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Three South African amateurs made what is believed to be the first successful transmission of a Digital Voice signal over HF amateur bands in the country. The Digital Voice signal was transmitted at 11:16 am on Sunday 8 August by Andrew Roos ZS1AN and received by Dennis Wells ZS1AU with technical assistance from Ettienne Vosloo ZR1AHW. The transmission took place on the 10m band, with an occupied bandwidth of approximately 2.3 KHz.
On Tuesday 10th August, Dennis and Andrew successfully exchanged signal reports on the 15 metre, completing the first known digital voice QSO in South Africa. The QSO was monitored by Sean White, ZR1BSD.
Digital voice is a new mode where speech is converted to digital data using a low-bitrate vocoder. The digital data is then transmitted using a high-speed modem, and the digital data is decoded to recover the audio at the receiver. Although still in the experimental stages, there is worldwide interest in Digital Voice, which can deliver very high signal-to-noise ratios over medium quality SSB channels.
The software used in this experiment was HamDream version 2.4, which is an open-source implementation of the Digital Radio Mondiale broadcasting standard that has been adapted for amateur use by HB9TLK. It can be downloaded free of charge from the SARL website, www.sarl.org.za. For more information, see HB9TLK's website, www.qsl.net/hb9tlk.
All you need to explore this fascinating new mode is a PC with a full-duplex soundcard, a soundcard/rig interface like those used for PSK-31 and similar digital modes, and a PC headset and microphone that can be purchased at any computer store for about R 100. So get QRV on digital voice and join the fun! Andrew and Dennis are keen to make contact with other divisions using this exciting new mode. If you would like to arrange a sked please send email to Andrew, [email protected] or Dennis, [email protected].
Andrew will be giving a talk on Digital Voice at the SARL "Radio Technology in Action" Hamfest at the National Amateur Radio Centre in Johannesburg on 21st August - see you there!