Specifications

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5.16 HF communication
The default way of communicating the wave data to the shore is through HF communication.
Each buoy transmits at its own frequency, thus allowing several wave measurement buoys in the
same area at sea. A large set of frequencies in the range 27-40 MHz is available. The
transmitting range extends to beyond line-of-sight and amounts to some 50 Km. Data are
transmitted continuously by Frequency Shift Keying (FSK) at a rate of 81.92 baud. Please refer
to the data format section 5.7 for the data structure. The most important transmitter
specifications are summarized in Table 5.16.1.
As indicated in the LED flasher section, the HF whip antenna should be placed on the
option port labelled HF. Reassure yourself that the rubber sealing ring is in place and that insert
and port are clean and dry before doing so. Fasten the six hexagon socket screw-bolts.
Obviously for checking the HF output power the whip antenna must be in place. To merely
receive the HF data signal on your buoy receiver in close proximity of the buoy, for example
while servicing or testing the buoy in your laboratory, the whip antenna may be removed for
convenience.
Table 5.16.1. Transmitter specifications.
Parameter Value
Radiated output power 75 mW
Frequency range 27 - 40 MHz
Frequency deviation ±80 Hz
Transmit range 50 Km (over sea water)
Link baud rate 81.92 baud
Modulation FSK
Error correction BCH(63, 51)
To limit wind-sail a short and slender HF whip antenna is used on the DWR-G 0.4 m.
The smaller length requires a small matching network in the electronics unit, see subsection
5.11.3. Transmission range of the DWR-G 0.4 m is 10 Km with a handheld receiving antenna
and 25 Km with a properly grounded receiving antenna. For transport the stainless steel whip
may be unscrewed.
5.16.1 Transmitter frequencies
Within the range of 27-40 MHz the user may freely choose the preferred transmitter frequency.
Given a certain frequency, the transmitter is fine-tuned by Datawell at the factory for optimum
performance. Should you wish to change the frequency, please contact Datawell sales first. It
depends on the type of transmitter installed if the frequency can be changed by the user or if the
electronics unit must be send back to Datawell for re-tuning.
The installed transmitter type can be identified by the serial-number and type of the
buoy or alternatively by the 'P' number on the transmitter board (see the section "Electronics
unit" for more details).
5.16.2 HF antenna
The majority of buoys are equipped with data transmission through HF radio link. The HF whip
antenna incorporates a LED flasher to mark out the buoys presence and location. The antenna is
mounted on a spring. On the one hand, to avoid breaking of the antenna, the rigid spring will
subdue in a collision. On the other hand, it will not bend under wind force in order to maintain
the data link.
This option fills the HF-port on the hatch. A drawing is shown in Figure 5.16.1.