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Thread: Emergency Signaling, Emergency Beacons and Breitling’s EMERGENCY Wristwatch.

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    Picture Emergency Signaling, Emergency Beacons and Breitling’s EMERGENCY Wristwatch.




    Some Observations About Emergency Signaling, Emergency Beacons and
    Breitling’s EMERGENCY Wristwatch


    by Time Flies and altro (G. Buhyoff and A. Trott)

    G. Buhyoff is the technical author of this article which is written in the singular person based upon his experience with the subjects contained herein. He is a licensed pilot in the United States. A. Trott served as the text and technical editor and was also responsible for the detailed illustration of the article and its conversion into HTML and vB code formats. He is a glider pilot in the United Kingdom. The article is the result of an intensive collaboration between the co-authors.

    The Breitling EMERGENCY is unique in the world of horology; it is the first pilot's watch to be equipped with a 121.5 MHz locator homing beacon for communicating with search and rescue (SAR) services. Although another watch, the McMurdo Guardian is now available and also has an integrated 121.5 MHz locator beacon, it is meant for seamen; it activates upon contact with salt water and its beacon is not as powerful as the Breitling.

    The EMERGENCY is specifically designed as an important further item of safety equipment for pilots who already use 121.5 MHz for emergency radio (voice) transmissions and for their on-board Emergency Locator Transmitters (ELTs) that are triggered by excessive G-force during a forced landing or crash. Breitling has also supplied a number of EMERGENCY watches to some military pilots that transmit on 243.0 MHz. The company has long been known for designing watches with functions useful to aviators and the EMERGENCY is no exception.

    A lot could be said about the use and efficiencies of other emergency beacons, as well as radio and antenna design theory and survival techniques in general but much of that is beyond the scope of this article. The ultimate objective here is to help the owner get the best performance from his EMERGENCY should the need arise to activate its locator beacon. At the same time, it is useful to give the reader some background on the evolution of emergency signaling, and some basic understanding of the underlying variables that can influence the efficiency of the beacon transmitter contained in this watch. I shall discuss some crucial methods, based upon my antenna and transmitter design experience, for using its transmitter which are not covered in the owner's manual. There are simple techniques that can increase its efficiency and range during an aviation emergency and therefore increase the likelihood of a successful rescue.
    Note: A glossary of technical terms at the end of this article can be referred to if required.


    The Breitling EMERGENCY comes with a comprehensive manual and test equipment


    Non-radio Beacon Signaling Means and Devices

    The first emergency signals used by the military and civilians alike were primarily methods of attracting the attention of other pilots in the air or people on the ground. Most well-known are “signals in threes” – three columns of smoke, three blasts of a horn, or three blasts of a signal whistle. By the way, a whistle is an excellent signaling device and special whistles are made for survival situations and still issued to military pilots (eg the Fox 40 and the Jet Scream).

    The signal flare gun is another method that has been used for a long time and is still in use by the military and seafarers. Being a pyrotechnic device its use is limited by the flare burn time for catching the attention of a potential rescuer. They are more useful at sea or in open areas where they can be quickly and easily spotted but are less effective in areas with rough topography.

    Currently, many pyrotechnic flare guns are being replaced by laser flares – devices that in principle are not unlike those used for visual presentations but emitting a beam in the shape of a line rather than a point. They send the beam through a special optic that creates an expanding plane of light instead of a potentially harmful focused dot like a laser pointer making it easier to hit the intended target. Pointed at a nearby wall it produces a line a foot or so long. Pointed and slowly swept back and forth at a rescuer ten miles away, this same line will have expanded to 3,600 ft long. The line cannot miss anything in its path – any portion of the line viewed by rescuers appears as a brilliant red flash like a large red strobe light. As the rescuers get closer the length of the red laser line decreases and thus rescuers can "home in" on its location. Laser flares are popular with Alaskan bush pilots and are currently being adopted by the military. I carry a one in the survival vest I wear when flying over unforgiving terrain or water.



    The laser flare can replace a pyrotechnic flare and is much smaller and lighter than a flare gun


    A signal mirror is one of the cheapest and most effective emergency signaling devices a person can carry and with training can even be used in overcast conditions and at night.



    The signal mirror - simple and effective even in poor light conditions


    When used properly a signal mirror can be seen by SAR aircraft at up to approximately 50 miles under the right conditions. Any pilot will tell you that one thing that catches the eye very easily is a bright flash from a metal rooftop, another plane or even a small skylight on the roof of a house. I can personally attest to the effectiveness of signal mirrors from both my military and civilian flying experience.



    In full sunlight the signal mirror has a range of up to 50 miles


    Another non-radio beacon, the flashing strobe light, can be very effective although its ability to attract attention is best under dark conditions. Strobe lights are not seen very well in daylight or even at night if there is a summer atmospheric inversion haze layer. But strobe lights like the ACR Firefly 2 (still issued to military pilots and can be purchased by civilians) are excellent emergency signaling devices, small and easy to carry.



