PSK31 Etc De G4UCJ Et De Celle De ZL1BPU Digital Modes

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PSK31 Etc De G4UCJ Et De Celle De ZL1BPU Digital Modes mp-ref-novembre-g4-2 9/11/05 15:42 Page 33 RADIO-REF N°782 - novembre 2005 > Les modes digitaux et autres MGM en HF Traduction et adaptation par F1ULT, Pascal BIMAS, de la page Digital avec un débit double par rap- Modes-PSK31 etc de G4UCJ et de celle de ZL1BPU Digital Modes. port à celui du PSK31 normal. Il est donc bien adapté pour le Cet article comporte les descriptions simples de certains modes digitaux, bavardage et les échanges des courants ou moins répandus et de plusieurs nouveaux modes, ainsi que de contests. Les inconvénients de ce mode sont l'élargissement modes plus anciens et dont certains sont devenus très peu utilisés de nos de la bande passante nécessai- jours. L'abréviation MGM signifie Machine Generated Modulation et re par rapport au PSK31, l'aug- désigne les modes où l’ordinateur est le composant essentiel pour émettre mentation de la puissance et recevoir (par exemple PSK31, SSTV,…) que le mode soit de type digital, nécessaire pour conserver le analogique ou mixte. Certains termes techniques seront employés. même niveau de copie qu'un Avec un peu de chance, vous les trouverez définis dans le glossaire à la fin signal PSK31 et le fait que les logiciels de décodage ne le de l’article. supportent pas encore tous. Le PSK63 peut être identifié assez IDENTIFICATION VISUELLE PSK31, PSK63 et autres variantes facilement car il ressemble à un DES DIGIMODES : ’gros’ signal PSK31. Que ce soit en HF ou au-des- 1 sus, les modes digitaux devien- 4 D'autres variantes du PSK31 nent de plus en plus populaires Un signal BPSK31 ‘propre’. existent comme le PSK16 sur les bandes radioamateurs. C'est comme cela que votre signal devrait apparaître ! (bande passante/vitesse réduite De nouveaux modes sont déve- de moitié par rapport au loppés tout le temps et se tenir PSK31), le PSK125 (4 fois la au courant de ces dernières bande passante/vitesse) et technique nouveautés devient un boulot à 2 d’autres variantes expérimen- plein temps ! L'un des princi- tales (le PSK220 de F6CTE par paux problèmes rencontrés par exemple). La variante la plus le nouveau venu aux modes Signal BPSK31 déformé d’une manière détestable. usitée du BPSK31 est le digitaux (également désignés QPSK31, qui est dépendant de par le terme "digimodes") est de la bande latérale utilisée (c'est- savoir comment identifier ce 3 à-dire que l'émetteur et le qu'il voit et écoute. La plupart récepteur doivent obligatoire- des logiciels de décodage utili- Plusieurs QSO en PSK dans un minimum de ment employer la même bande sent un affichage visuel type bande. latérale). Cependant QPSK31 ‘cascade’ pour faciliter un n'est pas utilisé de manière 4 accord pratique. C'est avec courante en dépit de ses capa- cela à l'esprit que je suis allé cités de décodage supérieures sur les bandes et que j'ai pris lors de conditions médiocres. des images des modes digitaux les plus courants en usage en Signal PSK63 reçu entre les USA et le Canada sur 20 m. 5 La Slow Scan TV (Télévision ce moment. Ci-dessous vous à balayage lent) est très popu- verrez les captures d'écran de laire depuis des années ; la chaque mode accompagnées vaste majorité de la SSTV est de de quelques commentaires nos jours générée par ordina- succincts sur le mode. Les PSK31 - PSK63 teur. Les modes les plus utilisés images montrent la variante la ce signal. Constatez qu’à cer- kHz approximativement). Il est sont le Martin et le Scottie. Le plus répandue du mode, bien tains endroits du signal adja- plutôt courant de voir 15 Robot reste encore employé. La que certains digimodes possè- cent signal sur la gauche, le signaux ou plus sur un afficha- plupart des programmes SSTV dent plusieurs ‘parfums’ ! signal distordu est suffisam- ge cascade sur une largeur de supportent ces modes et bien ment large pour occasionner 2,5 kHz. d'autres aussi. Les images 1 Voici un signal BPSK31 des interférences à l’autre. reçues sont recomposées ligne déformé d’une manière détes- 3 Le PSK63 est en train de par ligne après une attente table. Le phénomène est proba- 2 Parce que le PSK31 a une gagner en popularité, étant d'environ une minute, par blement provoqué par une largeur de bande de seulement donné que beaucoup de pro- conséquent vous devrez vous saturation à l'émission. Réduire 31 Hz, beaucoup de signaux grammes supportent mainte- montrer patient ! La qualité le niveau de l’entrée en RX ou peuvent loger dans la même nant ce mode. L'avantage offert peut être très bonne même de la sortie en TX de la carte largeur de bande qu'aurait par celui-ci est que les don- après avoir traversé de longues son améliorerait la qualité de occupée un signal SSB (2,4 nées sont envoyées et reçues distances comme trajectoire. 