 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" At 08:33 AM 10/3/2005 -0700, you wrote: >--> AeroElectric-List message posted by: "Roger Evenson" > > >How about three sources of audio? Will three sources work with resistors >only and no isolation amp? Probably. Try it and see. You can always add the iso-amp later if the resistor-mix method doesn't work for you. Bob . . . ________________________________ Message 15 ____________________________________ Time: 04:21:17 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: capacitor and music jack help needed --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" At 11:46 AM 10/2/2005 -0600, you wrote: >--> AeroElectric-List message posted by: "Matt Prather" > >The thing that is slightly frustrating about this whole discussion is that >when you buy the XCOM (or whatever else), presumably you are buying a comm >transceiver that is designed to be installed in an aircraft. And that it >will be wired into the aircraft power buss. Why the heck wasn't the radio >designed to perform correctly in that environment (without adding >additional "stuff")?? I'm pretty certain that the XCOM (like it's predecessor in the market - Microair 760) will work just fine on typical light aircraft bus fed by an automotive alternator. Many ultra-light owners like these tiny radios too and they're almost always fitted with PM alternators that are NOISY without additional filtering. Check the instructions carefully, is the large cap ALWAYS recommended or a suggested solution in case you do have noise? Unless you're flying behind a Rotax, you won't need the cap. If you are flying a PM alternator, then I presume one will begin with one of the appropriate Z-figures where this capacitor is always included. The XCOM is not the only accessory that will appreciate the presence of the extra filtering. Bob . . . ________________________________ Message 16 ____________________________________ Time: 04:22:34 PM PST US From: "Eric M. Jones" Subject: AeroElectric-List: Re: New to List --> AeroElectric-List message posted by: "Eric M. Jones" --> AeroElectric-List message posted by: "Will N. Stevenson" >Eric, >I'm new on this list and am overjoyed to find both you and Bob as sources >of >future advice. I am building an experimental plane and plan on using your >Fatwire to move my battery aft in order to eliminate the tailcone ballast >weight req'd when the battery is hung in its usual place on the firewall. >I >bought a copy of Bob's Aeroelectric Connection and have begun the journey >to >electrical literacy, so that I can install an all-electric panel in the >aircraft myself. >You mentioned "My airplane will have.......,etc." --I wanted to ask >you--what plane are you interested in or building? Also, can you recommend >any reading for a person who wants to self-teach avionics and aircraft >electrical stuff other than Bob's book? I already have a good background >in >basic automotive electrical troubleshooting but want to go further. Thanks, >Will Welcome Will, I am building Glastar N5EJ with a Sube 2.5L and I intend to finish it this century. Starting a business has taken funds and time from the building. You didn't say what you're building. (?) (do not archive) Regards, Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge MA 01550-2705 (508) 764-2072 "The man who carries a cat by the tail learns something that can be learned in no other way." - Mark Twain ________________________________ Message 17 ____________________________________ Time: 04:25:06 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: XCOM 760 --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" At 02:27 PM 10/3/2005 -0400, you wrote: >--> AeroElectric-List message posted by: "Eric M. Jones" > >(do not archive) > >XCOM has refused to send me schematic of the power input section of the XCOM >760 radio. > >What are they hiding??? King, Narco, and most other folks wont send them out either. If you're an authorized service station and pay money for service manuals, you get all the schematics. They're not "hiding" anything, just complying with what has been an industry practice since day-one. I work for a BIG user of products from the major suppliers and I don't get schematics without a lot of bother (I go to their local service shop and borrow them to copy). Bob . . . ________________________________ Message 18 ____________________________________ Time: 07:05:51 PM PST US From: rv-9a-online Subject: Re: AeroElectric-List: New to List --> AeroElectric-List message posted by: rv-9a-online Will: There is a series of presentations on aircraft electrical system design at http://b4.ca/raa_85/story/index.html . These presentation were designed for the non-EE types who have to build or maintain their own aircraft. They are not the definitive training course, but may be of use as an introduction in conjuction with Bob's book (which is referenced along with some other publications). Vern Little -9A in the paint shop. Will N. Stevenson wrote: >--> AeroElectric-List message posted by: "Will N. Stevenson" > >Eric, >I'm new on this list and am overjoyed to find both you and Bob as sources of >future advice. I am building an experimental plane and plan on using your >Fatwire to move my battery aft in order to eliminate the tailcone ballast >weight req'd when the battery is hung in its usual place on the firewall. I >bought a copy of Bob's Aeroelectric Connection and have begun the journey to >electrical literacy, so that I can install an all-electric panel in the >aircraft myself. > >You mentioned "My airplane will have.......,etc." --I wanted to ask >you--what plane are you interested in or building? Also, can you recommend >any reading for a person who wants to self-teach avionics and aircraft >electrical stuff other than Bob's book? I already have a good background in >basic automotive electrical troubleshooting but want to go further. > >Thanks, >Will > > > > >>My airplane will have a high current B+ noise filter near the alternator, >>and >>one or more low current devices on the "avionics bus" or associated with >>radios and intercoms wirings. >> >> > > > >>Regards, >>Eric M. Jones >>www.PerihelionDesign.com >> >> > > > > ________________________________ Message 19 ____________________________________ Time: 08:50:16 PM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Fox tails anyone? --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" > > > My airplane will have a high current B+ noise filter near the alternator, > > and one or more low current devices on the "avionics bus" or associated > with > > radios and intercoms wirings. A few weeks ago, we had some discussions about the value of applying certain prophylactic measures to the installation of devices in light aircraft with the notion that the additions were of some value in standing off spikes and noises (their intended purpose) and that a generous sprinkling of these devices about the system (while not harmful) were recommended just to make sure the offending stimulus, should it manifest itself, would be managed with dispatch and aplomb. In the very early days of publishing the 'Connection, a Longez builder called me one evening to explain that, "I've wired the whole airplane with shielded wire. I filtered the fuel pumps, alternator, mags and defog blower. What else do I need? I was taken aback by his story and asked, "Gee, I don't know. What kind of a noise problem do you have?" "Oh, no problem", replies he, "I haven't flown the airplane yet but I'm just trying to be sure that noise isn't going to be a problem." Similarly, I've noted that certain purveyors of quick-install bus and switch products are fond of citing extra noise filters and/or spike catchers as built in features worthy of elevating their product's return on investment. Just for grins, I went out to the driveway with trusty 'scope and took this picture off the cigar lighter in my '95 Safari with a 90A alternator, all loads turned on, engine over 2000 RPM so that the bus voltage was over 14.0 volts: http://www.aeroelectric.com/Pictures/Safari_Bus_Noise_1.gif Note that the major noise components are bounded by pk-pk excursions on the order of 300 millivolts. There were some narrow, higher voltage transients which I expanded out in this picture: http://www.aeroelectric.com/Pictures/Safari_Bus_Noise_2.gif Hmmm . . . about a millisecond wide and excursions on the order of 600-800 millivolts. Interestingly enough, the general appearance of these noises did not seem to be affected much by what was turned on or by engine RPM. It was difficult to see what I hoped to identify as alternator ripple . . . typically 1.5 volts peak-to-peak from an unfiltered 3-phase rectifier. The reason that these noise are so small is because the system is already fitted with a very effective filter called a BATTERY. In the spam can business, we tell prospective suppliers of electro-whizzies to EXPECT and be TOLERANT of noises as described in: http://www.aeroelectric.com/Pictures/MSTD704_28V_Noise.jpg This is for a 28v system, we're working with a 14v system so the values are cut in half. In the frequency range of 1000 to 8000 Hz, expect noises in a 14v system of 0.5 vrms or 1.5 v pk-pk. Outside this band, the energy of expected noises falls off at 10 to 40 db per decade. At first blush, my '95 Safari's electrical system complies with the spirit and intent of Mil-Std-704 for allowable noise. In fact, it's much quieter. I can tell you that unless the battery is VERY soggy, light aircraft with automotive alternators have similar noise energies. Now, let's consider a conversation of a few hours ago wherein a builder was understandably miffed by the need to add external noise filtering in the form a hefty capacitor as recommended by the radio's manufacturer. I suggested that this requirement made sense for small aircraft with single-phase, PM alternators where the rectified output was VERY trashy. Most accessories would benefit from having the large capacitor added to the battery in terms of overall system noise reduction. Indeed, this capacitor was shown in all Z-figures illustrating PM alternator installations. I'm quite certain that makers of the XCOM (along with the vast majority of professional suppliers to industries featuring DC powered vehicles) fully understand the nature of the world they're expected to live in as do all of RACs suppliers by specification. The idea that there is benefit to adding extra filtering . . . just for good measure . . . does not drive toward the elegant solution. It drives up parts count concentrated in the supply line to a suite of accessories and probably adds no operational value except to accommodate poorly designed products that need the extra filtering. In the later case, it's more prudent to add needed filtering to that one system only so as to avoid adding unnecessary complexity in series with systems that never needed extra filtering in the first place. I recall a crusty ol' mechanic I worked beside in one of my earliest jobs in two-way radio. He had a fox-tail on his car's radio antenna. He called it his "go fast ornament". When I inquired about its title, he offered that once the fox tail was added to the antenna, it could be observed increase the speed of his car. Since the antenna laid back so much further the car was obviously going faster. The siren song of gee-whiz features is seductive. Folks at OSH sell all kinds of products with ad hype bolstered by claims having no or poor foundations in practice or physics. Any time a claimed feature increases parts count without adding operational value, the elegance of design is degraded. Additionally weight, volume, and cost of ownership go up. We have lots of filters and fixes applied to various systems and devices in our production aircraft . . . all of which are incorporated to mitigate a known performance problem. We work up to the boundaries of DO160/MS704 but no further. This judicial application of remedy in response to real problems avoids unnecessary and reliability reducing over-design. It also avoids addition of no-value-added "go fast" features. One's risk of encountering a noise problem after good practice for grounding and manufacturer's recommendations for shielding. Any residual noise problems will be relatively easy to find and fix and will probably demonstrate a design flaw that the "fox-tail" wouldn't have helped with anyhow. Bob . . .