Air Traffic Communication question

Discussion in 'General Electronics Chat' started by Shelton, Apr 15, 2008.

  1. Shelton

    Thread Starter Member

    Mar 13, 2008
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    Hi All

    Sorry for a very stupid question - I understand that Air Traffic Communication is done using AM. Now this is usually in the band 110-130Mhz - now what I want to know is - is this actually FM as the carrier because I thought FM starts at about 88Mhz - so is it FM carrier and AM communication - so basically we are talking about ATC as FM ?

    Regards,
    Shelton.
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Modulation scheme doesn't care about frequency. Frequency doesn't care about modulation scheme. The various frequency bands were assigned by bureaucrats who in turn were hired by politicians. Any frequency of signal can have any modulation scheme. Whether the combination is legal or not is another matter.
     
  3. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
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    well, in FM the modulation cant be greater than the carrier, so they do care about each other.

    i think the OP is confused about what AM and FM really is. "FM" is not a carrier, it's a type of modulation.
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    ATC communication uses the frequencies from about 110 to 136 MHz with AM Modulation. The lower portion is used for navigation aids like VORs. Those use phase modulation techniques so the CDI in the aircraft can tell weather it is to the left or right of a particular track to the VOR. VORs are usually in the range 110 to 118 Mhz.

    Voice communication with control towers is generally in the range 118 to 126 Mhz. Approach, Departure, ARTCC frequencies are generally 126 to 135. ATIS frequencies are generally at the top of the range. The use of AM modulation on those frequencies was due to the requirements of simplicity in the early days of aviation when radios were made with vacuum tubes. An AM transceiver is a much simpler animal than an FM transceiver by a wide margin.

    What surprises me is that aviation never made the switch to single sideband except for HF communication by long overwater flights.
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    Aircraft don't use FM because an FM receiver has a "capture ratio" where it receives only the stronger of two signals. Then during a normal traffic control conversation another airplane won't be heard interrupting and saying "HELP, I can't slow down so get out of my way". AM signals mix together so both will be heard.
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    To which the traffic controller would respond with appropriate calm...
    Code ( (Unknown Language)):
    1.  
    2. "Cesna 4014Q..Do you wish to declare an emergency?"
    3.  
    And responding as all good pilots would after their initial contact with Air Traffic Control using the last two or three letters and digits of their callsign
    Code ( (Unknown Language)):
    1.  
    2. "That's affirmative!...4Q!"
    3.  
     
  7. Shelton

    Thread Starter Member

    Mar 13, 2008
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    0
    OK That explains why they dont use FM - always wondered why they never converted to FM.
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    During a thunderstorm AM won't be useable. Maybe then they switch to FM.
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    Even if they (ATC) could I'm pretty sure the aircraft radios can't. At least they couldn't the last time I was a PIC (pilot in command).
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
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    Yankee 39er, say all after skraak. Be aware your squelch is broken.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Papabravo started it. :D

    Actually, I was just looking for the very last quote - but the rest were so good I couldn't help myself ;)

    From an unknown aircraft waiting in a very long takeoff queue: "I'm ef...ing bored!"
    Ground Traffic Control: "Last aircraft transmitting, identify yourself immediately!"
    Unknown aircraft: "I said I was ef...ing bored, not ef...ing stupid!"

    Quote:
    Controller: "USA353 contact Cleveland Center 135.60." (pause)
    Controller: "USA353 contact Cleveland Center 135.60!" (pause)
    Controller: "USA353 you're just like my wife you never listen!"
    Pilot: "Center, this is USA553, maybe if you called her by the right name you'd get a better response!"

    Quote:
    "Pilot: "Tower, please call me a fuel truck."
    Tower: "Roger. You are a fuel truck."

    Quote:
    The German air controllers at Frankfurt Airport are renowned as a short-tempered lot. They not only expect one to know one's gate parking location, but how to get there without any assistance from them. So it was with some amusement that we (a Pan Am 747) listened to the following exchange between Frankfurt ground control and a British Airways 747, call sign "Speedbird 206":
    Speedbird 206: "Frankfurt, Speedbird 206 clear of active runway."
    Ground: "Speedbird 206. Taxi to gate Alpha One-Seven."
    The BA 747 pulled onto the main taxiway and slowed to a stop.
    Ground: "Speedbird, do you not know where you are going?"
    Speedbird 206: "Stand by, Ground, I'm looking up our gate location now."
    Ground (with arrogant impatience): "Speedbird 206, haff you not been to Frankfurt before?"
    Speedbird 206 (coolly): "Yes, twice in 1944, but I didn't stop."

    Quote:
    A Pan Am 727 flight engineer waiting for start clearance in Munich overheard the following:
    Lufthansa (in German): "Ground, what is our start clearance time?"
    Ground (in English): "If you want an answer you must speak English."
    Lufthansa (in English): "I am a German, flying a German aeroplane, in Germany. Why must I speak English?"
    Unknown voice (in a beautiful British accent): "Because you lost the bloody war!"

