The ABC has successfully broadcast what is likely to be the first standard DRM (Digital Radio Mondiale) signal transmitted in Australia.
DRM, as reported last month on radioinfo, is a digital broadcast technology compatible with standard AM frequencies, and could be useful in Australia to bring digital radio to regional areas more cheaply than the Eureka system, which is expected to be used in capital cities.
On Saturday 11 June, Mathew Magee of the ABC’s T&D Transmission Network Services broadcast the signal. Magee has been receiving European and US DRM shortwave broadcast transmissions for about two years, and has put considerable effort into receiving, and now transmitting DRM signals.
In his report on the experiment, Magee says:
The open-source ‘DReaM’ software project started out to build a DRM demodulator, that would take 12kHz IF into the soundcard of a standard PC and decode audio. It has reached a very good level of capability in this regard, currently supporting all radiation modes, AAC+SBR audio decoding, several multimedia service types. It also provides extensive signal analysis capability and logging.
Decoding of other DRM audio formats (such as CELP) is a work in progress. Development of the modulation capability has also been progressing, slowly, but has now reached a stage where it can be used for transmission experiments.
The main purpose of the significant work is to investigate the use of an existing analogue HF transmitter in radiating a DRM signal.
For this test, the DRM signal was generated as a ‘real’ IF at 12kHz, and fed into the modulator/converter chain at the same point an AM signal would normally go. All of the normal AM signal pre-processing was bypassed and DRM IF fed
straight into this modulator. A frequency of 24,975kHz was used for testing.
Three receivers were used: Watkins-Johnson 8709, a Fraunhofer software receiver and Icom IC-R10 portable receiver.
The results of Magee’s experiment revealed some traps in various transmission and reception setups. The information gained will be useful to the ABC, and indeed all radio sectors as they plan for the implementation of digital radio transmission nationwide.