Requested Signals

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Requested Signals[edit]

If you have these signals (or any other not on the list) please either add the waterfall image and sample sound as an MP3 to the wiki and edit the page, or contact us at sigidwiki__AT__gmail__DOT__com for addition. Please consult the instructions here - Adding An Example Signal.

 Signal description
Advanced Civil Speed Enforcement System (ACSES II)
  • System overlaid on track circuits and cab signal as required by FRA for High Speed 150 mph AMTRAK operation on NEC (Acela trains)
  • Originally conceived by AMTRAK (Larry Light)
  • Used exclusively on NEC for AMTRAK
  • Original version does not have TSR radio transmission – portable programmable transponders used instead – being superseded by ACSES II with TSR radio at 220 MHzMegaHertz (MHz) 10^6 Hz.


  • SUPPLIER(s): Alstom/PHW
  • STRUCTURE: ACSES II CDMACode Division Multiple Access/TDMATime Division Multiple Access standard
  • MAX BIT RATE: approx 9600 bpsBits per second (bps)
  • FREQ BAND: 900 MHzMegaHertz (MHz) 10^6 Hz ATCS Channels, being converted to 220 MHzMegaHertz (MHz) 10^6 Hz at 12.5 kHzKiloHertz (kHz) 10^3 Hz channel spacing.
  • COMMS RANGE: LOS with controlled power output
  • COMMS BETWEEN: Wayside base station and train
  • STATUS: In service - Northeast Corridor (2012)


  • SUPPLIER(s): Alstom/Ansaldo
  • STRUCTURE: Eurobalise - short distance
  • MESSAGING STD: Eurobalise, 170 bits data, 72 bits CRC, 255 total bits
  • FREQ BAND: 27 MHzMegaHertz (MHz) 10^6 Hz carrier energize, 4.5 MHzMegaHertz (MHz) 10^6 Hz response FSKFrequency-Shift Keying message
  • RADIO MFGR: Alstom Europe/ Ansaldo Europe
  • DISTANCE RANGE: about 10 feet
  • COMMS BETWEEN: track mounted xponder and locomotive or MU Car
  • STATUS: In service – Northeast Corridor
Advanced Pager Operating Code (APOC)Advanced Pager Operating Code. A new mode, developed by Philips Telecom and announced in 1993, that offers higher speed and some new features while retaining backwards compatibility with POCSAG. Supports bit rates between 1200 to 6400 or about 1200 to 3200 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. using 2-PAMPulse Amplitude Modulation/FMFrequency Modulation or 4-PAMPulse Amplitude Modulation/FMFrequency Modulation modulation. Extended addressing is supported, allowing support for more then 2 million pagers. As of mid-1996, Philips has dropped APOC and instead settled a cross-licensing deal with Motorola for access to FLEX.
Advanced Paging Operations Code (APOC)The Advanced Paging Operations Code (APOC) is a proprietary pager protocol of Philips Paging. The format has been designed to allow POCSAG paging systems to gracefully introduce new paging features and capabilities in an existing paging network. These enhancements include extra channel capacity, extended battery economy and additional network features. It has been designed to coexist with standard POCSAG transmissions. Under the APOC enhancements, mixed data transmission speeds may operate on a single channel. Standard APOC operates as a 1200 bit per second transmission, but, data codewords may be sent at 2400, 3200, 4800 or 6400 bits per second. This is accomplished by sending specialized POCSAG synchronization codewords at the 1200 bit per second rate, which indicate that in the period of a standard 1200 bit per second POCSAG batch, data will be transmitted at a specific data rate.
Advanced Railroad Electronics System (ARES)
  • First system to use GPS for train location
  • Derived from Boeing 757/767 avionics system.
  • Intended to protect freight and passenger trains from mishaps
  • Demonstrated on 250 miles in Minnesota. Cost, management, and crew issues stopped it.
  • SUPPLIER(s): Rockwell Collins Demo 1985-1993
  • STRUCTURE: Proprietary
  • MESSAGING STD: UNK - proprietary ?
  • MAX BIT RATE: 2400
  • FREQ BAND: MICROWAVE (Pt-to-Pt), VHFVery High Frequency (30-300 MHz) 160 MHzMegaHertz (MHz) 10^6 Hz
  • RADIO MFGR: AAR Standard Radios (GE, Motorola, Harris, etc.)
  • DISTANCE RANGE: Line of Sight (LOS)
  • COMMS BETWEEN: Base Wayside Locomotive
  • STATUS: ARES shut down in 1993 in Minnesota
Advanced Speed Enforcement System (ASES)
  • Overlay for New Jersey Transit
  • Merges two systems--continuous cab signaling and positive train stop (PTS) by intermittent cab linked to xponders.
  • The intermittent cab signal portion of the
  • Brings a train to a stop if it should run through a red signal, even if the train is traveling at less than 20 m.p.h.
  • Uses transponders to transmit speed enforcement data to train in each block.
  • Similar to ACSES except in-cab speed display was more sophisticated.
  • Had some technical issues when deployed – Ansaldo Sweden cab signal.

