ARLA/CLUSTER: HFLink - Automatic Link Establishment

[João Gonçalves Costa]

Prezados Colegas,

Mais uma vez os radioamadores americanos, com destaque para a grande especialista aposentada do Exercito Norte-Americano, Bonnie Crystal-KQ6XA, não param e já se encontra desde 26 Junho passado, em franco desenvolvimento um sistema automático global de comunicações de emergência, e não só, recorrendo a um software aberto muito parecido com o que usam os militares e algumas ONG`s em HF á bastantes anos.

Basicamente, o software ALE-Automatic Link Establishment assenta em 42 canais pre-seleccionados distribuídos pelas diferentes bandas de amador entre os 160m e os 2m, sendo 9 desses canais globais e em HF. O programa versátil permite manter uma rede global ou local, sendo as frequências seleccionadas automaticamente em função das condições de propagação, distancia, ruido,tipo de msg,antenas disponiveis, etc.

O operador não procura qual a melhor frequência para o contacto, esta é seleccionada automaticamente pelo software que realiza um scanner continuo pelos canais e avalia permanentemente as condições em função das msg que são necessárias enviar. Como sabemos, realizar contactos por voz ou em PSK31 não é a mesma coisa, nem são necessários os mesmos requisitos técnicos 

Assim, a preocupação constante de procurar uma frequência nas diferentes bandas, recorrendo a previsões de propagação, a beacons, etc, onde existam condições hipoteticas para o contacto deixa de ser importante, o sistema encarregasse de seleccionar este importante parâmetro sem o qual não é possível estabelecer comunicações. 

O transceptor administrado pelo sistema procura constantemente e em tempo real manter a rede interligada ou o contacto ponto a ponto sem que os operadores tenham de procurar. Basicamente todos os transceptores que possam ser controlados via PC podem ser usados, no entanto, existem alguns modelos onde é mais facil a integração, exemplos:

ICOM
IC746, IC746PRO, IC7400, IC756PRO (Milspec 1030E-DSP), IC756PRO2, IC756PRO3, IC765, IC775, IC781, IC7800 (
  
KENWOOD
All Kenwood models after, but excluding the TS-440, PA relays handled by use of SPLIT VFO, all support up to 2 ch/sec scan rate, newer models at 9600 baud up to 5 ch/sec and those at 19,200 baud at 10 ch/sec scan rate
  
YAESU
FT-920, FT-990 with SPLIT VFO (FT-890 with special QS/S modification) all can do up to 2 ch/sec scan rate

Neste momento a rede Global ao nível dos EUA é contituida por 6 estações piloto automáticas trabalhando 24H e 7 dias por semana, equipadas com o sistema de scanning ALE, Antenas multibanda e um software especial de controlo, que pode ser comandado e acedido via Internet.

O sistema está em expansão constante com integração de novas funcionalidades, exemplo; msg tipo SMS aos membros enviadas da Internet, telefone móvel ou vice-versa. Os promotores esperam alargar rapidamente este projecto ao nível planetário.

Os requisitos básicos são:
- Um Computador, preferencialmente portátil.
- Um transceptor.
- Um conjunto de antenas multibanda comutadas ou comandadas automaticamente.(não pensem que é preciso ANTENAS DIRECIONAIS TIPO LOG-PERIÓDICA, ler a explicação e conselho mais abaixo dadas pela Bonnie Crystal-KQ6XA)  

Para mais informações podem aceder á página do HFLINK Group em: http://hflink.com/ . 

Entretanto, deixo-vos algumas explicações em inglês dadas pela excepcional Amadora de Rádio norte-americana, Bonnie Crystal-KQ6XA

João Costa
CT1FBF


What is ALE?
ALE is the humorous acronym for the lofty-sounding Automatic Link Establishment. It is the de-facto worldwide standard for initiating communications using High Frequency radio. HF radio conveys signals via ionospheric propagation, which is a constantly changing medium. With the capability to call up a specific station, a group of stations, a net, a networked station, or just CQ, ALE is a versatile system for connecting radio operators for voice, data, text, instant messaging, internet messaging, or image communications. A radio operator initiating a call, can within minutes have the ALE automatically pick a frequency that has a good propagation path. It signals the operators 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 monitoring static on HF radios. It is a great tool for finding optimum ionospheric propagation between stations in real-time, while avoiding guesswork, beacon listening, and complicated HF prediction charts altogether. These days, ALE is most commonly used for hooking up operators for voice communications on SSB and for internet messaging, but there are many other useful features.


