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tony roberts wrote:
To respond to the questions that were in some responses, if a fly a 360 the needle tracks the NDB if I am near it, but not if I am several miles away. I had some similar problems with the Narco ADF 841. It wouldn't lock onto anything more than a few miles away until the radio had been on for an hour or so. I sent it in for repair, the shop tested it and replaced two capacitors, and now it works perfectly. A one-hour bench-test of your ADF at a good avionics shop is probably the cheapest place to start -- just yank it out yourself and mail or drive it in. You're right that the problem could be the antenna or connections, but it will take longer to test those (and most shops don't even have proper equipment for ramp-testing an ADF antenna and cables the way they can ramp-test a VOR antenna and cables), so you might as well rule out the radio first: besides, you won't have to ground your plane while the radio's being tested, unless you need it for a specific IFR approach. All the best, David |
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On Tue, 11 May 2004 02:37:46 GMT, tony roberts
wrote: Thanks very much for all the advice. It looks as though loop antenna is most likely, with radio interference as the second most likely. I'll fly it with everything shut off to see if the problem persists, to help narrow it further. To respond to the questions that were in some responses, if a fly a 360 the needle tracks the NDB if I am near it, but not if I am several miles away. Nospam asked if my crab angle was 30 degrees. No. If the NDB were ahead of the nose the needle pointed at 330, regardless of whether the NDB was at 300 degrees or 40 degrees. Thanks again for all the advice - I'll post the solution when I have it Tony As has alrady been suggested it may be interference, since it works close to the NDB. You say ' the needle tracks the NDB if I am near' so have you listened to the audio out of the ADF receiver? Maybe you can identify some interference. Sounds like a similar problem, we had, which was due to alternator noise (a whining noise which varies with engine RPM). In our case an alternator decoupling capacitor had not been fitted with the replacement alternator which did not have an inbuilt suppressor. E-mail (Remove Space after pilot): pilot |
#13
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#14
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A fellow objected to my posting somewhat strongly as follows:
That's just not how ADF circuits typically work. I think you're making all this up. Otherwise, you'd understand how the "oscillators" work when they're commonly digital PLL's, and that if a receiver did alignment, it sure ain't gonna be due to "drifting tantalum caps," as if they are especially prone to do that in the first place. O.K. Chill suit "ON". I believe we are talking about 25 year old radios. There ain't no digital ANYTHING in there (except maybe some units that had digital LED segmented or incandescent segmented frequency displays and some simple CMOS gate packages to drive them). As I said, I don't repair radios for a living. Sorry if your opinion is different. If anyone can explain analog AM radio alignment and theory of operation in better laymen's terms, I'm all ears. However, the 3 folks I deal with that do repair old radios for a living report that, in their experience, tantalum caps ARE more prone to leakage/failure with age than other types (electrolytics, mylars, etc.). Your experience may be different. If anyone has actual testing and failure data, please chime in. A few titles in the "Maintenance" section for my ADF: * Oscillator Alignment * IF Alignment * Receiver Alignment * ADF alignment. Leaking caps are not the problem? Maybe, but the odds are they contribute to some problems. Maybe I was just on a streak when we had to replace several of them in my unit to get it to work properly. Sorry, one was actually shorted, not leaking. If the caps were not leaking, resistors drifting/burning, and transistors changing conductance across their junctions (all due to heat and age), why would any of this be necessary? Does it matter WHICH component type actually causes the most trouble? I think not. The fellow was asking why his receiver did not point correctly. I tried to relay the message that many of these old buzzards needed the equivalent of a "tune up" to get them working properly. The posting above suggests that I was trying to sell him some kind of deception. Not so. Making it up? Let's just say that my efforts may be imperfect in this case. I cannot be an expert in everything. Hell, I ain't an expert in ANYTHING that I can think of. I only fixed electronic gear for a couple of years, and that was a LOOOOONG time ago. I was not volunteering to fix his receiver. So, I have no duty to be spot on in any diagnosis or explanation of the theory of operation. I offered my limited experience with the caveat that this ain't my line of work any more. I merely suggested he get the thing fixed. Sorry if my imperfect explanation of the problem causes anyone heartburn. My advice was worth every penny he paid (BIG SILLY GRIN) Good Luck, Mike P.S. Post from another fellow on the thread: "I had some similar problems with the Narco ADF 841. It wouldn't lock onto anything more than a few miles away until the radio had been on for an hour or so. I sent it in for repair, the shop tested it and replaced two capacitors, and now it works perfectly." Please note the offending devices - capacitors, I believe. Won't work unless REALLY warmed up = LEAKING. Maybe I am not that crazy after all... __________________________________________________ _____________________________ Posted Via Uncensored-News.Com - Accounts Starting At $6.95 - http://www.uncensored-news.com The Worlds Uncensored News Source |
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