  • SPONSOR: NJ Transit
  • SUPPLIER(s): US&S - Ansaldo
  • MESSAGING STD: Eurobalise
  • FREQ BAND: 27 MHzMegaHertz (MHz) 10^6 Hz
  • RADIO MFGR: Ansaldo
  • COMMS RANGE: 6 feet
  • COMMS BETWEEN: Transponders and Train
  • STATUS:Not in use, to be superseded by ACES II (PTC system = ACSES II)
BART Advanced Automated Train Control (AATC)
  • Planned to replace long-troubled BART (Bay Area Rapid Transit, San Francisco) track circuit based designs in a “standalone” manner. Several “kludges” for train separation would be replaced.
  • Derived from military vehicle location and comms system by Hughes Aircraft later acquired by Raytheon.
  • RFRadio Frequency comms provided location by triangulation plus high speed data comms with trains.
  • Turned over to Harmon when Raytheon realized they couldn’t commercialize.
  • Many technical issues with translating from surface to subway application.
  • Development halted by GE after takeover of Harmon and subsequent customer issues.

  • SYSTEM: Advanced Automatic Train Control (BART)
  • SUPPLIER(s): Raytheon then Harmon then GE
  • STRUCTURE: ISO 7 layer
  • MAX BIT RATE: Very high - 128 KBPS
  • FREQ BAND: UHFUltra High Frequency (300-3000 MHz) – military 420 MHzMegaHertz (MHz) 10^6 Hz proposed
  • RADIO MFGR: Raytheon (for demonstrations)
  • COMMS RANGE: Short range multiple TXTransmit/RXReceive for location and data transmission
  • COMMS BETWEEN: Among multiple waysides and to trains at all times
  • STATUS: Contract cancelled / project abandoned by GE after Harmon acquisition.
BluetoothBluetooth is a wireless technology standard for exchanging data over short distances (using short-wavelength UHFUltra High Frequency (300-3000 MHz) radio waves in the ISM band from 2.4 to 2.485 GHzGigaHertz (GHz) 10^9 Hz) from fixed and mobile devices, and building personal area networks (PANs). Invented by telecom vendor Ericsson in 1994, it was originally conceived as a wireless alternative to RS-232 data cables. It can connect several devices, overcoming problems of synchronization.
C-NetzThe Radio Telephone Network C (German: Funktelefonnetz-C, abbreviated as C-Netz), was a first generation analog cellular phone system deployed and operated in Germany (at first West Germany) by DeTeMobil (formerly of Deutsche Bundespost Telekom, currently Deutsche Telekom). It utilized the C450 standard and was the third and last update of a series of analog mobile phone systems used primarily within Germany, superseding the B-Netz and the A-Netz before it. It has been decommissioned, replaced by both the newer D-Netz (GSM-900) and E-Netz (GSM-1800) systems.
CognitoCognito Mobile Data solutions (Cognito is now Cognito IQ), data communications at 9.6kbps. Found in Cognito radio modems. Found in the UK.
Communication Based Train Control (CBTC)
  • Utilized by New York City Transit (NYCT)
  • True Moving block CBTC with local zone control
  • Radio system is a (proprietary) high-speed vital local area network between train & zone controller and between zone controllers
  • Zone Controllers use fiber based physical network to other zone controllers
  • Both above ground and subway tunnel operation.
  • Uses Transponders for train location with tachometer type incremental navigation