    Flashing strobe light - the Firefly 2


    Cellular and Satellite Phones

    Common electronic devices such as cellular and satellite phones can be extremely good emergency notification devices. Most of us have been amazed at times when we have managed to pick up a cellular phone signal in an outlying area, although equally, we have been frustrated when we could not.

    One pilot who had a "controlled flight into terrain" (a crash while trying to fly a crippled plane to a safe landing spot) in the mountains of Colorado was amazed that his cell phone worked despite being deep into the Front Range of the Rocky Mountains; he simply called 9-1-1 (universal emergency phone number in the U.S.). And, it was a good thing his phone did work since his on-board ELT had failed as a result of damage sustained in the crash and he did not have any other signaling device. Some of the newer cellular phones have Global Positioning Technology (GPS) built into them and this technology can be used to locate the phone. In the United States, the Federal Communications Commission (FCC) has mandated that all cellular service providers be able to trace a 911 emergency call to within 100 meters of its actual location by the end of 2005.

    However, being close to a cell phone network is obviously not something that can be relied upon, and therefore cell phones are only carried in addition to other safety and emergency equipment. Unfortunately, the areas where survival conditions are worst are generally areas where there is no cellular phone service.

    Satellite phones, despite the high cost for both handset and air-time, can be one of the better devices for emergency notification since they do not rely on cellular network access but rather link directly to satellites. Many bush pilots carry these phones but there are limitations to them. One problem is that although you can inform someone you need help, you also need to be able to locate yourself, preferably exactly. Technology does exist to track non-GPS satellite phones but location determination can be a lengthy process involving satellite signal triangulation and requiring the cooperation of the service provider. Fortunately new generation satellite phones have GPS capability and maintain latitude and longitude information within their memories.


    Radios and Electronic Beacons

    Emergency radio beacons, sometimes in combination with other signal devices and strategies, are the mainstay of modern emergency signaling. Most radio devices, including the Breitling EMERGENCY, send signals that perform both required primary functions; they notify that there is an emergency, and they provide a homing signal so that SAR can find the downed aviator even if he is unable to say where he is.

    Almost all survival radios and beacons work on one of three frequencies – the civilian 121.5 MHz in the VHF (Very High Frequency) band; the military 243.0 MHz also in the VHF band; or the more advanced digital combined civilian/military 406 MHz in the UHF (Ultra High Frequency) band. Currently 121.5 MHz (and often 243.0 MHz as well) is constantly monitored by commercial and some private aircraft. In addition, SAR satellites monitor for 121.5, 243.0 and 406 MHz emergency beacon signals. These polar orbiting satellites - SARSAT (Search And Rescue Satellite Aided Tracking, launched by the United States with Canada and France) and COSPAS (launched by Russia) - circle the earth every 102 minutes and view a constantly moving area of over 4,000 kilometers in diameter. They can "see'" or receive signals from between latitude 70 degrees North and 70 degrees South about every 45 minutes due to the size of their reception footprint.

    When the satellites receive an emergency signal on the analog 121.5 or 243.0 MHz frequencies they attempt to pinpoint its origin on earth. The signal is relayed to a ground receiving station which calculates the location of the origin of the signal by measuring Doppler shift caused by the relative motion between the satellites and the emergency beacon. This takes at least two orbits of the Cospas-Sarsat satellites but can take longer and up to several hours.

    Once a location is determined this information is sent to the SAR command post in the appropriate part of the world. In the U.S., Langley Air Force Base (AFB) in Virginia acts as the central SAR command post for North America. They then forward the information to the nearest SAR group or facility to mount the search.

    There are potential problems with this method of using 121.5 and 243.0 MHz and the orbiting Cospas-Sarsat satellites. Signals on the 121.5 and 243.0 MHz frequencies are subject to scattering and absorption by vegetation and do not penetrate structures very well since they are VHF. They are analog signals and not digital and are difficult to verify and since Doppler shift must be used, it can take a good while for the satellites to get enough consistent beacon signal information for the computations that are needed to accurately locate the beacon on the earth's surface. And, if the signal strength is low the problem is compounded. A weak signal can be due to the beacon having a low power transmitter (low specified power output or a low battery causing low output) or an antenna that is inadequate or not being used properly.

    Military beacon and voice-capable survival radios on 243.0 MHz preceded the civilian units now available that use 121.5 MHz. A 243.0 MHz homing sweep beacon could be transmitted for aircraft signal acquisition and monitoring, or the downed pilot could switch to voice communication with SAR personnel. They were rather large and heavy when first introduced but have saved many lives. The PRC-90 that I was issued during the early 1970s is a type used by the military until just a few years ago. They were very rugged units with an output of about 2 watts of power for eight hours from a single battery. We carried extra batteries and some pilots, including me, carried more than one radio since we subscribed to the philosophy of “if you have only one of something, it will not work when you need it”.



    Military beacon/radio - the PRC-90 from the 1970s


    At the time they were introduced, the signals from military survival radios were only acquired by search aircraft but not by satellite. Now, the Cospas-Sarsat as well as other special military satellites also can also acquire their emergency beacon signals.