    Quote:
    Lost student pilot: "Unknown airport with Cessna 150 circling overhead, identify yourself."

    Quote:
    Tower: Cessna 172 say your altitude?
    Cessna (Student Pilot): We're at flight level 3500.
    Tower: Roger Cessna, contact NASA space center for further instruction.
    (Flight levels start at 18,000 feet and upwards. FL310 is shorthand for 31,000 feet. The student pilot has just informed ATC that he is flying at FL3500 or 350,000 feet)

    Quote:
    SR-71 Blackbird pilot Brian Shul reported one exchange. His SR-71 was screaming across Southern California, 13 miles high and its crew were monitoring cockpit chatter as they entered Los Angeles airspace. Though they didn't really control the SR-71, LA monitored its movement across their scope. The SR-71 crew heard a Cessna ask for a readout of groundspeed.
    "90 knots" Center replied.
    Moments later, a Twin Beech required the same.
    "120 knots," Center answered.
    An F-18 smugly transmitted, "Ah, Center, Dusty 52 requests groundspeed readout."
    Center (after a slight pause): "525 knots on the ground, Dusty".
    The SR-71 realised how ripe a situation this was for one-upmanship: "Center, Aspen 20, you got a groundspeed readout for us?"
    Center (after a longer than normal pause): "Aspen, I show 1,742 knots"
    No further groundspeed inquiries were heard on that frequency.

    In similar vein (airport not stated), an SR-71 crew were listening in on a similar "match this" contest. A Cessna asked to clear to 4000 ft, a corporate jet requested clearance to 12,000, an airliner to 18,000, etc. Finally the SR-71 called ATC.
    SR-71: "Request clearance to 80,000 ft"
    Tower: "Just how in hell do you plan to get up there?"
    SR-71: "Uh Tower, I'm descending to 80,000".
     
  12. Papabravo

    Expert

    Feb 24, 2006
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    That was a hoot -- keep 'em comming.
     
  13. beenthere

    Retired Moderator

    Apr 20, 2004
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    There is always the B-52 exchange:

    "Pilot to flight engineer, shut down four".

    Flight engineer to pilot, yessir, which four?".
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    Ok, this is the last bunch - it's great fun, but getting way off topic.

    A military pilot called for a priority landing because his single-engine jet fighter was running "a bit peaked."
    Air Traffic Control told the fighter pilot that he was number two, behind a B-52 that had one engine shut down.
    "Ah," the fighter pilot remarked, "The dreaded seven-engine approach."

    A huge C-5 cargo plane was sitting near where a small plane was waiting to take off. The private pilot got a little nervous because the military plane was closer than normal, and asked the tower to find out the intentions of the C-5. Before the tower could reply, a voice came over the radio as the C-5's nose cargo doors opened, saying, "I'm going to eat you." (Ack E Scharzmann)

    One day the pilot of a Cherokee 180 was told by the tower to hold short of the active runway while a DC-8 landed. The DC-8 landed, rolled out, turned around, and taxied back past the Cherokee. Some quick-witted comedian in the DC-8 crew got on the radio and said, "What a cute little plane. Did you make it all by yourself?" The Cherokee pilot, not about to let the insult go by, came back with a real zinger: "I made it out of DC-8 parts. Another landing like yours and I'll have enough for another one."

    From Dr Hugh David, June 2007 - Some years ago I was checking the record of simulated air-ground communication in a Real-Time simulation at the Eurocontrol Experimental Centre. Towards the end of one simulation I came across the following:

    French Simulator 'Pilot': "AF302 over NTM now."
    German Controller "AF302 Roger. Report names of stewardesses."
    FSP: "Claudette Colbert and Caroline Chose."
    GC: "Colbert I know, but who is Chose?"
    FSP: "You must know her, she was Alan Delon's third wife, between Truc and Nimporte!"
    GC: "Ach, these French actors, they marry and unmarry, I cannot keep track!"
    FSP: "Well, at least, the French actors, they marry VIMMEN!"
    ... (long pause) ...
    GC: "AF302 continue descent as planned."

    Light aircraft pilot asked Heathrow for the current cloudbase over Bristol. London relayed the question to an Air France flight near Bristol and got the reply:

    "Ve are at fifteen thousand, in and out the bottom."
    Anonymous voice on frequency: "Vive le sport!"

    Lufhansa Pilot to co-pilot, forgetting that the frequency was open: "We used to come up the Thames, and turn over here for the docks...."
    Voice on frequency: "ACHTUNG SPITFEUR"

    Novice female military controller to US bomber leaving radar coverage, forgetting the correct terminology... "You are entering my dark area"
    USB: "WHOOPEE!"

    Tower Controller: "BA356, proceed to stand 69"
    BA: "Yes, Sir, Nose in or Nose out?"