  • SPONSOR: New York City Transit
  • SUPPLIER(s): Siemens + Thales
  • STRUCTURE: IP Messaging Scheme – proprietary application
  • MESSAGING STD:WLAN Siemens std.
  • MAX BIT RATE: 128 KBPS per train (4 MBPS total max)
  • FREQ BAND: 5.725Ghz - 5.825Ghz
  • RADIO MFGR: Siemens Type PULZ80
  • COMMS RANGE: limited
  • COMMS BETWEEN: Wayside zone controllers and Trains and other zone controllers
  • STATUS: Operating on NYCT Canarsie Line (2012), being installed on PATH, NYCT Flushing Line and Culver Line Test Track.
Communications Based Train Management (CBTM)
  • Non-vital overlay PTC system from Wabtec
  • First application specific to “dark” territory, signaled operation to come later
  • Only goal to advise crew of need to stop/slow and enforce if no action taken.
  • In-cab display activated only when warning or alert needed for crew use, else blank.
  • Was demonstrated over 50 mile coal line territory
  • Intended to integrate with “NGD - New Generation Dispatch” at CSX HQ.

  • SUPPLIER(s): Wabtec
  • RADIO MFGR: MeteorComm
  • COMMS BETWEEN: Wayside and Locomotive & Office and Locomotive
  • STATUS: Demonstration terminated - Superseded by I-ETMS and RSIA 08
Digital Multimedia Broadcasting (DMB)Digital Multimedia Broadcasting (DMB) is a digital radio transmission technology developed in South Korea as part of the national IT project for sending multimedia such as TV, radio and datacasting to mobile devices such as mobile phones, laptops and GPS navigation systems.
Digital Terrestrial Multimedia Broadcast (DTMB)DTMB (Digital Terrestrial Multimedia Broadcast) is the TV standard for mobile and fixed terminals used in the People's Republic of China, Hong Kong, and Macau. Previously known as DMB-T/H (Digital Multimedia Broadcast-Terrestrial/Handheld), the DTMB is a merger of the standards ADTB-T (developed by the Shanghai Jiao Tong University), DMB-T (developed by Tsinghua University) and TiMi (Terrestrial Interactive Multiservice Infrastructure); this last one is the standard proposed by the Academy of Broadcasting Science in 2002.
DropsondeA dropsonde is an expendable weather reconnaissance device created by the National Center for Atmospheric Research (NCAR), designed to be dropped from an aircraft at altitude to more accurately measure (and therefore track) tropical storm conditions as the device falls to the surface. The sonde contains a GPS receiver, along with pressure, temperature, and humidity (PTH) sensors to capture atmospheric profiles and thermodynamic data. It typically relays these data to a computer in the aircraft by radio transmission.
Electronic Train Management System (ETMS)
  • System development contracted by BNSF to Wabtec
  • Work started in late 1990s after PTS and ARES
  • Non-vital overlay with continuous in-cab display
  • Deployed in several territories with different operating methods.
  • BNSF continues to expand and refine ETMS, I-ETMS is a spin off.
  • Uses MeteorComm radio