    Since the advent of 121.5 Mhz for civil aviation emergencies, most general aviation (GA) aircraft are required under aviation regulations to have a 121.5 MHz ELT and in the United States in many cases, 243.0 MHz capability as well. The ELT must be located in the aft-most "accessible" portion of the aircraft (if of a non-portable type). This is the location that is most likely to experience the least amount of damage in the event of a crash or forced landing. These beacons are triggered by an inertia switch (often called a G-force switch) and begin to emit a distinctive downward swept audio tone on both frequencies. Military aircraft use a similar unit on the 243.0 MHz frequency and commercial air carriers use a 121.5/243.0 MHz and/or 406 MHz ELT.

    Click here to hear an ELT downward swept audio tone

    (If required, use your browser Back button to return to this article)

    Most civilian pilots also carry a backup hand-held aircraft band radio that is capable of transmitting voice on the 121.5 MHz frequency but these radios do not transmit an emergency beacon signal capable of being picked up by the Cospas-Sarsat satellites.


    The Good and the Bad Sides of Radio Frequency Harmonics and Spurious Emissions

    There has been and continues to be a major problem of false alarms on the 121.5 MHz frequency. It has been calculated that only 1 of every 1,000 emergency signals acquired by the Cospas-Sarsat satellites has been a valid emergency signal. This can be due to malfunctioning ELTs aboard civil aircraft; spurious emissions from electronic devices (appliances, stereo equipment etc); or radio frequency harmonics. Radio Frequency (RF) energy is a by-product of almost any device that utilizes electrical energy even if not designed as a radio transmitter. Sometimes these spurious emissions happen to occur at or about 121.5 or 243.0 MHz when Cospas-Sarsat can interpret them as valid emergency radio beacon signals.

    Radio frequency harmonics are generated by most all transmitting devices and other electrical devices as a “natural electronic process” of their functioning. For example, a device that was designed and intended for transmitting a radio frequency signal on or about 60 MHz will generate a first order harmonic at or near 121.5 MHz since 60 multiplied by 2 equals 120. Many neon sign ballasts have been to blame for generating false emergency signals on 121.5 MHz due to this harmonic generation problem, as well as stadium scoreboards, and even ATM machines! SAR missions have been deployed only to trace the signal to a “false hit” from electronic or electrical equipment. There are ways to control these harmonics but they involve expensive designs with very tight amplifier circuits and a series of filters to restrict the emission of “false frequency” harmonics.

    But, one last, important point must be illustrated here. The military emergency frequency of 243.0 MHz is the first harmonic of 121.5 MHz (121.5 x 2 = 243.0). This is advantageous and the “good part” of harmonics since a military or civilian aircraft that is monitoring the 243.0 MHz military emergency frequency will often pick up a 121.5 MHz emergency locator beacon transmission.

    The "false alert" situation on both 121.5 MHz and 243.0 MHz is a very real problem and has led to an important impending change in the use of this frequency.


    The Latest Developments in Emergency Locator Beacons

    Digital emergency radio beacons on 406 MHz, both PLBs and ELTs for aircraft, are the current technology. The PLBs are fairly small and lightweight, easily portable, and can be used for hiking, flying or any activity where there is some risk to personal safety.



    ACR 406 MHz Personal Locator Beacon


    Most commercial air carriers now use on-board 406 MHz beacons instead of ELTs that transmit on only 121.5 and 243.0 MHz and for many good reasons. These beacons transmit on the higher UHF frequency with greater power and are more effective in having quick and successful acquisition by the Cospas-Sarsat satellites as well as the Geostationary Operational Environmental Satellites (GOES). These additional GOES satellites positioned 22,300 miles above the equator cover very large portions of the earth on a continuous basis. (Many will be familiar with GOES satellite images from watching television weather broadcasts showing meteorological conditions such as hurricanes or large storms).

    An advantage of the 406 MHz frequency is that signals are less subject to absorption by surrounding objects such as metal and wood, or vegetation such as forest canopies. And, 406 MHz beacons use much higher output power (in the order of 50 times higher) than typical 121.5 and 243.0 MHz emergency beacons.

    Another advantage of the 406 MHz PLB or ELT is that they transmit a digital signal rather than the analog signal from 121.5 MHz and 243.0 beacons. The 406 MHz beacons send encoded digital information to the Cospas-Sarsat and GOES satellites that includes a special encoded identifier unique to a single PLB and that PLB is registered to a particular owner who has filed a form with personal information, including aircraft ID, names of contacts and phone numbers.

    When a 406 MHz beacon (PLB or ELT) is triggered, it takes the satellites less time to acquire the strong digital signal, Doppler shift computations take less time, and therefore the ground receiving station (such as Langley AFB) is notified sooner. The digitally encoded personal information can then be rapidly confirmed via phone calls to persons on the registered contact list provided by the owner.

