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#11
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DME operates by transmitting to and receiving paired pulses from the
ground station. The transmitter in the aircraft sends out very narrow pulses at a frequency of about 1,000 MHz. These signals are received at the ground station and trigger a second transmission on a different frequency. These reply pulses are sensed by timing circuits in the aircraft's receiver that measure the elapsed time between transmission and reception. Electronic circuits within the radio convert this measurement to electrical signals that operate the distance and ground speed indicators. Jon Kraus '79 Mooney 201 443H @ UMP ..Blueskies. wrote: wrote in message ... : On Fri, 04 Aug 2006 09:37:44 -0400, Jonathan Goodish : wrote: : : In article .com, : "Jay Honeck" wrote: : http://www.scn.org/~bk269/gps.html : : This is an interesting site that explains why some pilots (seemingly : mostly running Garmin-brand portable GPS units) are having trouble with : losing satellite lock. : : : We had a problem in our PA28 with a Skymap II (panel mounted GPS) when : using an antenna on the top of the instrument panel. The culprit was : the Narco IDME 825 and depended which frequency the DME was tuned. The : DME transmitter blocked the GPS receiver. There was a considerable : improvement when we fitted an external roof antenna. We have now : fitted a Skymap IIIc GPS which is understand has a better receiver : and so far appears ok. Didn't know DME transmitted... |
#12
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".Blueskies." wrote in message
... Excellent, thanks! In addition to Jon's nice explanation of DME, I'd like to point out that because DME is an active receive-and-reply system, it can get saturated when too many aircraft are using the same DME site. A pilot using DME in busy airspace should keep this in mind, in case some funny numbers start getting spit out, or the DME just stops giving any indications. I admit, I've never actually seen this happen, but it is theoretically possible. Pete |
#13
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In article ,
"Peter Duniho" wrote: In addition to Jon's nice explanation of DME, I'd like to point out that because DME is an active receive-and-reply system, it can get saturated when too many aircraft are using the same DME site. A pilot using DME in busy airspace should keep this in mind, in case some funny numbers start getting spit out, or the DME just stops giving any indications. I admit, I've never actually seen this happen, but it is theoretically possible. Interesting. I hadn't thought about the interrogator before. But It's more likely that the ground station will reduce the sensitivity to the point that it doesn't transmit that many replies - thereby reducing the probability the DME will be listening to a reply intended for someone else. For a DME interrogator that already acquired the ground station and is tracking, it's extremely unlikely that its tracking algorithm will drift off. Remember that the interrogations are psuedorandom, there are only 30 interrogations per second (IIRC), and they are short. -- Bob Noel Looking for a sig the lawyers will hate |
#14
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"Bob Noel" wrote in message
... Interesting. I hadn't thought about the interrogator before. But It's more likely that the ground station will reduce the sensitivity to the point that it doesn't transmit that many replies - thereby reducing the probability the DME will be listening to a reply intended for someone else. That would cause the DME in the airplane to stop providing DME information, which is one of the consequences I mentioned. I admit, I wasn't precise about which "DME" would stop giving nay indications...it's the one in the airplane I was talking about. For a DME interrogator that already acquired the ground station and is tracking, it's extremely unlikely that its tracking algorithm will drift off. Remember that the interrogations are psuedorandom, there are only 30 interrogations per second (IIRC), and they are short. I agree it's less likely you'll get erroneous data from the DME. It'd be a pretty rare situation in which that happens, assuming it has ever happened at all anywhere. My main point is just that pilots should be aware of the limitations of DME (I guess we could mention slant-range here too, but I think we were just talking about the radio signal itself? I've lost track ![]() Pete |
#15
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On Fri, 04 Aug 2006 22:14:39 GMT, ".Blueskies."
wrote: wrote in message ... : On Fri, 04 Aug 2006 09:37:44 -0400, Jonathan Goodish : wrote: : : In article .com, : "Jay Honeck" wrote: : http://www.scn.org/~bk269/gps.html : : This is an interesting site that explains why some pilots (seemingly : mostly running Garmin-brand portable GPS units) are having trouble with : losing satellite lock. : : : We had a problem in our PA28 with a Skymap II (panel mounted GPS) when : using an antenna on the top of the instrument panel. The culprit was : the Narco IDME 825 and depended which frequency the DME was tuned. The : DME transmitter blocked the GPS receiver. There was a considerable : improvement when we fitted an external roof antenna. We have now : fitted a Skymap IIIc GPS which is understand has a better receiver : and so far appears ok. Didn't know DME transmitted... Yes it does as nicely explained by Jon. I should have pur IDME 891 (not 825) and it transmitts with 25 watts. |
#16
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On Fri, 4 Aug 2006 16:29:56 -0700, "Peter Duniho"
wrote: ".Blueskies." wrote in message m... Excellent, thanks! In addition to Jon's nice explanation of DME, I'd like to point out that because DME is an active receive-and-reply system, it can get saturated when too many aircraft are using the same DME site. A pilot using DME in busy airspace should keep this in mind, in case some funny numbers start getting spit out, or the DME just stops giving any indications. I admit, I've never actually seen this happen, but it is theoretically possible. Pete I can't remember the numbers but a VOR/DME will accept a large number of aircraft before it saturates. Some Terminal DME's are only capable of supporting about 5 or 10 aircraft (only needed for an instrument approach anyway). Since they are short range it's not usually a problem. I have more, than once, lost DME but not usually for long (less than a minute). Mostly at longer range where other aircraft are probably nearer the DME and a stronger signal than me. |
#17
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![]() mbremer216 wrote: I have a full Narco stack in my Cherokee My deepest sympathies. ![]() -robert |
#18
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![]() "Robert M. Gary" wrote in message ups.com... mbremer216 wrote: I have a full Narco stack in my Cherokee My deepest sympathies. ![]() -robert LOL! For the Narcos or the Cherokee -- or both... That was cruel, I'll take it back. Hehehehe.... |
#19
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I don't know why...I've never had a lick of trouble out of any of it.
Mike "Robert M. Gary" wrote in message ups.com... mbremer216 wrote: I have a full Narco stack in my Cherokee My deepest sympathies. ![]() -robert |
#20
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I don't know why...I've never had a lick of trouble out of any of it.
Atlas has two Narco coms, a Narco DME, and two Narco GS/VORs. All work perfectly, all the time. I've not quite figured out where the anti-Narco sentiment come from, but it's almost as insidious as the anti-Microsoft attitudes out there. -- Jay Honeck Iowa City, IA Pathfinder N56993 www.AlexisParkInn.com "Your Aviation Destination" |
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