Diversity Reception
In radio
systems it is not necessary to have a direct
visual connection between the master station and
the moving substation because the radio signal
transmits by reflecting from buildings and
terrain e.g. such as hills. The fading occurs
when the radio signals reflect from several
objects to the antenna of the receiver. The
propagation speed of the radio signals is at the
speed of light so the signals reflecting from
different objects arrive into the receiver at
different times. The signals at the receiving
antenna are in different phases so in the worst
case two equally strong signals being in
opposite phases cancel each other out and thus
will cause the fading. The dips of the signal
appear with half wave intervals. In connections,
which are only based on reflections, the
reliability of the signal receiving is depending
on the position of the receiving antenna even
ones fairly close to the base station.
By setting the
two antennas of the diversity receiver at least
¾ x wavelength apart from each other the message
can always be received by one of the receivers
if not both. When installing the antennas in
this way they are rarely at the same time in the
fading dips.
Dual Band Version
The SATELLINE-3AS(d) Epic modem is available
also as a "Dual Band" version. The transceiver
of the radio modem offers as an option two 2 MHz
frequency bands, tuned at the factory with a
maximum separation of 15 MHz between the highest
and the lowest frequency. The radio modem can be
reprogrammed to operate at any channel within
those two bands.
Specifications:
|
Transceiver |
|
Frequency range |
370 - 470 MHz |
|
Channel spacing |
12.5 / 25 kHz |
|
Communication mode |
Half-duplex |
|
Transmitter |
|
Carrier power |
10 mW ... 1 W / 50 ohm |
|
Receiver |
|
Sensitivity |
-116 ... -110 dBm (BER < 10 E-3) |
|
Diversity |
> 60 dB /> 70 dB |
|
Data Modem |
|
Interface |
RS-232, RS-422 or RS-485 |
|
Interface connector |
D 15, female |
|
Data speed of RS interface |
1200 - 38400 bps |
|
Data speed of radio interface |
19200 bps (25 kHz channel) 9600 bps (12.5 /
20 kHz channel) |
|
Data formats |
Asynchronous data |
|
General |
|
Operating voltage |
+8 ... + 30 Vdc |
|
Power consumption |
1.8 VA typical (receive) 6.0 VA typical
(transmit) 0.05 VA typical (when DTR is "0") |
|
Temperature range |
Operating: -25 C ...+55 C (tests acc. to
ETSI standards), -40 C ...+75 C (absolute minimum / maximum). Storage:
-40 C … +85 C |
|
Antenna connector |
TNC, 50 ohm, female |
|
Construction |
Aluminum enclosure |
|
Size H * W * D |
137 * 67 * 29 mm |
|
Weight |
250 g |