ARLA/CLUSTER: Novo modo em banda estreita para as bandas de 2200, 600 e 160m

[João Gonçalves Costa]

[http://www.qsl.net/zl1bpu/CMSK/VK2DDIcmsk.jpg]
New narrow-band mode for LF/MF released

Con Wassilieff ZL2AFP has recently released a new narrow-band digital mode, CMSK, designed specifically for the LF and MF ham radio bands (2200, 600 and 160m).

The mode uses MSK modulation, familiar to LF and MF listeners as the mode most used by commercial and military transmissions. One major advantage of MSK is that unlike PSK, it does not require linear amplification to maintain narrow bandwidth.

The new ZL2AFP CMSK mode can be described as Correlated, Convolved Minimum Shift Keying, and uses a full-time NASA standard convolutional coder with a generous interleaver to provide impressive QRN resistance.

Synchronism is assured, even on very weak signals, by a transmitted PN-sequence frame marker and cross-correlator at the receiver.

Four modes have been provided, from 125 baud (<200Hz bandwidth, 60 WPM) down to 7.8 baud (12.5Hz bandwidth, 4WPM). The narrowest and slowest mode is intended for beacon applications, and can be received 100% at -21dB S/N in 3kHz bandwidth. The default mode, CMSK63, has been reliably copied across the Tasman, at a range of 2200km on 600m from a transmission well under 1W EIRP.

Software for this new mode is now available from
www.qsl.net/zl1bpu/CMSK/cmsk.htm<http://www.qsl.net/zl1bpu/CMSK/cmsk.htm>, where a description of the design is also given.

Murray Greenman ZL1BPU/ZL1EE
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