Wavecom W61PC V7.5.0 - Manual (Page 193)

WAVECOM Decoder W61PC/LAN Manual V7.5 Transmission Modes  183
Parameter Value
Center frequency 1500 Hz
Receiver settings FM BW = 12 kHz
Input format(s) AF, IF
NMT-450 mobile station signals can be found from 453 MHz to 457.5 MHz, base station signals from 463
MHz to 467.5 MHz. The frequency range is divided into 180 channels of 25 kHz each (channel 1 -180).
In areas with a lot of mobile subscribers, an extended band from 452.5 MHz - 452.975 MHz (mobile) and
462.5 MHz - 462.975 MHz (base) may be used as an option. The offset between mobile and base frequen-
cy is always 10 MHz.
Control messages (signals) containing system wide information, assignment, status and dialed number are
exchanged between the mobile station and the base station.
All signals are transmitted at 1200 Bd FFSK with a center frequency of 1.5 kHz and a shift of 600 Hz.
An encoded NMT-450 frame has a length of 166 bits. Every frame contains 15 bits bit sync sequence fol-
lowed by an 11 bits frame sync sequence. The last 140 bits contains the encoded message. In order to
combat errors on the radio path, due fading and interference, an error-correcting code is used.
Today, NMT-450 is used in Sweden and a modified NMT-450 in Poland and Eastern Europe. More infor-
mation can be found in the NMT DOC 450-1 / 450-3 specifications.
NOAA-GEOSAT
The NOAA-GEOSAT software has been specifically tailored to the transmissions of meteorological satellites.
Transmissions are always at 120 rpm using an IOC of 576. In contrast to short-wave stations which use
frequency modulation, satellite weather images are transmitted using amplitude modulation.
Parameter Value
Frequency range VHF/UHF
Operation modes Broadcast
Modulation FM, SUB AM
Center frequency 1800 Hz
Speed 120 RPM, IOC=576
Receiver settings FM, BW = 40 kHz
Input format(s) AF, IF
The software is started in free-run mode by enabling the mode. Because this mode has no synchronization
sequence the correct display of the image is controlled by using the Phase function in the Options menu.
The special items AM-Gain and AM-Offset are placed in the Demodulator menu. Centering of the signal
deviations on the bar graph is controlled by adjusting AM-Offset. In addition maximum deviation is re-
quired on the bar graph. This is done by adjusting AM-Gain. It should be noted that these two adjust-
ments are influenced by each other.
The orbiting satellites may be received with an active antenna and a high quality VHF-UHF receiver. An
optimal receiving station allows reception for approximately 20 minutes before the satellite has moved be-
low the horizon. The AF output of the receiver may be fed directly into the decoder, which converts it into
a weather image viewing station providing excellent image quality.
Polarization problems occur with orbiting satellites resulting in reception gaps of up to 2 minutes. A special
antenna may alleviate this problem.
Due to the Doppler effect the frequency of the received signal may change as much as 1000 Hz during the
reception period. The receiver should therefore have a built-in automatic frequency control (AFC) capabil-
ity.