    False alarms are virtually non-existent due to the fact that the 406 MHz beacons are digital and not analog. Harmonics problems are also virtually non-existent since an analog harmonic of 406 MHz that is accidentally generated by some device is easily filtered out as a false signal. Thus, search and rescue costs are greatly reduced since “false hits” are reduced to the point of virtual elimination.

    Civil aviation in the U.S. is being urged to convert their 121.5 MHz ELTs to 406 MHz ELTs. However, this is not likely to happen soon for private owners because of intense lobbying against it due to the costs of conversion.

    A big advance in digital PLBs is that you can purchase them with an additional integrated GPS. These GPS-integrated PLBs will not only send a beacon signal and the personal ID code but the beacon’s exact latitude and longitude as well and are made by companies such as McMurdo who are based in the UK as well as ACR (their non-GPS version is shown above). I have a McMurdo PLB with integrated GPS capability as well as the non-GPS ACR and my old military PRC-90 analog beacon/radio. These new PLBs are much lighter than the old military emergency beacon-radios due to their use of polymer-resin cases and are quite waterproof.



    McMurdo 406 MHz PLB with integrated GPS


    Doppler shift computations are not necessary with GPS-integrated units since the information they send includes their precise latitude and longitude. The time needed for the Cospas-Sarsat or GOES satellites to acquire a GPS-encoded signal, determine the location, and notify a ground receiving station can be under two minutes! In fact, during the last two years, the average time from a GPS-integrated 406 MHz beacon being triggered to the time of the SAR rescue unit deployment is less than one hour. This compares to an average time of 6 hours for 121.5 or 243.0 MHz emergency beacons which do not have integrated GPS. In addition, location pinpointing is much more accurate for GPS-integrated beacons.

    • Beacon transmitter type:............Time from acquisition to notification:.... Location resolution:
      121.5/243.0 MHz ..........................6 hours average, can be up to 24 hours........452 square nautical miles
      406 MHz ELT or PLB without GPS ....1 hour.............................................. .........12.5 square nautical miles approx
      406 MHz ELT or PLB with GPS..........5 minutes approx.......................................0.008 square nautical miles


    were originally intended to be homing signals NOT initial alert signals for satellites. The intention was that once someone was recognized as being in distress by some other means (radio voice message, eyewitness report, overflying aircraft etc) SAR would monitor the 121.5 MHz homing signal with direction finding antennas/receivers to locate the person exactly.


    The Future for 121.5 and 243.0 MHz

    While the prior discussion may seem unnecessary when speaking about a wristwatch ELT, it is important to understand the differences, limitations, constraints and capabilities of the ELT built into the Breitling EMERGENCY relative to what it does, how it can perform and how it compares to other types of emergency beacons. It is also important to realize how the way the watch can be used will change in the future.

    As of February 1, 2009, Cospas-Sarsat satellites will have their 121.5 MHz receivers turned off and will only receive 406 MHz signals. They will then no longer be able to be part of Doppler shift location computations. GOES satellites already do not monitor for 121.5 or 243.0 MHz emergency signals.

    However, SAR will continue to use 121.5 MHz as a homing signal and commercial and private aircraft will continue to monitor what is called the “Guard Frequency” of 121.5 MHz. As a side note, after the tragedy in New York City of September 11, 2001, all civilian private pilots in the United States are required to monitor 121.5 MHz when they are flying. This is so they can be communicated with by military fighter aircraft should they be intercepted while straying into a restricted flight area. Obviously the incentive for pilots to follow this requirement is strong!

    The Breitling EMERGENCY will still perform very useful local notification and homing functions from 2009 but its signal will no longer be acquired by satellites - unless that is, Breitling develop a 406 MHz digital model!


    The Breitling EMERGENCY Wristwatch



    A watch that continues to save lives


    To create the EMERGENCY, Breitling essentially took the Aerospace model and sandwiched it in a new titanium case with a miniaturized 121.5 MHz ELT beacon designed and built by Dassault A.T., the French aerospace company.

    The signal from an EMERGENCY is immediately identifiable as it contains the letter B in Morse code. This makes the transmission stand out from the 'clutter' of false alarms and non-aviation related (e.g. marine emergency beacons) signals on 121.5 MHz. A transmission from a Breitling EMERGENCY watch means one thing and one thing only: aviation emergency! It is not a false alarm or an overturned rowing boat or a lost hiker; it is a downed aircraft and immediate assistance is required.

    In the U.S., the Federal Communications Commission (FCC) initially decreed that only licensed pilots could own an EMERGENCY. Lobbying by the Aircraft Owners and Pilots Association (AOPA) and the Federal Aviation Administration (FAA) pointed out there could be situations where aircraft passengers needed to raise the alarm, and so later the FCC relaxed their ruling slightly bringing it into line with the rest of the world. Anyone may buy an EMERGENCY but it will be registered to a specific name and address; it may only be serviced by a Breitling Service Center; and most importantly of all, it may ONLY be deployed in a genuine aviation emergency.




