In the Modulation pull-down list the user may set the demodulator of a mode decoder.

Most HF, VHF or UHF modes use a pre-selected demodulator mode for optimum performance, but sometimes different demodulators may be chosen.

AM

Satellite weather charts are transmitted using AM. This demodulator uses the quadrature I/Q demodulation method.

The level displayed by the level indicator corresponds to the AM modulation depth of the signal.

BPSK

BPSK shifts the carrier phase ±180 degrees. For carrier recovery a Costas loop is used - this is a PLL with a special phase comparator, which removes the payload data from the PLL loop. The input signal is then down-converted to base band by mixing the carrier in a complex mixer, and the resulting signal is the data signal.

BPSK is almost exclusively used for satellite data links.

CW

The CW demodulator utilizes a steep, adaptive band pass filter and automatic amplitude control. The AGC attack time may be adjusted according to the propagation conditions. The filter response may be set to Slow, Normal or Fast. This demodulator produces high quality CW decoding. It is important to select the appropriate receiver AGC response (normal or slow).

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 resultant signal is used for the frequency conversion. This method is characterized by a linear relationship between 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 following 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 (Hilbert). 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. Depending 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 extremely 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 signal 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 symbol duration the quadrature part is switched. The advantage of this process is a smaller amplitude variation.

OQPSK is used almost exclusively for satellite data links.

QPSK

Carrier recovery is mandatory to demodulate QPSK. As QPSK has phase shifts at ±90 and ±180 degrees, the signal 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.

QPSK is almost exclusively used for satellite data links.

SUBTONE

The same as DSP, but the parameters are optimized for low frequencies.