  • SUPPLIER(s): Wabtec
  • MESSAGING STD: MeteorComm proprietary
  • FREQ BAND: 900 MHzMegaHertz (MHz) 10^6 Hz being converted to 220 MHzMegaHertz (MHz) 10^6 Hz
  • RADIO MFGR: MeteorComm
  • COMMS BETWEEN: Wayside and Locomotive & Office and Locomotive
  • STATUS: In service on several different territories (as of 2012), being expanded per RSIA 08
Emergency Managers Weather Information Network (EMWIN)The Emergency Managers Weather Information Network (EMWIN) is a system for distributing a live stream of weather information in the United States. The backbone of the system is operated via satellite by the U.S. National Weather Service (NWS), but data are transmitted over radio repeaters by the NWS, citizens, and other organizations in many regions, and information can also be downloaded via the Internet. Local VHFVery High Frequency (30-300 MHz)/UHFUltra High Frequency (300-3000 MHz) radio rebroadcasts and older-generation EMWIN satellite systems operate at the speeds of 1200 and 9600 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second.. EMWIN data consists of textual observational and forecast information, including a limited number of cloud and radar images. The new EMWIN, labeled EMWIN-N, began being upgraded in 2009. The upgrade continues through 2011 to ready older GOES satellites to provide a higher speed of 19.2 kbit/sKilobits per second (kbps).[1] The data broadcasts are monetarily free with both local rebroadcasts and satellite feeds. EMWIN weather data is primarily transmitted over GOES satellites that observe the United States. The new satellites are the GOES-N series, and are designated GOES 13, GOES 14 and GOES 15.
EurofixEUROFIX, A DELFT UNIVERSITY CONCEPT to integrate GPS and Loran-C. Eurofix time-modulates the Loran-C pulses, producing a reliable data link out to a range of about 1,000 km. The Eurofix modulation scheme uses the last six pulses of the standard LORAN pulse group (Figure 9). These pulses are Pulse Position Modulated (PPMPulse Position Modulation) by ±1 μs. There are 729 possible modulation patterns. To minimize the impacts to users, the PPMPulse Position Modulation encoding uses 128 of a possible 141 balanced patterns to represent seven bits of data per Group Repetition Interval (GRI). The data rate is 70 to 175 bits per second, based on the GRI, and uses forward error correction (Reed-Solomon encoding) [8]. The Eurofix message length is fixed at 210 bits with consisting of 30 seven-bit words (GRIs). Seventy bits are used to represent the application data, while the remaining 140 bits are used for the forward error correction. The 70 bits of application data are structured such that four bits indicate the message type, 52 bits contain the application data, and there are 14 Cyclic Redundancy Check (CRC) bits. There are 16 possible message types that can be broadcast using Eurofix with Message Type 6 providing the UTC data [9].
General Packet Radio Service (GPRS)
High Resolution Picture Transmission (HRPT)
InFLEXionAnother member in the family of FLEX™ protocols is InFLEXion™, Motorola's advanced voice and data messaging protocol utilizing both FMFrequency Modulation and Linear modulation signaling methods. The FCC action to release 50 kHzKiloHertz (kHz) 10^3 Hz wide Narrow Band PCS channels has allowed the InFLEXion™ technology to become available. The InFLEXion™ protocol allows for the creation of a voice and data messaging network with frequency reuse capabilities similar to that of cellular telephony. The protocol is based upon the ReFLEX™ protocol already discussed. It is also possible to operate completely in a simulcast mode. Other FLEX™ type protocols may be mixed on an InFLEXion™ based channel. InFLEXion™ based systems make specific use of the ReFLEX™ capability to request a messaging unit to respond to a location request, combined with directed transmission of pages within specific geographic areas. The messaging unit response enables the network control equipment to determine the specific geographic area in which the messaging unit is located. Using this response, a voice message may be sent to the nearest transmitter(s) to which the pager is currently located. The voice messaging over the 50 kHzKiloHertz (kHz) 10^3 Hz channels features variable compression techniques allowing equal to or greater than 24 times the subscriber capacity of today's 25 kHzKiloHertz (kHz) 10^3 Hz channels. Simultaneously, other voice messages may be delivered on the same frequency to messaging units which are geographically separated from each other so that there will be no transmission interference. With InFLEXion™ Data signaling the throughput on the 50 kHzKiloHertz (kHz) 10^3 Hz channel allows signaling of up to 112 Kbps As in ReFLEX™ systems, the InFLEXion™ protocol provides a choice of multiple inbound signaling speeds to allow the system structure to operate with the fewest number of receiver sites for a given traffic level.
Incremental Train Control System (ITCS)
  • Began with Conrail/MDOT/AMTRAK to speed up passenger trains across Mich.
  • Initial development in mid 1990’s – still being upgraded to original 110 mph target
  • Includes advanced crossing start for high speed trains.
  • Was Harmon system based on VHLC and UltraCab Cab Signal designs.
  • Uses distributed “zones” of control which communicate peer-to-peer with vital data

  • SUPPLIER(s): Harmon then GETS-GS
  • STRUCTURE: OSI 7-layer GE proprietary layers 2, 3, 5, 7 TCP/IP and TDMATime Division Multiple Access
  • MESSAGING STD: Proprietary application over IP
  • FREQ BAND: 220 MHzMegaHertz (MHz) 10^6 Hz
  • RADIO MFGR: GE MDS spread spectrum radio
  • COMMS RANGE: Dependent on Wayside Zone design and train speed limits
  • COMMS BETWEEN: Wayside zone and locomotive, Wayside-wayside (proprietary msg)
  • STATUS: In service – being expanded(as of 2012), currently approved for 110 mph operation
Integrated Services Digital Broadcasting—Terrestrial (ISDB-T)ISDB-T (Integrated Services Digital Broadcasting – Terrestrial) is a new type of digital broadcasting system for providing audio, video and multimedia services. ISDB-T system was standardized at the Association of Radio Industries and Businesses (ARIB) in Japan. ISDB-T uses a modulation method referred to as Band Segmented Transmission (BST) OFDMOrthogonal Frequency-Division Multiplexing.
Interoperable Electronic Train Management System (I-ETMS)
  • System being used by all 7 class I RRs for FRA required PTC
  • Current plan is for about 60,000 miles to be equipped.
  • Also being used by commuter lines Metrolink, San Diego North County, likely to be used on TRE (DART) and others.
  • Vital onboard and wayside designs.
  • Primary vital communication is between Onboard & Wayside.
  • Radio is specific design ordered by the RRs (BNSF, UP, CSX, NS) who own the vendor.