    The watch's transmitter may only be used for its designated purpose


    As a matter of interest, after an EMERGENCY has been deployed it must go to back to Breitling for servicing; it cannot be used a second time. This puts further pressure on owners to use it only in a genuine emergency. And the service following deployment is free of charge having effectively been paid for when the watch was originally purchased. This policy ensures that owners will be very unlikely to let anyone else attempt to service the watch and so Breitling can continue to keep a tight control over its efficacy and reliability.

    The EMERGENCY watch is a wonderful concept in that it puts an ELT right on the wrist of the person who may need it. However, there are drawbacks since it has a low-power VHF transmitter (30 milliwatts - 0.3 of a watt). Its signal on 121.5 MHz can be absorbed by surrounding materials such as wood or metal and it is likely to be virtually ineffective if activated inside an aircraft hull. It is easily refracted by topography, structures or forest canopies and is absorbed and scattered by dense vegetation, rain, mist, or snow. The EMERGENCY has no GPS capability and the transmitter is analog, not digital. It is essentially a transmitter only for a homing signal for direction-finding capable aircraft and ground SAR personnel.

    But, do these limitations make it useless? No. It is still a highly capable 121.5 MHz beacon that will have a useful life well past 2009 since 121.5 MHz will continue to be used as an emergency locator homing signal frequency. All 406 MHz beacons transmit two signals - a digital satellite acquisition signal and a lower power 121.5 MHz SAR homing beacon signal. Is it as good as a 406 MHz ELT or PLB? No, it is not since its signal is weaker and subject to scattering, absorption and refraction and its signal is much more difficult to pick up by satellites. But it is far from impossible that the Cospas-Sarsat satellites can pick up a beacon signal from the EMERGENCY as long as it is used properly. And, that is key - to use it properly. The manual that comes with the watch is very general in its discussion and even vague with regard to some aspects of its proper use. Knowing how to use this device properly requires some discussion of the elements that make up its internal beacon - primarily, the transmitter and the antenna.


    So You Need to Use Your EMERGENCY? – Some Guidelines for its Use

    Before I tell you what to do if you need to use your EMERGENCY watch beacon, it is important to understand some basic ideas about how antennas work and why they are designed the way they are. This is important since it may well be through these examples that you will better recall what you should do with your EMERGENCY should you need to activate it. In my teaching career, I found that students remembered information about how to do something if they were taught how and why a concept or technique worked. That is, what made something do what it does. This underlying knowledge apparently triggers memory of the details of "how to do something".



    The ANTENNA cap covers the retracted main antenna


    All of the beacons I have discussed in this article use vertical antennas or “radiators”. The signals from these antennas all behave in a similar way since the antennas design is the same and they propagate (send out) signals in a generally similar geometric pattern. Some antennas can propagate a signal in a rather low angle pattern; others in a high angle pattern; and yet others can propagate a signal in omnidirectional or unidirectional patterns.

    The vertical antennas on all of the beacons, ELTS and PLBs I have discussed, including the EMERGENCY wristwatch, propagate signals in a fairly low angle omnidirectional manner. That is they send a signal at a fairly low angle of radiation (about a 20 to 30 degree arc from the horizontal surface of the ground) in a 360 degree pattern.

    Why is this important to understand? Well, the lower the angle of radiation, the further the signal will travel in an outward fashion. The higher the angle of radiation, the less horizontal distance the signal will travel as more radio frequency energy is radiated upward rather than outward.

    The picture below shows the military PRC beacon/radio and the ACR PLB with their antennas extended. (Of course they would be actually used with the antennas pointed vertically upwards).



    Antenna extension and position are crucial


    All vertical antennas have to work off a “ground plane”. This can be "true earth ground” – the actual ground/soil – or a “virtual earth” or “radials” - a length of wire or some other metal object to serve as a "ground image". I will not go into detail of the theory behind this, but want to emphasize the importance of the idea of a “ground plane” and of “virtual earth ground”. The next picture below shows one of my ham radio vertical antennas that I use to communicate via radio (voice, digital and Morse code) with people around the world (literally) via HF (High Frequency – roughly 3 MHz to 50 MHz). Note the two equal sides of the antenna – one above and one below the large middle cylinder. The bottom portion, below the larger cylinder in the middle, is the ground image, and the top part is the portion that radiates the signal. This antenna is called a vertical "dipole" since there are two poles (sections) that are on either side of a non-conductive center part (the larger diameter cylinder). The larger diameter middle cylinder contains something called a matching network and is not important to our discussion here. This is but just one variation of a vertical antenna. The important point is that a vertical antenna simply means an antenna that needs to be mounted in a vertical position.



    High frequency dipole antenna for long distance ham radio


    The EMERGENCY has its main antenna (the radiator) behind the cap marked “ANTENNA” at the bottom of the watch. The watch's transmitter is activated by unscrewing the antenna cap and pulling out the coiled antenna to its full length of 43 cm (17 ins). In use it should always be oriented as vertically as possible.



