These transmissions currently include DAB and DAB+ services, together with text and slideshow services on the DAB signals.
CRA is happy to distribute samples of these test streams to receiver manufacturers to assist in product development. It should be noted that these test streams are samples of what is being broadcast now, and may not be exactly the same as our final broadcasts.
(For example, currently CRA are not broadcasting slideshow on DAB+ , but we will be doing os soon.)
CRA has a selection of multiplexers which are broadcasting as part of the Sydney trial. The output of the multiplexer is an Ensemble Transport Interface stream (ETI stream).
We are happy to forward this ETI file to those developing receivers.
To use this file to test receivers it is necessary to have an ETI replayer, and a COFDM modulator. These will generate a radio frequency signal which can be used to test receivers.
(The ETI replayer and COFDM modulator could be separate pieces of hardware, or could be software functions on the same device.)
The Ensemble Transport Interface (ETI) is usually presented as a 2 Mbit/s 75 ohm BNC connection (G.703). This contains DAB information and also headers and a large amount of padding.
The CRA Test stream is a bit for bit recording of an ETI stream, including all headers and padding bits. The files are typically ten minutes long and about 150 Megabytes in size. These are zipped down to form smaller files 50 Megabytes in size for sharing. Some of our files have a 1 kilobyte proprietary header at the start of each 150 Megabyte file if they have been recorded by Somerdata equipment.
The files are typically ETI (NI) format, without timestamps.
Our preferred method of distributing these files is sending them by the internet, using an FTP relay service.
In order to convert the ETI file into a 2 Megabit/second ETI stream an ETI replayer is required. This may typically take one of the following forms:-
• A PC with a hardware output card with a 2mbit/s G703 BNC output, such as the Somerdata DABSTOR (www.somerdata.com)
• A PC with a USB connected device with a 2 Mbit/sec G703 BNC output such as the Enensys DiviDual. www.enensys.com. It is listed as a DMB device.
It should be noticed that there is no difference in the structure between DAB+, DAB and DMB streams. Any ETI replayer can replay any of these.
The COFDM modulator converts the 2 Mbit/sec ETI stream into an RF signal.
Not all COFDM modulators produce RF – some may only produce a baseband I/Q output. It is important to have a COFDM modulator with an RF output.
Typically a COFDM modulator has a 75 Ohm G703 input connector to receive the ETI stream.
Once again, it should be noticed that there is no difference in the structure between DAB+, DAB and DMB streams. Any COFDM modulator which can work with any one of these formats will work with them all.
UBS Canada sell COFDM modulators. www.uniquesys.com
To get a copy of the test stream please email me at email@example.com
Edited by timo, 06 February 2008 - 01:16 PM.