Wavecom W-SPECTRA (Automatic Monitoring System) V1.1.0 - Manual (Page 58)

48

Parameters and Options WAVECOM Monitoring System W-SPECTRA, W-SPEED Manual V1.1.0
DSP
The DSP mode utilizes an I/Q demodulator (Hilbert transformation). The received signal is split into an in-
phase component and a quadrature component. Next, amplitude normalization takes place and the result-
ant signal is used for the frequency conversion. This method is characterized by a linear relationship be-
tween the received frequency and the output voltage of the demodulator.
The DSP demodulator has a good signal-to-noise ratio and yields very good results under most conditions.
DPSK
In differential PSK the absolute carrier phase cannot be used for data recovery as is the case with BPSK
and QPSK. To decode multiphase DPSK (up to 16DPSK) the input signal is mixed with a complex, phase
regulated reference signal. The resulting data reduced signal is then filtered in a low pass filter. The fol-
lowing phase comparator calculates the phase difference between the signal from the integrator and the
delayed signal.
A variant of DPSK is used almost exclusively when phase modulation is employed on short wave data
links.
DBPSK
Similar to DPSK, but has two phase shifts at ± 180 degrees.
DQPSK
Similar to DPSK, but has four phase shifts at ± 90 and ± 180 degrees.
DTMF
This demodulator handles multi-frequency signals. Filters are switched in on the various frequencies of the
signal and the amplitude is then calculated for each frequency. Next the amplitudes are evaluated. Two
simultaneous tones are demodulated. The SNR is the same as for the mark-space demodulator.
DXPSK
Adaptive DPSK demodulator for PACTOR-II. This demodulator will automatically adapt itself to DBPSK,
DQPSK, D8PSK or D16PSK.
D8PSK
Similar to DPSK, but has eight phase shifts at ±45, ±90, ±135 and ± 180 degrees.
D16PSK
Similar to DPSK, but has sixteen phase shifts at ±22.5, ±45, ±67.5, ±90, ±112.5, ±135, ±157.5 and
±180 degrees.
FFSK and GFSK
Depending on the mode, the FFSK (Fast Frequency Shift Keying) and GFSK (Gaussian Frequency Shift
Keying) demodulator is automatically selected. Basically this demodulator utilizes the I/Q principle (Hil-
bert). However, filters are adjusted to accommodate the special demands of these modes.
MFSK
This demodulator handles multi-frequency signals. Filters are switched in on the various frequencies of the
signal and the amplitude is then calculated for each frequency. Next the amplitudes are evaluated. De-
pending on the number of tones used, the filters are configured as phase linear FIR filters or as IIR filters.
The SNR is the same as for the mark-space demodulator. Simultaneous multi-tone decoding (e.g., DTMF)
is not possible with this demodulator.
MS (Mark-Space)
The mark-space demodulator processes the two keying frequencies of a FSK signal. These are fed to two
phase linear FIR filters and the amplitude is then calculated. The mark-space demodulator exhibits an ex-
tremely good noise distance and should be used for all FSK modes utilizing a speed of less than 300 Baud.
OQPSK
Carrier recovery is mandatory to demodulate OQPSK. As OQPSK has phase shifts at ±90 degrees, the sig-
nal must be squared two times to produce a carrier at four times the original frequency. A PLL recovers
the carrier in frequency and phase with ambiguities at ±90 and ±180 degrees. A complex mixer down
converts the signal to base band and the resulting signal is the data signal. In contrast to QPSK, OQPSK
has only phase steps of ±90 degrees in one step. First the in-phase part is switched, then after half a