Automatic link establishment

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Automatic Link Establishment, commonly known as ALE, is the worldwide de facto standard for initiating and sustaining High Frequency radio communications. ALE is a feature in an HF communications transceiver system, that enables the station to make contact, or initiate a circuit, between itself and another HF radio station or network of stations. The purpose is to provide a reliable rapid method of calling and connecting during constantly changing HF ionospheric propagation, reception interference, and shared spectrum use of busy HF channels. It can be used with or without highly skilled radio operators, through the benefits of processor control, but generally takes some operator training to understand how to operate it.

The ALE system enables operators to connect for voice, data, text, instant messaging, or image. A radio operator initiating a call, can within a few minutes, have the ALE automatically find and pick an HF frequency that is optimum for both sides of the communication link. It signals the operators audibly and visually on both ends, so they can begin communicating with each other immediately. In this respect, it can eliminate the longstanding need for repetitive calling on pre-determined time schedules and tedious monitoring static on HF. It is useful as a tool for finding optimum channels to communicate between stations in real-time, while totally avoiding guesswork, propagation beacons, and complicated HF prediction charts altogether. ALE is most commonly used for hooking up operators for voice contacts on SSB (single sideband modulation), HF internet connectivity for email, SMS phone texting or text messaging, real-time chat via HF text, Geo Position Reporting, and file transfer. High Frequency Internet Protocol or HFIP may be used with ALE for internet access via HF.

ALE techniques include automatic signaling, selective calling, automatic handshaking, and automatic station identification. Other automatic techniques that are related to ALE are channel scanning and selection, link quality analysis (LQA), polling, sounding, message store-and-forward, address linking protection, and anti-spoofing. Optional ALE functions include polling and the exchange of orderwire commands and messages. The orderwire message, known as AMD Automatic Message Display, is the most commonly used text transfer method of ALE, and the only universal method that all ALE controllers have in common for displaying text.

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[edit] Automatic Link Establishment Standards

The common basic protocol standards for ALE are MIL-STD 188-141 and FED-1045, known as 2nd Generation or 2G ALE or 141 ALE. 2G ALE uses non-synchronised scanning of channels, and it takes about several seconds to half a minute to repeatedly scan through an entire list of channels looking for calls. Thus it requires longer duration calls to connect or link with another station that is unsynchronised with its calling signal. The vast majority of ALE systems in use at the present time (edited in mid-2008) are 2G.

Newer standards of ALE use accurate time synchronisation via GPS-locked clocks to achieve faster and more dependable linking, and these are generally known as 3rd Generation or 3G ALE. Through synchronisation, the calling time to achieve a link may be reduced to less than 10 seconds. Although 3G ALE is better and more reliable, the existence of a large installed base of 2G ALE radio systems, and the wide availability of equipment, has made 2G the baseline standard for global interoperability.

The more common 2G ALE signal waveform is designed to be compatible with standard 3 kHz SSB narrowband voice channel transceivers. The modulation method is 8ary Frequency Shift Keying or 8FSK, also sometimes called Multi Frequency Shift Keying MFSK, with eight orthogonal tones between 750 and 2500 Hz. Each tone is 8 ms long, resulting in a transmitted over-the-air symbol rate of 125 baud or 125 symbols per second, with a raw data rate of 375 bits per second. The ALE data is formatted in 24-bit frames, which consist of a 3 bit preamble followed by three ASCII characters, each one 7 bit long. The receive decoder is usually done by Digital Signal Processing techniques and can decode the 8FSK signal at a negative signal to noise ratio, meaning it can pull the signal out when it is below the noise level.

[edit] Automatic Link Establishment in amateur radio

Amateur radio uses an Automatic Link Establishment ALE open network. Amateur radio has developed a flavor of 2G ALE called Ham-Friendly ALE, that utilizes the common denominators of ALE protocols, enabling any manufacturer's radios or software to be utilized for interoperative communication and networking. To establish 2-way radio-communications, it uses a combination of active ALE on data channels, and passive ALE on voice channels. The active ALE includes periodic sounding (station identification), while passive ALE uses no sounding.

Each amateur radio ALE station uses the operator's callsign as an address in the ALE controller. When not actively in contact with another station, each HF SSB transceiver constantly scans through a list of ALE frequencies called channels, listening for its callsign. To reach a specific station, the caller simply enters the callsign just like dialing a phone number. The ALE controller selects the best available frequency that is not busy, and listens to it before it sends out brief selective calling signals containing the callsigns. When the distant scanning station detects the first few characters of its callsign, it stops scanning and stays on that frequency. The two stations' ALE controllers automatically handshake to confirm that a link is established and they are ready to communicate. The receiving station, which was muted up until now, will typically emit an audible alarm and visual alert for the receiving operator of the incoming call. It also indicates the callsign of the linked station. The operators then can talk in a regular conversation.