33 mp-ref-novembre-g4-2 9/11/05 15:42 Page 34 technique 6 Voici deux images reçues : SSTV (Slow Scan TV) En raison de sa bande passante celle de gauche vient d'Hawaï assez large, le MT63 est habi- et celle de droite de Suède. tuellement confiné sur le 14 5 MHz et au-dessus, où il y a suf- Signal SSTV 7 C'est le mode digital ‘origi- fisamment d'espace pour le nel’. Le RTTY a été populaire à loger. 6 travers le monde entier depuis KH6AT de Hilo à des années et il l’est toujours Hawaï reçu sur une 10 Hellschreiber (ou Hell, abré- malgré la progression du PSK31. bande bruyante par viation sous laquelle ce mode DF4CK. Au début, la seule manière Réception parfaite de est plus communément connu) d'opérer en RTTY était de se SM7UZB en Suède. est un peu différent des autres servir d'un terminal électromé- modes. Lors de la réception canique comme un de ceux d’un signal Hell, ce sont vos Réception personnelle des séries Creed 7, Siemens, d'une image de yeux qui font le filtrage ! Le Teletype et autres SAGEM , qui F6AYD et une autre de texte décodé est affiché sur étaient encombrants, bruyants F5PNS lors du QSO l'écran sous la forme virtuelle et salissants. De nos jours, pra- francophone hebdoma- d'une bande de téléscripteur daire sur 3,733 MHz tiquement tout le RTTY est vers 9 h locales. (support original) qui se dérou- généré et décodé par l'associa- le (comme illustré par cette tion de la carte son et de l'ordi- SSTV capture d'écran). Le Hell a une nateur. Les radioamateurs utili- RTTY (Radio Télétype), MFSK, MT63, HELLSCHREIBER (HELL) sonorité très distinctive ‘grin- sent le 45 bauds (rapidité de PACKET, PACTOR, THROB, çante’ et c'est un mode à bande modulation) avec un shift de étroite. Le signal Hell se trouve 170 Hz. 7 sur la gauche de l'image (avec Les stations commerciales Les deux bandes d’un signal le petit drapeau vert juste au- emploient le 50 ou le 100 RTTY correspondant au MARK et dessus), avec un signal MFSK bauds avec des shifts de 425 ou au SPACE. sur la droite—notez que la même 850 Hz. La plupart des bande passante occupée par le logiciels proposent des réglages 8 signal MFSK est beaucoup plus pour paramétrer ces différents large en comparaison avec le vitesses et shifts. signal Hell. Même de faibles signaux peuvent être décodés 8 Le MFSK est analogue au sys- Signal MFSK, un mode de plus puisque la combinaison de en plus populaire. tème commercial Piccolo. Il est votre vue et de votre cerveau très bon lors de conditions de pourra ‘remplir les blancs’ propagation pauvres. La lorsque le signal s'atténuera. variante usuelle du MFSK est Plusieurs variantes ont été 9 le MFSK 16, mais d'autres développées autour de ce mode : Signal MT63 types tels que le MFSK 8 sont le FM-Hell, le PSK-Hell, le en développement et expéri- Duplo-Hell, le S/MT-Hell, le mentation, à côté d'autres 10 C/MT-Hell, le Hell 80 et le modes comparables au MFSK Signal Hell(schreiber) Slow FELD. comme Domino ou bien OLI- VIA. Le MFSK est dépendant de 11 11 Les boîtes aux lettres HF et la bande latérale, dès lors vous Signal PACKET Radio. autres systèmes utilisent le devrez avoir votre récepteur PACKET pour acheminer des réglé sur la bande latérale cor- messages aux utilisateurs. Le recte afin de le décoder conve- 12 débit de données habituel en nablement. L'accord est égale- HF est de 300 bauds, alors que Signal PACTOR. ment très critique, quoique le 1200 et le 9600 bauds pren- l'AFC aide quelque peu. nent place en VHF et en UHF. 13 L'illustration montre une boîte 9 Le MT63 est très robuste et aux lettres/BBS en Turquie offre une réception à 100% échangeant avec un autre BBS quand d'autres modes flan- Signaux au Royaume Uni. Le flux court chent. Les compromis toutefois THROB. de données en bas de l'image sont la largeur de la bande et la correspond à l’information rapidité. Le MT63 est assez lent contenant l'en-tête et l'indicatif et occupe une plage de 500 Hz alors que le flux plus long qui jusqu'à 2 kHz (cela reste tout suit concorde avec les véri- de même inférieur à la bande tables données. Plusieurs de occupée par la phonie). ces BBS/boîtes aux lettres PAC- RTTY; MSFK, MT63... 34 mp-ref-novembre-g4-2 9/11/05 15:42 Page 35 RADIO-REF N°782 - novembre 2005 KET peuvent être entendus cré- JT6M, DOMINO, FAC-SIMILE (FAX) définis (0 ou 1 par exemple), à pitant aux alentours de 14,1 l’opposé des modes analo- MHz.
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