DRB 32
DRM Reception
+++
The following screenshots shows the DRM reception the Deutsche Welle transmitter Wertachtal at 3.995MHz running the DREAM software in waterfall spectrum mode.
The signal is usally very strong during the evening hours and well-suited for receiving experiments.
The DRM spectrum is symmetric around the 12KHz IF center frequency and occupies in contrary to analogue modulation modes always the same bandwidth.Although the Side-to-Noise ratio (SNR) is higher than 23dB there is no audio decoding possible.
The reason for this behaviour is a slowly drifting interference carrier signal which is visible at the left side of the DRM spectrum.
Some minutes later the situation has changed. The interference signal has now drifted outside of the DRM spectrum:
Distortion-free DRM reception is now possible, the SNR has simultanoiusly rised up to 28dB.
Finally some technical hints:
Distortion-free DRM reception needs a SNR higher than 13dB.
DRM reception is distorted in presence of an equal or stronger interfering signal within the DRM spectrum.
Strong fading which is recognizable as unregular wave patterns inside the DRM spectrum does not affect reception due to the robustness of the DRM coding technology.
Because the second IF value is 12KHz, the input spectrum of the DRM signal is symmectrical around the 12KHz marking. In case of DRM reception the DREAM software tunes automatically to the center frequency of the DRM signal.
Every signal tuned by the DiRaBox Control Panel software is displayed at the 12KHz marking position. In case of analogue reception the cursor has to be moved to the 12KHz position.
Due to the 15KHz IF bandwidth the passband range is +/- 7.5KHz around the 12KHz center frequency.
