Two transmitters - one frequency! | DW Digital Radio DRM | DW | 19.05.2005
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DW Digital Radio DRM

Two transmitters - one frequency!

Revolution on the air: For the first time ever, a digital DW programme is transmitted on one and the same frequency by two different transmitters, resulting in an improved reception quality.

So-called single frequency networks (SNF) offer many advantages as well as challenges. In the times of analog transmissions only, these could not be met by shortwave technology. With the new digital technology, however, things are different. For the first time ever in the world of shortwave, DW is testing a digital single frequency network under realistic operational conditions.

Aim: a reliable reception

The main objective is to cover a defined target area with a consistently stable signal strength, which is the prerequisite for an interruption-free reception. Whereas with analog shortwave transmissions the broadcast disappears in the noise accompanying a weak signal, the digital receiver remains silent, the broadcast is being interrupted.

Single Frequency Network

Map of Deutsche Welle's Single Frequency Network

DW's digital single frequency network with the transmitter stations Sines in the south of Portugal, Wertachtal (centre of the picture) and the synchronization point Bonn, marked with a cross. Within the area circled in red an improvement of the reception quality is expected to be obtained.

The number of such interruptions within a broadcast can be decreased considerably by transmitting a synchronized digital signal on one and the same frequency from two different locations. The DRM receiver is tuned to that one frequency and the listener can - ideally -receive the broadcast interruption-free. For the receiver itself, it does not matter from which location the signal is being received.

Synchronized to the millisecond

In an ideal case, at least one signal is strong enough to make a transmission possible, so that if one signal fails because of screening or bad propagation conditions, the other signal fills the gap. For the listener, this means that digital shortwave reception offers an undisturbed listening pleasure.

The main task for the engineers is to synchronize the signals to the millisecond. As both transmitters used, Wertachtal and Sines, are at different distances from the target area, the corresponding signals take different times to span the distance. The signal originating in Wertachtal is sent on its ways with a 4 ms delay and is thus optimized for the synchronous reception at the broadcasting centre in Bonn. The maximum run-time tolerance of 5.3 ms of the receivers, however, make an improvement of the reception quality throughout the entire target area possible.

Test transmissions from Sines and Wertachtal

For the time being, Deutsche Welle is testing its single frequency network with the transmitters in Sines, Portugal, and Wertachtal on Mondays, Wednesdays and Fridays.
Sines only is used on Tuesdays and Thursdays, and Wertachtal only is used on Saturdays and Sundays. The frequency used is 7265 kHz, the time of transmission 07.05-08.55 UTC.

Thus, a test of the SNF is possible on Mondays, Wednesdays and Fridays, whereas reference measurements from Sines can be taken on Tuesdays and Thursdays and from Wertachtal on Saturdays and Sundays. As always, observations and reports (with or without logfiles) are welcome at the address Translation: Silke Broeker

  • Date 19.05.2005
  • Author dh
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  • Date 19.05.2005
  • Author dh
  • Print Print this page
  • Permalink