    The antenna is sufficiently rigid to stand vertically without support


    The "second antenna" as Breitling call it in their documentation (in both the manual and the VHS video tape that come with the watch) is really a “virtual ground” known as a “radial”. This radial and the metal of the watch itself provide the ground image for the "radiator", the main antenna that actually transmits the signal. In fact when you deploy both antennas on the EMERGENCY you have an antenna system that looks a lot like the dipole antenna used for ham radio. In these antenna systems there are two physical sections to the antenna – one connected to electrical ground and one connected to the positive output from the transmitter amplifier.



    The cap near 11 o'clock covers the retracted second or radial antenna


    Let’s take a look at another type of antenna – one that uses more than one “radial”. The example I will use here is called a discone antenna because it is an antenna in a cone shape. These antennas are used at airports for communication on the aircraft frequencies which range from about 118 MHz to 134 MHz. The image below is a discone antenna at my house that I use to communicate with my airplane when my son is flying it or with another pilot I may know and to whom I want to pass a message.



    Discone antenna used for contacting aircraft


    A discone antenna has one vertical "element" at the top that radiates the signal, and a set of elements (rods), often oriented at an angle of about 45 to 60 degrees, below. Those elements (rods) under the vertical element are “radials” that are usually a fractional multiple of the wavelength of the frequency being radiated by the vertical antenna. The length of these radials is often determined by a mathematical formula to compute the electrical resonant length of the frequency that the antenna is designed to transmit and receive. The closer the length of the radials to a fractional or whole multiple resonant length for a given frequency, the greater the efficiency of the antenna to perform on that frequency. The "second antenna" of the EMERGENCY is a fractional resonant length of wire for the frequency of 121.5 MHz.

    The more radials you use, the stronger will be the signal that is propagated and acquired at the receiving end (satellites, SAR direction finding receiver, etc). Not only will the use of radials or a metal ground plane increase the signal strength radiated by the antenna, but it also lowers the "take-off angle" of the radiated lobe of the signal. Hence, the signal will travel further along the horizontal plane - its effective radius will be longer. In other words, your signal will travel a greater distance (but at a lower angle) while your chance of being heard increases due to increased signal strength (assuming you are out in the open). But there is a trade-off. The more signal you send out along or near the horizontal, the less will leave the antenna traveling upwards at a steeper angle, and vice versa. There is a finite amount of RF energy that a transmitter sends to the antenna - no more and no less. So, if most of the signal is propagated along one plane then less is propagated along another plane or, what is called a propagation lobe (a geometric pattern of the signal as it radiates from the antenna).

    If in a forced landing or crash, first make sure your on-board ELT has triggered to 'on' and activate it manually if necessary. Do not rely on the G-force trigger having worked since they have a high documented rate of failure. Interestingly though, they sometimes trigger as the result of a hard landing. Next, check to see that your ELT antenna is still connected to the airframe since these are often torn off in a crash, especially if you were involved in a forced landing and hit trees or some other object.

    The on-board ELT puts out a stronger signal than the EMERGENCY since its output is about 3 times greater (commonly, on-board ELT output is around 100 milliwatts or 0.1 watt on average). On-board ELTs use much of the metal aircraft hull and airframe as a ground plane. Remember, the more metal under the antenna the greater the signal strength propagated by the antenna. There is no need to use up the batteries of two ELTs at the same time. Use the more powerful ELT first since you want, more than anything at this stage, to have your signal acquired by Cospas-Sarsat or the GOES satellites if the ELT is a 406 MHz version. Satellite acquisition is far more likely using the ELT with more power and with a larger ground plane (the aircraft hull). This assumes you are going to stay by your aircraft after assessing a lack of danger from explosion or fire from leaking fuel. Of course it is always best to stay by the aircraft if at all possible since it is the easiest thing for search and rescue to see from the air and your on-board ELT may continue sending out a signal that is stronger and more easily to DF (direction find) than portable equipment.

    I would not use my EMERGENCY watch until I had to do so. If my primary on-board ELT were not working after checking with my aircraft radios (assuming they still worked) or with my backup hand-held aviation radio (by tuning to 121.5 MHz and listening for the ELT beacon sweep) then I would activate my EMERGENCY watch beacon. I would first use it with the main antenna and I would NOT pull out the “second antenna” at this time since this second antenna is just a radial to provide additional ground image. Instead, I would try to set my watch on its edge on top of the aircraft or a large metal part of the airframe or fuselage after scraping away the paint and making sure I had metal to metal contact. The metal of the aircraft will provide a larger surface area and so a much better ground plane for the antenna than the “second antenna" (radial) coiled up in the watch. And, this will give a lower take-off angle for the propagated signal from the watch’s internal ELT beacon.

    Make sure to keep that antenna pointed as straight up as you can. If you are not able to create a large ground plane (by using the aircraft metal) then you should use the second antenna pulled out and aimed downwards with the main antenna aimed vertically up. Make sure the main antenna does not touch anything especially metal or even any part of your body or clothes if wet. If you need to wear the watch and continue transmitting (such as if leaving the area of the downed aircraft due to weather or other threats) then make sure you keep your arm at an orientation that keeps that main antenna pointed as vertical as possible. If you feel the antenna touching any part of your body then put something non-conductive between the antenna and your skin (a dry rag or something similar - make sure it is not wet as it would have become conductive). It does not matter as much if the “second antenna” (radial) from the smaller diameter tube at the top of the watch touches you as you will just contribute to the ground plane affect.