  • SUPPLIER(s): Wabtec, MeteorComm, plus other suppliers for Wayside logic
  • STRUCTURE: Proprietary “ITCNet”, OSI 7 layer TCP/IP
  • MESSAGING STD: ITC AAR Standard, Class D messages, Edge Message Protocol (EMP)
  • MAX BIT RATE: determined by radio (TCP/IP is 10 Mbps)
  • FREQ BAND: 220 MHzMegaHertz (MHz) 10^6 Hz
  • RADIO MFGR: MeteorComm
  • COMMS BETWEEN: Wayside and Vehicle; Office and Vehicle
  • STATUS: Currently being implemented (2015)
Link 16
  • Link 16 is a military tactical data exchange network used by NATONorth Atlantic Treaty Organization and nations allowed by the MIDS International Program Office (IPO)
  • Part of JTIDS/MIDS (STANAGNATO Standardization Agreement (STANAG), defines processes, procedures, terms, and conditions for common military or technical procedures or equipment between the member countries of the North Atlantic Treaty Organization (NATO). 5516)
  • Defined in MIL-STD-6016
  • Frequency: 960–1,215 MHzMegaHertz (MHz) 10^6 Hz
  • TDMATime Division Multiple Access-based
  • Can use FHSS?
  • Data rate: 31.6/57.6/115.2 kbpsKilobits per second (kbps)
Mark IV/V/VIA digital format that supports tone, numeric, and voice paging. This system requires 2ms to send a binary 0 and 4ms to send a binary 1 making the data transmission rate between 250 to 500 bpsBits per second (bps). Mark IV could handle tone only and Mark V and Mark VI could handle up to 10 digits.
MediaFLOMediaFLO was a technology developed by Qualcomm for transmitting audio, video and data to portable devices such as mobile phones and personal televisions, used for mobile television. In the United States, the service powered by this technology was branded as FLO TV. The "FLO" in MediaFLO stood for Forward Link Only, meaning that the data transmission path is one way, from the tower to the device. The MediaFLO system transmitted data on a frequency separate from the frequencies used by current mobile telephone networks. In the United States, the MediaFLO system used frequency spectrum 716-722 MHzMegaHertz (MHz) 10^6 Hz, which had previously been allocated to UHFUltra High Frequency (300-3000 MHz) TV channel 55.
Multiple sub-Nyquist Sampling Encoding (MUSE)
Multiplexed Analogue Components (MAC)
NEC/D3A digital encoding format developed by NEC America that supports tone only and numeric pages at a rate of 200bps. This format was developed for use in NEC R3-D3 pagers. This format uses 2 methods for preserving battery life. First a preamble is used to alert ALL pagers that there are incoming messages. Pagers remain idle till preamble detection. Second, pagers are grouped by address into 1 of 4 different groups. Each group is transmitted during a fixed time period and pagers only power up to look for its own address during the time its group is transmitted. Error correcting codes and even parity bits are used on each address and message.
Narrow-Bandwidth Television (NBTV)
Near Field Communication (NFC)

NexNet is a proprietary two way paging system designed by Nexus Telecommunications Ltd. of Israel. It utilizes spread spectrum technology integrated into their paging receivers to transmit response messages. In its initial implementation, messages are forwarded to pagers through the utilization of the POCSAG protocol. The additional messaging information required for time synchronization of the transmitted messages with the two way pager responses sent at a later time, as well as the transmission of two way paging control data, is imbedded within standard POCSAG output data. NexNet outbound data in support of two way paging is sent in such a way as to be totally transparent to normal POCSAG transmissions so that two way paging may coexist in any preexisting one way paging system.

The Nexus two way paging device, known as the Twager™, sends responses formatted according to the NexNet™ "uplink" protocol specification. In the Spread Spectrum technique, the data is transmitted over a range of different frequencies and is detected by receiving equipment located throughout the coverage region. Each Twager™ utilizes different sets of frequency combinations (frequency hops)when transmitting their data. Complete response messages may be recovered at receivers even though some portions of the response message may have been corrupted. This is because a message segment which is corrupted because of interference from other transmissions or by a simultaneous transmission from another Twager™ at one or more frequencies, has a high probability of being properly received at other frequencies over which this segment is transmitted.

