Datawell Waverider Buoys
https://www.datawell.nl/Portals/0/Documents/Brochures/datawell_brochure_dwr-mk3_b-09-09.pdfhttps://www.datawell.nl/Portals/0/Documents/Brochures/datawell_brochure_dwr-g_b-07-11.pdfhttps://www.datawell.nl/Portals/0/Documents/Brochures/datawell_brochure_dwr-g4_b-06-10.pdfhttps://www.datawell.nl/Portals/0/Documents/Brochures/datawell_brochure_wr-sg_b-33-07.pdfhttps://www.datawell.nl/Portals/0/Documents/Brochures/datawell_brochure_dwr4_acm_b-38-07.pdfhttps://www.datawell.nl/Portals/0/Documents/Brochures/datawell_brochure_dwr-mk3_b-09-09.pdfI believe that's what I heard yesterday on 27.755 USB 27755 27.755 MHz USB - center frequency seemed closer to 27.756 MHz or 27.757 MHz.
I know the Datawell HF Link is 25.5 MHz to 35.5 MHz (standard coverage) or 35.5 MHz to 45 MHz band (special request). The 25.500 MHz to 35.500 MHz band is almost certainly the more commonly used band. 25.5 MHz to 28 MHz and 29.7 MHz to 30 MHz are probably very heavily used for these types of transmissions. Here's another good information page on it:
https://www.sigidwiki.com/wiki/Datawell_Buoy_HF_LinkThe Datawell documentation indicates a 50 km range over sea using the "HF data link" 25.5-35.5 MHz. According to the documentation for the RX-D2 data receiver for the Datawell Buoys - the frequency for the HF link is crystal controlled and the crystal is included installed from the factory - FSK data link 81.92 bits/second BCH (63, 51) error correcting code.
Receiver bandwidth: 1.2 kHz IF bandwidth, 200 Hz detector bandwidth.
Transmitter technical specifications:
The buoy transmitter converts the combined digital data stream which contains the wave height
data, wave spectra, wave direction, seawater temperature etcetera into a high frequency (H.F.)
signal.
Technical details:
The HF output signal of the transmitter is FSK modulated with a rate of 81.92 bits per second in
a bandwidth of 200 Hz and a radiated power of
75 mW (19 dBm). The transmit frequency is
crystal controlled and between 25,5 and 35,5 MHz.
Buoy transmit antenna
The transmit antenna is the interface between the buoy transmitter and the physical channel,
namely the atmosphere.
Technical details:
A vertically polarized quarter wavelength whip with a gain of 2 dBi is used as a transmitting
antenna for the Waverider- and Directional Waverider buoys, except for the DWR-G 0.4m.
The seawater around the buoy (or an other artificial ground plane) is an important part of the
antennas counterpoise and is therefore absolutely necessary for the buoy’s transmission system
in order to radiate its power efficiently. In other words, a buoy without a high conductance
groundplane such as normal soil2 will have a severely limited range.
The transmit antenna is of an omni directional type because the rotation of the buoy is
undetermined with respect to the receiving station.
"The RX-D2 is delivered with a factory-installed receiver crystal. This receiver crystal can be
exchanged to allow reception of other frequencies within the specified frequency range (see
chapter 6).
When the frequency of the receiver needs to be changed, the recommended procedure is to send
the RX-D2 back to Datawell for exchanging of the crystal and subsequent realignment of the
receiver. Please contact Datawell sales for more information."https://www.datawell.nl/Portals/0/Documents/Manuals/datawell_manual_rx-d2_2015-10-14.pdfWith these band openings...I bet we'll be seeing a lot more of these types of data link transmissions. There are a lot of different "Class C" data link, telecommand, telemetry, paging, pager and similar systems all over the 11 meter region.
27.255 MHz is the big one in the USA. There are a dozen or so known active frequencies in the 26 MHz region used in Europe, including 26.945 MHz, 26.950 MHz, 26.955 MHz, 26.960 MHz (plus 26.995 MHz, 27.045 MHz, 27.095 MHz, 27.145 MHz, 27.195 MHz and 27.255 MHz).
26.150 MHz, 26.200 MHz, 26.250 MHz, 26.650 MHz, 26.665 MHz, 26.700 MHz (offset frequencies from 26.7 MHz including 26.695 MHz are popular), 26.850 MHz, 26.935 MHz and several other frequencies are used for on-site paging, including hospital paging services...much like 27.255 MHz is used in the USA. POCSAG paging signals have been monitored all over the 11 meter band, including on weird offset frequencies like 27.007 MHz, 27.003 MHz, 27.000 MHz, etc.
I have personally monitored POCSAG paging signals on 27.255 MHz in the USA.
Here is a page with information on one of the telemetry systems that use 27.255 MHz with 10 watt transmitters:
https://www.nortekcontrol.com/products/radio-controls/xt-4-4-channel-stationary-mid-range-transmitter/https://www.nortekcontrol.com/wp-content/uploads/XT-4.pdfI know that there are other devices manufactured by the same company that use 26.995 MHz instead of 27.255.
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