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User Manual WS 19 / March 2011 © ASL Intercom BV
.
8.0
FREQUENCY BAND & ANTENNA’S
8.1
Frequencies
ASL‟s wireless intercom uses the 2.4 GHz band,
which is freely available for WLAN (Wireless Local
Area Networks).
The ASL system divides the available bandwidth
into 16 overlapping sections, 8 of them being used
as upload frequency (from the beltpack to the
base station) and the other 8 being used as
download frequency (from the base station to the
beltpack).
With the channel select switches on both base
stations and wireless beltpacks one actually
selects an upload/download pair,
called a TX/RX
channel
.
Each TX/RX channel serves one dedicated
wireless connection between base stations and
wireless beltpacks (in fact between the TX/RX
modules in those units). It is possible to have
several WS 19 beltpacks on the same TX/RX
channel, see section 10.2
“Half Duplex”
.
When using the ASL wireless system, the
following should be taken into account:
o
The 2,4 GHz frequency is known to have
difficulty in penetrating concrete walls,
steel walls and other obstructions. Behind
obstructions like these an “HF shadow”
may occur where no communication is
possible.
o
The antenna‟s of a base station should
have as much as possible a “line of sight”
to the antenna‟s of the beltpack(s). All
objects within that path make the
connection less reliable.
Due to reflections of the HF signal, one
might experience a dropout on a specific
spot in a building; moving a beltpack only a
few inches can be enough to solve the
problem.
o
Because of the use of the WLAN
frequenc
ies, ASL‟s wireless units might
experience interference from units like
mobile telephones with bluetooth and
computers with bluetooth or WLAN cards.
Try to change TX/RX channels if you
experience problems with these.
8.2
Antenna Wiring (Base Stations)
If the antennas of a base station are not supposed
to be directly connected to its front panel, a cable
between base station and antenna is needed
(base stations are equipped with SMA connectors
- female at the base station and male at the
antenna).
The 2.4GHz frequency experiences a big loss in
any cable, e.g. a RG58 cable has a loss of 1 dB
per meter. So make sure that your cable (50
ohms) is suited for 2.4 GHz and that the cable is
as short as possible. Make the cables in lengths of
a multiple of 12, e.g. lengths of 24cm, 48cm,
120cm, 240cm etc.
9.0
SETTING UP CONNECTIONS
9.1.
ASL WIRELESS AS A STAND ALONE SYSTEM
9.1.1 Base Station Settings
a. Give each TX/RX module in the base
station its own TX/RX channel by rotating
the „Channel select‟ switch.
Try to avoid TX/RX channels to be
physically next to each other, e.g. when
two WS-
400‟s
are in your wireless system,
try to set them in this order: TX/RX
channels 2, 4, 6, 8, 1, 3, 5, 7. If one uses a
WS-200 with only two beltpacks, use
TX/RX channels 1 and 6
b. Make sure the interface mode switch at the
rear of the base station is set
to “
PARTY
LINE
”.
The internal party line is now linking
the on board TX/RX modules to each
other.
c. Turn down the side tone trimmers at the
TX/RX modules (counter clockwise)
