12
For interference free reception it is advisable to install the Receiving antenna as far as possible
from local interference sources such as combustion engines, electric motors and fluorescent
lamps. In general a transmitting distance of 50 Km (30 n.m.) over sea water can be attained
when the receiving antenna is located at least 100 m from interference sources mentioned. If
considerable interference is present at the location where the receiving equipment has to be
installed, the antenna should be moved to a position with lower interference. Also the use of a
directional antenna (see
Appendix D
) can be considered. Transmission range of the DWR-G
0.4m is less: line of sight with a handheld receiving antenna and 25 Km with a ground plane
antenna.
Installing the antenna cable
The length of the antenna cable is not critical as long as a good quality coaxial cable is used.
The supplied RG 213 cable has an attenuation of 3.5 dB/100m allowing up to 200m of cable
lengths. However, shorter cable lengths are always preferred to improve the signal to noise
ratio. Especially in signal limited situations (where signals of buoys at the edge of the normal
range must be received) the cable should be no longer than strictly necessary. Install the coaxial
cable without stretching or bending and avoid mechanical stress. With respect to routing there
are few restrictions. Although the cable is screened and not very sensitive to surrounding
electric or magnetic fields and disturbances, try to avoid routing the cable directly along power
cabling.
Be aware of the fact that reception in most areas is limited by local noise and interference. It
pays to install the antenna in such a way that distance to local sources of noise and interference
is maximized. In these situations, it is entirely acceptable to use a longer cable in order to install
the antenna further away from a source of interference.
Using a directional antenna
In case of weak signal and/or high local noise or interference the use of a directional antenna
can be considered. The sensitivity of such an antenna is 3 dB higher in the direction of the buoy.
Interference and noise generated at the landside will be attenuated by 6 dB. The combination of
gain at the front side (thus towards the buoy) and suppression of noise from the backside of the
antenna will improve the signal to noise ratio.
Using an antenna splitter
For connecting multiple receivers to a single antenna, the Datawell Antenna Splitter can be
used. This device is optimized for the buoy reception frequencies and signal levels. With the
Datawell Antenna Splitter up to six receivers can be used with a single antenna.
3.3 Connecting the serial output to a PC
Connection of the serial output to a PC is done using a standard D-SUB RS232 cable assembly.
The receiver has a nine pin D-SUB outlet of which only pins 2 and 3 carry active signals. To
prevent crosstalk issues, pins 1,6,8 and 9 are internally terminated to signal ground by a 100Ω
resistor. Pin 5 is signal ground. Normal RS232 cable length restrictions apply. RS232 ports are
becoming scarce on PC’s, in favour of USB ports. This problem may be solved with a RS232-
USB serial adapter. However, some adapter models do not offer the same data transmission
reliability as RS232 serial connections do.