    QANTAS pilot to copilot landing at Sydney, forgetting the cabin intercom was live:
    "What I need now is a cold beer and a hot shiela"
    Stewardess hurries forward lest worse befall.
    Chorus of passengers "Hey, you forgot the beer!"

    A near miss occurred outside of Dulles International. The conversation went along these lines...

    Pilot: "D@#N! That was close..."
    IAD Tower: "Delta 560, what seems to be the problem?"
    Pilot (catching his breath), "Near miss- was he ever close!"
    IAD Tower: "Delta 560, how close was it?"
    Pilot: "Well, I can tell you one thing, it was a white boy flying it."

    From Mitch Reilly, May 2007 - I was listening to the radio, doing a preflight at MSP and heard the following exchange... My co-pilot did not hear it and gave me a strange look when I was doubled-over laughing. 'Northwest 605' was a DC-9. 'Flagship (Pinnacle) 5600' was a CRJ. The exchange went like this...

    Northwest 605: "Northwest 605 request taxi to the active MSP."
    Ground: "Northwest 605 taxi to runway **, follow the CRJ, you will be number two."
    Northwest 605: "Roger, we will follow the Smurf-Jet."
    Flagship 5600: "At least my airplane does not qualify for an AARP membership.."

    Tower: "Delta 351, you have traffic at 10 o'clock, 6 miles!"
    Delta 351: "Give us another hint! We have digital watches!"

    "TWA 2341, for noise abatement turn right 45 Degrees."
    "Centre, we are at 35,000 feet. How much noise can we make up here?"
    "Sir, have you ever heard the noise a 747 makes when it hits a 727?"

    Tower: "Delta 351, you have traffic at 10 o'clock, 6 miles!"
    Delta 351: "Give us another hint! We have digital watches!"

    "TWA 2341, for noise abatement turn right 45 Degrees."
    "Centre, we are at 35,000 feet. How much noise can we make up here?"
    "Sir, have you ever heard the noise a 747 makes when it hits a 727?"

    Control tower to a 747: "United 329 heavy, your traffic is a Fokker, one o'clock, three miles, Eastbound."
    United 239: "Approach, I've always wanted to say this... I've got the little Fokker in sight."

    A DC-10 had come in a little hot and thus had an exceedingly long roll out after touching down. San Jose Tower noted: "American 751, make a hard right turn at the end of the runway, if you are able. If you are not able, take the Guadalupe exit off Highway 101, make a right at the lights and return to the airport."

    A story from the late 1950's Navy flight training at Corpus Christi, Texas. Instructors were known to party hard at night, even before a 'hop' the next morning. A common 'cure' was to put on the mask and breathe the pure oxygen while the trainee got the craft airborne. The SNJ training aircraft had a tandum cockpit with intercom for personal communication between the instructor and the trainee. These 'private' communications would be broadcast on air if the intercom switch were accidentally left open. One such morning following a heavy night for one particular instructor, not long after the flight was aloft, the following was heard over the air: "Boy, am I ever f...ed up this morning." After a lengthy pause a young lady air traffic controller demanded: "Aircraft making that last transmission, please identify yourself." There was an even lengthier pause, and then a voice said: "Lady, I'm not that f...ed up." (Ack Mike)
    (The anecdote about breathing oxygen "the morning after" is true. Aircrew would sometimes come to Flight Equipment to "test" their masks)

    Tower: "Eastern 702, cleared for takeoff, contact Departure on frequency 124.7"
    Eastern 702: "Tower, Eastern 702 switching to Departure. By the way, after we lifted off we saw some kind of dead animal on the far end of the runway."
    Tower: "Continental 635, cleared for takeoff behind Eastern 702, contact Departure on frequency 124.7. Did you copy that report from Eastern 702?"
    Continental 635: "Continental 635, cleared for takeoff, roger; and yes, we copied Eastern... we've already notified our caterers."

    Allegedly, while taxiing at London's Gatwick Airport, the crew of a US Air flight departing for Ft. Lauderdale made a wrong turn and came nose to nose with a United 727. An irate female ground controller lashed out at the US Air crew, screaming: "US Air 2771, where the hell are you going?! I told you to turn right onto Charlie taxiway! You turned right on Delta! Stop right there. I know it's difficult for you to tell the difference between C and D, but get it right!" Continuing her rage to the embarrassed crew, she was now shouting hysterically: "God! Now you've screwed everything up! It'll take forever to sort this out! You stay right there and don't move till I tell you to! You can expect progressive taxi instructions in about half an hour and I want you to go exactly where I tell you, when I tell you, and how I tell you! You got that, US Air 2771?" US Air 2771: "Yes, ma'am," the humbled crew responded. Naturally, the ground control communications frequency fell terribly silent after the verbal bashing of US Air 2771. Nobody wanted to chance engaging the irate ground controller in her current state of mind. Tension in every cockpit out around Gatwick was definitely running high.
    Just then an unknown pilot broke the silence and keyed his microphone, asking: "Wasn't I married to you once?"
     
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