Start making noise

May 2, 2006.

Start making noise (OP-170-E option)

A traditional set-up for measuring DVB-T performance versus C/N typically includes a source of wideband white Gaussian noise, an RF power meter plus selective channel filter or a spectrum analyser, and a varying number of high-precision variable attenuators and directional couplers. The C/N generation function available in the digital DVB-T modulator MO-170 makes this kit no longer required and allows a much simpler configuration.

In the MO-170, white Gaussian noise with twice the bandwidth of the DVB-T signal is digitally added to the COFDM signal. C/Ns between 3 and 40 dB in steps of 0.1dB can be selected. In addition, the RF signal level (COFDM and noise combined) can be further attenuated from 0 to 60 dB in 1 dB steps. This provides the means to either keep the signal power constant whilst varying the C/N (e.g. to plot the BER vs. C/N of a demodulator), or to keep the C/N constant whilst varying the signal power (e.g. to find the sensitivity of a receiver).

The DVB-T signal may be switched off while the noise is still on, and vice versa. This way, noise and signal average powers can be measured externally using the appropriate equipment so as to verify the selected C/N reading. The fact that both noise and signal are digitally synthesised has the added benefit of generating C/Ns with a precision that is difficult to achieve in a traditional assorted test set-up.

Spectral snapshot of a C/N of 20 dB generated with the MO-170

Digital DVB-T modulator MO-170 screen
Spectral snapshot of a C/N of 20 dB generated with the MO-170