How ALE Works
Each radio ALE station uses a callsign or address in the ALE controller.When not actively in communication with another station, each HF SSB transceiver constantly scans through a list of frequencies, 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 and 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. At the conclusion of the QSO, one of the stations sends a disconnect signal to the other station, and they each return their ALE stations to the scanning mode. Some military / commercial HF transceivers are available with ALE options. Amateur radio operators commonly use the PCALE soundcard software ALE controller, interfaced to a ham transceiver via RS-232 CAT port, multi-frequency antenna. 

Multi-Frequency Antennas Systems.
The Autotuner Inverted-V-Fan-Dipole and Autotuner V-Fan-Dipole
Design and Installation Notes by Bonnie Crystal KQ6XA

Background
Various versions of multi-wire dipole antennas are known and widely used. HF inverted-V antennas called "maypole" antennas, have been utilized with dipoles resonant in the amateur bands. The most common has been the 3.8MHz/7.1MHz resonant version fed with 50ohm coax. Technically, the antenna system consists of two or more dipoles of different lengths arranged radially in inverted-Vee form with a single common feedpoint. There are other configurations possible within the general category of "fan dipoles". 

Autotuner Problems with Single Wire Antenna
Autotuners have been in popular use for both amateur and non-amateur applications, especially when many channels or bands of frequencies are utilized throughout the HF spectrum. Problem frequencies are sometimes found in long single-wire autotuner installations, usually due to combined RF reference plane (tuner ground) and wire resonance resulting in a very high impedance presented to the autotuner. At the problem frequencies, it can take a long time for the autotuner to repeatably find a match, or it may not be possible for it to find an acceptable match. Other problems with the same root cause can lead to excessive RF radiation from the feedline at the transmitter (hot mic syndrome). Sometimes, simply changing the length of the antenna wire slightly is sufficient to move the "problem" to an unused frequency. But changes in the ground conductivity due to rain or other factors can bring the problem back.

Multiple Antenna Wires for Fast Autotuning
HF-ALE (Automatic Link Establishment) requires fast autotuner action, and the linking functions best when the antenna matching autotuning cycle is completed within a fraction of a second. Application of the multi-wire dipole principle to the autotuner installation provides a solution. In practice, it has been found that there are advantages to certain wire lengths or wire length ratios for autotuner use in the HF spectrum. These ratios of wire lengths present multiple "convenient" lower impedances to the autotuner at any given frequency, enabling it to achieve a matched condition rapidly and repeatably, thereby mitigating "problem frequencies". 

Autotuner Fan Dipoles in Use for ALE
I have developed the two successful versions of an autotuner fan dipole antenna system shown above, through both theoretical and empirical design (trial and error). I am presently using one of these antenna systems on the air 24/7 for ALE, from 1.8MHz to 28MHz. I am using an SG-230 autotuner in this installation, but the principles are the same for most of the common autotuners of similar type. 

Common Mode Chokes 
I've set up 3 different SGC autotuner systems at base stations using the common mode chokes (1:1 balun a misnomer) in the control/DC cables/feedlines, combined with a grounding strap to earth. These techniques keep some of the noise from computers and equipment in the station from being conducted into the autotuner's antenna system on receive, and they help choke off RF currents on transmit from going down the cables into the station. In the first two of those installations, severe RFI was eliminated that was present before the "chokes" were installed. In the third, I installed the chokes during the initial installation, and have not removed them to see how much difference they make.

Grounding
Indeed, many operators are content to simply ground the coax and control cable at the station entrance (good practice). I'm from ye olde school of lightning protection (having built broadcast stations and telephone central switching offices in my earlier career), so you will see additional ground straps present near the antenna in my base station antenna designs. I believe that a direct lightning discharge path to earth ground is a good design starting point for basic lightning protection. I also believe that the possible loss in RF efficiency at some frequencies is worth trading for the added safety that earth grounding at the antenna provides.

Temporary Portable Installations
For temporary portable installations when no chance of lightning hazard exists, the safety ground strap could be eliminated. The common mode chokes and control feedline ferrites may also be eliminated if no "hot mic" RF feedback or RFI is experienced.

Feedback and Field Reports Requested
There are other possible combinations of wire lengths and configurations that should function in a similar manner. I am interested in the results of others who are using this type of antenna system or derivatives of it. Feedback or field reports may be sent directly to the HFLINK or HFpack groups.

Bonnie Crystal KQ6XA