    Recall that I just said that more metal underneath the watch increases the ground plane effect and decreases the take-off angle of the radiated signal from the antenna. If I were to go down in a mountainous area, I would not want my antenna to have a low take-off angle, but rather one that was higher or in a sense “more straight up” in order to allow over-flying aircraft to detect the signal rather than have it absorbed, reflected or refracted by the surrounding high terrain. The propagated signal won’t actually be straight up but the angle of radiation will be much higher (about 50-70 degrees from the horizontal). In other words, I would use both the main and second antennas in the watch and either wear the watch or fasten it to a tree or the highest point you can manage. Do not leave the area near where you have fastened the watch. That watch is now your best bet of SAR personnel finding you rather than just your plane or your watch attached to a tree branch!

    Again, let the on-board aircraft ELT do its job as long as it is functioning. Activate your watch once you see that there are aircraft flying overhead or once you have a sense that search and rescue is in the area. The EMERGENCY will emit the standard 121.5 MHz homing signal and also in a set, timed sequence transmit a Morse code letter "B" (dash dot dot dot - sounds like dah di di dit) that designates the signal as coming from a Breitling EMGERGENCY watch ELT.

    The EMERGENCY is particularly useful if you need to leave the scene of the accident. One big advantage of the watch (and one reason why I bought one) is that although I can’t take my aircraft ELT with me, I can take my watch. And the purpose is for SAR personnel to find me not the plane, per se. Again, the EMERGENCY is marginal in its output power for satellite reception. If I were in mountainous terrain and capable of moving without danger to myself, then I would get into a position as high as possible since I would be in a more open position and my chances of having the EMERGENCY watch ELT signal picked up by satellites would be improved immensely. If I were not in hilly or mountainous terrain I would move to a clear area since this would minimize the very real problems of signal absorption, reflection and refraction.

    The ideal place to go down as far as the EMERGENCY’s beacon performance is concerned would be in or near salt water. Salt water is highly conductive and acts as a huge ground plane. Since there are no obstructions you would not need to pull out that “second antenna” and you would literally be located within a huge ground plane. Of course though, water ditching has a whole set of other bad things going for it. Remember, the watch is mainly meant as a means to help SAR find you once they know you are down - as a result of a missing aircraft report; satellite acquisition and notification of Langley AFB; Air Traffic Control or a Flight Service Station informing them of a flight plan that was not closed; or another aircraft picking up your on-board ELT signal.


    Some Comparisons of Emergency Locator Transmitters and the Bottom Line

    I think it is useful to compare the 121.5 MHz transmitters in the four emergency beacons I own and have talked about in this article – my aircraft on-board ELT; an ACR PLB (made in the U.S.); a McMurdo Fast Find Plus PLB (British); and my Breitling EMERGENCY. There are two main factors that contribute to transmitting an effective signal – the output power and antenna efficiency. So, what are the differences in power output between these four 121.5 MHz locator beacons?



    As it turns out, the differences are not really that great:

    • On-board, permanently mounted aircraft ELT: 90 mw for 48 hours
      Breitling EMERGENCY watch: 30 mw for 48 hours
      McMurdo PLB with GPS: 50 mw for 24 hours
      ACR PLB without GPS: 25 mw for 24 hours

    Good job, Dassault! Dassault Aviation have obviously done a lot of homework in designing this transmitter, especially with regard to power consumption from such small and low voltage and amperage batteries. To design such a small transmitter with such potentially good efficiency and low power drain is quite a feat.

    However, please recall that the 406 MHz PLBs are not using the low power output 121.5 MHz transmitter for the purpose of having satellites acquire this frequency. They use a high power (5 watt) transmitter at 406 MHz for satellite acquisition. Their internal 121.5 MHz transmitters are for homing and direction finding by SAR personnel only. But, if you compare 121.5 MHz transmitters for all of these devices, the EMERGENCY does quite well given its small size. In fact, it does very well. In real terms, it has the potential of being only about 2 units of signal strength (on a ten point scale) weaker at the receiving end than my on-board aircraft ELT and roughly about the same signal strength, at the receiving end, as the 121.5 MHz homing beacons in my PLBs.

    The bottom line is that the EMERGENCY is not equal to a 406 MHz beacon with regard to effectiveness but it should hold its own as a decent homing beacon to get you found once someone knows your approximate location. But if you rely on the EMERGENCY alone it is highly likely that it will take SAR longer to be notified due to the low output power and the increased difficulty Cospas-Sarsat satellites will have in acquiring a low power 121.5 or 243.0 MHz signal.

