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#1
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ADF Problem
Hi
Today I was flying north and my ADF was tuned to an NDB. The needle pointed at 330 degrees (or 11 O'clock) until I reached the NDB, and then it swung until it pointed behind. I dialed up the next NDB and it pointed at 330 again until passage. And I dialed up another NDB - same indication - all of them wrong. On the return trip - same indications. It seems logical that the nav, ADF head and antenna are working because I get a reading on station passage, but other than that, if I am tuned to an NDB anywhere ahead of the aircraft the needle points at 11 O'clock. Any ideas? Thanks Tony -- Tony Roberts PP-ASEL VFR OTT Night Almost Instrument Cessna 172H C-GICE |
#2
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On Sun, 09 May 2004 05:43:35 GMT, tony roberts
wrote: Hi Today I was flying north and my ADF was tuned to an NDB. The needle pointed at 330 degrees (or 11 O'clock) until I reached the NDB, and then it swung until it pointed behind. I dialed up the next NDB and it pointed at 330 again until passage. And I dialed up another NDB - same indication - all of them wrong. On the return trip - same indications. It seems logical that the nav, ADF head and antenna are working because I get a reading on station passage, but other than that, if I am tuned to an NDB anywhere ahead of the aircraft the needle points at 11 O'clock. Any ideas? Thanks Tony What was your crab angle, 30deg? E-mail (Remove Space after pilot): pilot |
#3
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Tony,
An ADF is basically an AM radio receiver with some added circuitry that uses a special antenna that allows us to derive the direction of the signal. Many of these units use discrete (individual) electronic components, AND most of these units are quite old. Certain capacitors in these units shift their electronic values over time, causing changes in the circuitry's operation. Hence, they need to be realigned every now and then. If not, over time the value shift in some components may make the unit not tune a signal or will not point to the station at all. The difficulty is in finding a radio shop that has the tools and personnel to align your ADF. This is usually done in the airplane because the 2 antennas (loop and sense) need to be aligned and "trimmed" with the unit. So, you need to bring the airplane to the shop for best results. Depending on where you are located, this may not be easy. Take a look in Trade-a-Plane or other publications to see if there is a shop near you. As an alternate, you can ship the unit out. That may or may not solve the problem depending on the antennas in your plane. If they happen to be close to the values of the test antennas at the shop, it will work. If not, the unit may may not work at its peak performance. Maybe some radio repair person can comment on the criticality of the antenna adjustment. I do not have a whole lot of experience with radios. Good Luck, Mike tony roberts wrote: Hi Today I was flying north and my ADF was tuned to an NDB. The needle pointed at 330 degrees (or 11 O'clock) until I reached the NDB, and then it swung until it pointed behind. I dialed up the next NDB and it pointed at 330 again until passage. And I dialed up another NDB - same indication - all of them wrong. On the return trip - same indications. It seems logical that the nav, ADF head and antenna are working because I get a reading on station passage, but other than that, if I am tuned to an NDB anywhere ahead of the aircraft the needle points at 11 O'clock. Any ideas? Thanks Tony __________________________________________________ _____________________________ Posted Via Uncensored-News.Com - Accounts Starting At $6.95 - http://www.uncensored-news.com The Worlds Uncensored News Source |
#4
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tony roberts wrote:
It seems logical that the nav, ADF head and antenna are working because I get a reading on station passage, but other than that, if I am tuned to an NDB anywhere ahead of the aircraft the needle points at 11 O'clock. Any ideas? When you do a 360-degree turn, does the needle stay at 330 all the way around, or does it turn as the aircraft turns? All the best, David |
#5
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Sounds to me like the loop antenna or the circuitry associated with it is dead.
This leaves only the sense antenna to say "ahead" or "behind". Jose -- (for Email, make the obvious changes in my address) |
#6
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"Mike Spera" wrote:
... Many of these units use discrete (individual) electronic components, AND most of these units are quite old. Certain capacitors in these units shift their electronic values over time, causing changes in the circuitry's operation. Hence, they need to be realigned every now and then. Per three ADF service manuals I have, there actually isn't any alignment procedure to adjust pointer indication. You are correct in that the installation may need trimmed out, but for example in one ADF, you remove a mounting screw on the indicator unit and tweak something with a supplied tool. In another, you loosen and physically twist the goniometer (what magnetically makes the needle move). Those adj. are worth only a few degrees, though. If there's a combined loop/sense antenna, it may have active circuitry inside which can also have a defective component, but it may not be field repairable. However, cleanliness and security of the loop antenna connections is one thing to check in any case. Beyond that, some component(s) somewhere is likely defective if a 30-deg error. Fred F. |
#7
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tony roberts wrote:
Hi Today I was flying north and my ADF was tuned to an NDB. The needle pointed at 330 degrees (or 11 O'clock) until I reached the NDB, and then it swung until it pointed behind. I dialed up the next NDB and it pointed at 330 again until passage. And I dialed up another NDB - same indication - all of them wrong. On the return trip - same indications. It seems logical that the nav, ADF head and antenna are working because I get a reading on station passage, but other than that, if I am tuned to an NDB anywhere ahead of the aircraft the needle points at 11 O'clock. Any ideas? Thanks Tony Did you have any portable electronic devices with you that you haven't carried before? If so, could be interference. If not, then it sounds like your ADF is going bad. Matt |
#8
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"tony roberts" wrote in message ... Hi Today I was flying north and my ADF was tuned to an NDB. The needle pointed at 330 degrees (or 11 O'clock) until I reached the NDB, and then it swung until it pointed behind. I dialed up the next NDB and it pointed at 330 again until passage. And I dialed up another NDB - same indication - all of them wrong. On the return trip - same indications. It seems logical that the nav, ADF head and antenna are working because I get a reading on station passage, but other than that, if I am tuned to an NDB anywhere ahead of the aircraft the needle points at 11 O'clock. Any ideas? Thanks Tony -- Tony Roberts PP-ASEL VFR OTT Night Almost Instrument Cessna 172H C-GICE I had a remarkably similar problem with an old Bendix unit. It turned out to be a short inside a connector, grounding one point of the loop aerial. (The connector had been put together with no washer under one of the screws holding the body and the slight extra projection had brought the screw in contact with a sleeved soldered terminal pin and over the years it had rubbed its way through the sleeve until it shorted!) I suggest you carefully check everything on the loop antenna circuitry outside the unit before sending it off for checking. Mike |
#9
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I had a similar problem. In my case, the needle would always point at 60 degrees until I was on top of the NDB then the needle would "seek" the station. Once I got beyond 2-3 miles from the NDB, it would go back to 60 degrees. I later determined that it only happened when the strobes were on. Come to find out, the power supply for the right strobe (located in the front of the right wing) was leaking interference. The ADF seeked the interference unless the NDB signal was very strong. I suspect was you have a similar problem. It should not be much of a problem for a radio shop to figure it out. Muncie (MIE) Indiana found my problem in about 15 minutes. Kevin Chandler |
#10
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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 -- Tony Roberts PP-ASEL VFR OTT Night Almost Instrument Cessna 172H C-GICE |
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