[edit] Amateur radio Automatic Link Establishment network

The Channel List for ham radio ALE High Frequency is frequency coordinated with all IARU Regions (International Amateur Radio Union) for international, regional, and local use in the Amateur Radio Service. All Amateur Radio ALE channels use "USB" Upper Sideband. All channels are subject to the different rules, regulations, and bandplans of the region and local country of operation. Some channels or modes in the frequency list may not be available in every country, but there are primary and global channels in common with most countries. The amateur radio Automatic Link Establishment system is an open, so it enables all amateur radio operators and amateur radio nets worldwide to participate in ALE and share the same ALE channels. Amateur radio operators may use it to call each other for voice or data communications. Hot standby nets are in operation 24/7/365 for International Emergency and Disaster Relief. The Ham Radio Global ALE High Frequency Network is the world's largest open ALE network for internet connectivity.

CH# Frequency kHz Sideband Common Use Description
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01- 1806.0 USB VOICE/DATA 
02- 1840.5 USB VOICE/DATA 
03- 1845.0 USB VOICE/DATA International Emergency/Disaster Relief 
04- 1996.0 USB VOICE/DATA 
05- 3584.5 USB DATA/VOICE 
06- 3596.0 USB PRIMARY DATA Internet connectivity, sounding
07- 3617.0 USB DATA/VOICE 
08- 3626.0 USB DATA/VOICE
09- 3791.0 USB VOICE International Emergency/Disaster Relief 
10- 3845.0 USB VOICE 
11- 3996.0 USB VOICE 
12- 5371.5 USB VOICE (Emergency Only)
13- 5403.5 USB VOICE (Emergency Only)
14- 7040.5 USB DATA 
15- 7065.0 USB VOICE 
16- 7099.5 USB DATA 
17- 7102.0 USB PRIMARY DATA Internet connectivity, sounding
18- 7110.5 USB DATA 
19- 7185.5 USB VOICE International Emergency/Disaster Relief 
20- 7296.0 USB VOICE 
21- 10136.5 USB DATA/VOICE 
22- 10142.5 USB DATA 
23- 10145.5 USB PRIMARY DATA International Emerg/Relief, Internet connectivity 
24- 14100.5 USB DATA 
25- 14109.0 USB PRIMARY DATA Internet connectivity, sounding
26- 14112.0 USB DATA 
27- 14342.5 USB VOICE 
28- 14346.0 USB VOICE International Emergency/Disaster Relief 
29- 18104.5 USB DATA 
30- 18106.0 USB PRIMARY DATA Internet connectivity, sounding
31- 18117.5 USB VOICE/DATA  International Emergency/Disaster Relief
32- 18157.5 USB VOICE 
33- 21096.0 USB PRIMARY DATA Internet connectivity, sounding
34- 21116.0 USB DATA 
35- 21437.5 USB VOICE International Emergency/Disaster Relief 
36- 24926.0 USB PRIMARY DATA Internet connectivity, sounding
37- 24932.0 USB VOICE International Emergency/Disaster Relief 
38- 28146.0 USB PRIMARY DATA Internet connectivity, sounding
39- 28312.5 USB VOICE/DATA  International Emergency/Disaster Relief
40- 28327.5 USB VOICE  
41- 50162.5 USB VOICE/DATA 
42- 144162.5 USB VOICE/DATA

Amateur Radio ALE standards:

1. ALE System = MIL-STD 188-141 ; FED-1045 (8FSK, 2kHzBW)
2. Call or Sounding transmission duration: Optimum 22 seconds. Maximum 30 seconds.
3. Scan rate: 1 or 2 channels per second.
4. Sounding Interval = 60 Minutes or more (for same channel)
5. Digi Texting Audio Centre Frequency= 1625HZ
6. Universal short text messaging standard = AMD (Automatic Message Display)
7. TWS Sounding (This Was Sound)

Amateur Radio open ALE NETs:

1. HFL = All voice stations, open selective calling (10 member slots)
5. HFN = Ham Radio Global ALE High Frequency Network (10 member slots)
4. QRZ = Open calling on all channels (3 member slots)
2. GPR = Geo Position Reporting (3 member slots)
3. RPT = Station Status Reporting(3 member slots)

Info: This listing is current as of April 2008. For more information about Amateur Radio ALE Automatic Link Establishment and updates of this channel list please see the website: HFLINK.COM

[edit] References

[edit] See also

MFSK