In order to simplify the reception of the spread spectrum frequency hopped signals, the transmissions from the Twagers™ are required to synchronize to a precise clock. This precise time synchronization is achieved through the transmission of precision timing data which is imbedded in the POCSAG output stream. But, this is accomplished in a manner which permits this data to be overlaid into existing paging networks without the need to add any specialized transmission equipment.
North American Joint Positive Train Control (IDOT PTC)
  • Also known as North American Joint PTC (NAJPTC) demonstration.
  • Started in 1995 with Southern Pacific, ARINC and CANAC using ATCS design.
  • Led by FRA, contracted to TTCI as client systems engineer and LMCo as supplier.
  • Wayside centric system – train profiles sent from “zone controller ” computer server, onboard database limited in scope. Digital distribution of bulletins and authorities planned.
  • Onboard equip subcontracted to Wabtec.
  • Operate standalone on prior dark territory (virtual signaling) and as overlay on CTC.
  • Intended to demonstrate vital operation with high speed passenger & freight.
  • Advanced crossing activation by ITCS and quad gates – some crossing eliminations, all to support 110 mph passenger operations.

  • SUPPLIER(s): Lockheed Martin with Wabtec Onboard
  • STRUCTURE: ISO 7 Layer, Synchronous HDLC-LAPB
  • MAX BIT RATE: 9600 Bits/sec
  • FREQ BAND: VHFVery High Frequency (30-300 MHz)
  • COMMS BETWEEN: Train to Wayside Zone Controller
Positive Train Separation (PTS)
  • Followed ARES for BN (BNSF), added UP as a partner
  • Part of large scale GE-Harris development of optimized train movement mgmt. system
  • Collision prevention # 1 goal
  • Used Differential GPS for location
  • Radio portion: satellite two-way communication
  • Demonstrated on Oregon/Washington (Portland area) mainlines - 800 miles planned per news articles

  • FREQ BAND: UHFUltra High Frequency (300-3000 MHz)/VHFVery High Frequency (30-300 MHz)
  • RADIO MFGR: Rockwell ??
  • COMMS BETWEEN: Wayside and train
  • STATUS: Demonstration discontinued in Oregon/Washington in 2000.

REACH 11th root of 2 Selcall
RECEPTORAn FMFrequency Modulation subcarrier system developed by Seiko Tele- communications Systems, Inc. The systems uses the 64kHz subcarrier on commercial FMFrequency Modulation broadcasts and operates with a data rate of 19kbps. The system offers a variety of services including paging, sports, weather reports, and stock quotes through the Seiko MessageWatch. The system is currently in limited use in the US with expansion planned into the top 20 US markets.
Radio Code Line*Replaced pole-to-pole wiring along railroad between signal locations.
  • Non-vital supervisory data link (R/Link by Safetran as example)
  • FSKFrequency-Shift Keying/FMFrequency Modulation at 160 MHZ, UHFUltra High Frequency (300-3000 MHz), or 900 MHzMegaHertz (MHz) 10^6 Hz.
  • Transmitted code system control messages and indication messages via RFRadio Frequency carrier between office and field location (wayside).
  • Operated from 300 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. to 4800 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second.
  • Vital data was carried in coded AF track circuits.
  • Later versions (HD/Link by Safetran) used ATCS-200 messaging protocol to send vital data between field locations by radio. HD/Link radio was spread-spectrum low power.
  • Also used to relay AEI data and wayside detector data to signal locations.
Radio Mail Protocol (RAMP)RAdio Mail Protocol. This is the two-way version of the APOC radio paging protocol, which which it is backwardly compatible.
Sirius Satellite Radio
Swedish MBSAn FMFrequency Modulation subcarier system developed by the Swedish Telecommunications Administration. This paging format supports tone-only, numeric and alphanumeric paging. Data is transmitted using the 57kHz subcarrier at a rate of 1187.5 bpsBits per second (bps). MBS (Mobile Search) is used in a modified form (MMBS) in the US by Cue Paging.
Voice Inversion Scrambling
Wide Area Augmentation System (WAAS)The Wide Area Augmentation System (WAAS) is an air navigation aid developed by the Federal Aviation Administration (prime contractor Raytheon Company) to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability. Essentially, WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including precision approaches to any airport within its coverage area.