    For my needs and requirements, the EMERGENCY watch is not a primary signaling device. Its limited power and the fact that it is really more of a homing beacon limits its usefulness despite it having the theoretical capability of being only about 60% less efficient than the 121.5 MHz ELTs mounted on-board my aircraft. My view is I would rather use the EMERGENCY as "additional insurance". When I am flying I always carry a 406 MHz Personal Locator Beacon with integrated GPS in addition to my aircraft ELT. For bush flying I would carry a satellite phone and, if possible, a small, portable high frequency (HF) radio (radio license required to use such equipment). So my EMERGENCY is really a third or fourth order backup device. But, I would rather have that third or fourth option in any situation that causes me to use those emergency notification or communication devices.

    Enjoy your EMERGENCY, if you own one, and use it properly and knowledgably. I wish you all the best of luck and hope you never need to activate the beacon on this very unique timepiece. I hope I have added some additional insight about emergency signaling; the operation of emergency beacons in general; and some specific suggestions to get the most out of the 121.5 MHz beacon in the Breitling EMERGENCY.



    THE watch!


    Jargon Buster - techno-babble demystified:



    • Acquisition = Reception of radio signal.
      AFB = Air Force base.
      Antenna = Transmitter aerial; can come in various configurations (e.g. vertical, horizontal) - see also second antenna and ground plane.
    • AOPA = Aircraft Owners and Pilots Association - influential world-wide body for private owners and pilots.
      Band = Section of possible radio wavelengths e.g. HF, VHF, UHF, Microwave.
      Beacon = Device that issues continuous radio signal - marks the position of the sender.
      COSPAS = Russian earth-orbiting satellite that monitors distress signals; part of the Cospas-Sarsat system.
      Cospas-Sarsat = The combined U.S./French/Canadian and Russian system comprising COSPAS and SARSAT satellites.
      DF = Direction Finding; Direction Find.
      Dipole antenna = Antenna with two sides, one being a ground side and the other a radiator that emits a radio frequency (RF) signal.
      Discone antenna = A vertical antenna with radials in a cone shape like those used for communications with aircraft.
      Doppler = Effect on received radio signal when approaching/moving away from transmitter.
      Elements = The virtual ground plane and radiator portions of an antenna.
      ELT = Emergency Locator Transmitter - radio beacon device.
      FAA = Federal Aviation Administration - responsible in the U.S. for aviation matters.
      FCC = Federal Communications Commission - responsible in the U.S. for radio communications matters.
      Flare gun = Pyrotechnic flare launcher - for fireworks-type flares.
      GA = General Aviation - civilian non-airline aviation.
      GOES = Geostationary Operational Environmental Satellites - in fixed orbit above the earth; provide environmental downlink information; have 406 MHz emergency signal receiver in payload.
      GPS = Global Positioning System - intercepts satellite signals and gives precise latitude/longitude position.
      Ground plane = Second or complementary antenna - can be actual (true) ground (earth) or virtual (e.g. second antenna).
      Guard frequency = Radio Frequency 121.5 MHz internationally reserved for distress communications.
      Harmonic = Multiple of frequency - analogous to octaves in music.
      HF = High Frequency radio signal wave length (1.0 – 50 MHz) - lower in frequency than VHF.
      Homing signal = Radio beacon transmission for SAR to follow to downed aviator.
      Laser flare = Modern replacement for flare gun - sends a laser beam in a line rather than a focused "spot".
      Milliwatt = One milliwatt is one thousandth of one Watt (see also Watt).
      MHz = Mega Hertz - unit of radio wave frequency; higher frequency gives greater penetration of obstacles.
      Monitor = Receive and interpret radio signal.
      PLB = Personal Locator Beacon - portable transmitter of radio signal and can send digital GPS co-ordinates.
      Propagate = Transmit; broadcast; radio frequency waves as they are emitted from an antenna in a set pattern.
      Radials = Act as a virtual earth ground; the ground side of an antenna; are resonant lengths of the frequency being transmitted either in whole multiples or in lengths that are fractional multiples of the transmitted frequency – they act as a ground plane to increase antenna propagation efficiency.
      Radiator = Main antenna of transmitter; the antenna part that actually radiates the radio frequency signal.RF = Radio Frequency - a radio signal.
      SAR = Search And Rescue - those who save downed aviators.
      SARSAT = U.S. earth-orbiting satellite that monitors distress signals; part of the Cospas-Sarsat system.
      Satellite phone = Portable telephone that works from anywhere via satellite up and down link - does not need a network.
      Second antenna = Complementary antenna or ground plane known as a radial - can be antenna, metal object or other (see ground plane).
      Strobe = Extremely bright flashing light used to draw attention.
      UHF = Ultra-High Frequency radio signal wavelength - higher than VHF.
      VHF = Very High Frequency radio signal wavelength - higher than HF, lower than UHF.
      Watt = Unit of power of transmitter - see also milliwatt (mw) which is a fraction of one Watt.



    Copyright © 2005 G. Buhyoff/A. Trott. All rights reserved. Please contact us for permission for commercial or non-commercial use.
    Last edited by SnapIT; March 28th, 2011 at 10:08. Reason: to improve layout - no change to content.
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