ARLA/CLUSTER: Nova modalidade digital em 13 kHz obtém sucesso nas comunicações transatlânticas

[João Gonçalves Costa]

New data mode crosses Atlantic on 136Khz at the first attempt

Running no more than 400 watts to a 12 meter top loaded vertical , with a carrier frequency of 137.5 Khz, estimated ERP of no more than 250 mW, Gary G4WGT using the new 'OPERA' data system successfully transmitted a signal to Joe VO1NA, at a range of 3500 Km .
Joe completed Six decodes of Gary's full call in a period of 2 hours, the first being at 21:43z, unexpectedly early in the night.

In contrast, using the established very slow cw QRSS and visual spectrum decoding, at QRSS 60, the call sign "G4WGT" will take 54 minutes to send, and would need to be visible on the plot. The 136KHz version of Opera taking only 8 ,or 31 minutes at enhanced s/n performance , the 500 Khz coding taking 2 or 15. Minutes

The OPERA mode was envisaged by Graham G0NBD, as a way of providing data operations for stations who had only the capability of CW operation, to date, all data modes required the modulation of the transmitted carrier, either by frequency, phase or amplitude changes. This was to only use off/on keying.

Outlining the idea to J Ros, EA5HVK author of the now established ROS Data mode, Jose Ros, after some email exchange's, in turn took on the coding of the mode, using DSP techniques he had refined during the development of the ROS data mode and produced a complete windows compatible Tx/Rx package with internet spotting and chat facility, with com-port keying and audio tx drive. Far exceeding the original 'idea'!

Initial testing was conducted on the 500Khz experimental band, with G0NDB and G4WGT, later other stations joined the test group and Gus SM6BHZ made successful 136 transmissions using the then OP65 mode.

Opera encodes the data and keys the transmitter with a sequence of variable length 'dots and dashes' extend out along a time line, with surprising results, the 2 minute version achieving a s/n performance similar to the established WSPR system and the longer versions are capable of many dB's lower.

Reception is facilitated in the normal 'data' way of taking audio from the receiver and decoding with software, decoding may take place with up to 33% data loss , development continues at a pace and the most up to date info can be found http://groups.yahoo.com/group/O_P_E_R_A_/, OPERA is now listed as a mode on the PSK-Reporting map

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