Wavecom W40PC, Manual

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WAVECOM Decoders v6.15 W40PC, W41PC, W51PC Transmission Modes
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FAX Transmission Sequence
Carrier Modulation
On HF and VHF-UHF different carrier modulation methods are used.
The most frequently used modulation techniques are 2FSK using two frequencies, MFSK with
four or more tones and differential phase modulation methods as 2DPSK, 4DPSK, 8DPSK or
16DPSK. On satellite links phase modulation methods as BPSK or QPSK are used. The DSP
demodulator handles the demodulation of these modulation methods.
A distinction must be made between the modes in use for
HF transmissions
,
INDIRECT
FM modulation , INDIRECT AM modulation and DIRECT FM modulation . Depending
on the mode, the AF and HF inputs may be used (HF modes), or only the AF or IF input.
SSB (Single Side Band)
Most modes in the HF bands use SSB modulation with suppressed carrier keying. Decoding
can be done from the receiver AF or IF output (USB, LSB, CW or FAX demodulator).
DIRECT FM
PAGER modes and PACKET-9600 mode on VHF-UHF use DIRECT (carrier) FM
modulation. The frequency shift is in the range 3000 – 10000 Hz. Decoding is only possible
from the receiver IF output. To exploit the comprehensive analysis tools included in the
decoder (baudrate, shift measurement, FFT, waterfall etc.), amateur receivers should be
provided with an IF output.
A new generation of VHF-UHF receivers (from ICOM, AOR and others) has direct
discriminator output, which may also be used for decoding of these modulation types.
INDIRECT FM
Modes using INDIRECT modulation (sub-carrier modulation) are twice modulated.
One method is to modulate a frequency modulated carrier with FSK (Frequency Shift Keying).
For decoding, the receiver FM demodulator output is required. Examples of INDIRECT
modulation are PACKET-1200, ATIS, analog and digital tone call systems. Decoding is only
possible from the receiver AF output.
INDIRECT AM
Another method of INDIRECT modulation (sub-carrier modulation) uses AM carrier
modulation, which in turn is FSK modulated. For decoding the receiver AM demodulator
output is required. At the time of writing, ACARS is the only known mode using this
modulation method. Decoding is only possible from the receiver AF output.