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I am working in a project with a fleet of several fishing boats. I am measuring their locations with a GPS module and some other data with a set of sensors and a micro-controller. I would like to send this data in real-time over a radio frequency link to mainland.

  • Ships could be located far away, around 100-400km.
  • There is no GSM coverage.
  • Satellite link should not be used.

I have evaluated using Xbee modules, however they are limited to line of sight and power limitations.

I have read that working in the MF/HF band, long ranges may be reached, specially using skywave propagation, in which the wave reflects with ionosphere. However I can not find commercial OEM modules on this frequencies to integrate with a micro-controller.

Update:

  • Max distance for a ship from the coast is 80 nautical miles (148 km).

I was reading about sending digital data through VHF radios using APRS. According to Wikipedia:

Automatic Packet Reporting System (APRS) is an amateur radio-based system for real time digital communications of information of immediate value in the local area. Data can include GPS coordinates, weather station telemetry, text messages, announcements, queries, and other telemetry.

APRS uses 2m amateur band (142-148 MHz), which means that commercial amateur radios can be used after converting digital signals to audio tones by a Terminal Node Controller (TNC).

Do you think these distances can be achieved using APRS with handheld VHF radios?.

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  • \$\begingroup\$ Have you met LoRa? \$\endgroup\$ – brhans Apr 4 '18 at 19:38
  • \$\begingroup\$ "LoRa enables very-long-range transmissions (more than 10 km in rural areas)" (Wikipedia) ... some way short of 400km. \$\endgroup\$ – Brian Drummond Apr 4 '18 at 19:42
  • \$\begingroup\$ Yes, I have seen some Lora modules. They have similar range to Xbee modules, and because they operate in the ISM band LOS is required. I have read about long distance transmission using LoRa in Air Balloons (there is no obstruction because of earth curvature). \$\endgroup\$ – DanielG Apr 4 '18 at 19:47
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    \$\begingroup\$ Consider using AIS (Automatic Identification System) - your vessels may already have AIS transponders, and there are satellites monitoring AIS transmissions over the oceans. See if you can find your vessels on marinetraffic.com or other AIS display sites. \$\endgroup\$ – Peter Bennett Apr 4 '18 at 19:59
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    \$\begingroup\$ VHF might work at 80 nautical miles, if the shore station is on a fairly high mountain, but you would need a fixed-mount radio and good antenna on the vessels. You would also need to obtain a license and appropriate frequency allocation for this. \$\endgroup\$ – Peter Bennett Apr 6 '18 at 20:04
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Satellite is the solution.

HF telemetry is incredibly specialised, requires licenses, and there are not "modules" in the sense you think of. (little pcbs that are cheap)

There are many systems for data over HF radio, both commercial and amateur - go looking in the Ham radio world for Digital Modes where there is much info. Data rates are low.

However, even though your fishing boats may have HF marine radios, they are probably not licensed to use marine channels for telemetry, and would need licensed channels.

You might find it interesting to look at the WSPR low power HF beacon map during the day, to see how the propagation patterns shift around the world.

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You might also want to take a look at Meteor burst communications, bouncing VHF off ionized meteor trails. It's apparently pretty reliable.

https://en.wikipedia.org/wiki/Meteor_burst_communications

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What is possible here? Consider line-of-sight, for 10,000 bits/second datalink over 1,000 kilometer range. How much TX power, in a vertical whip antenna, must you provide? Here is (1) receiver input RF power, and (2) pathloss computation:

(1)-174dBm/rtHz Thermal Floor in receiver

4dB Noise figure and Matching losses

40dB For bandwidth needed (10,000Hz)

10dB The signal-noise-ratio (some coding)


(1)-174 + 54 = -120dBm (about 0.6 uV peakpeak)

(2)Now the path loss(assume at 60MHz):

22dB + 10 * log10( [distance/wavelength]^2 )

22dB + 10 * log10( [1,000,000 meters/5meter] ^2 )

22dB + 10*log10( 200,000^2 ) = 22dB + 10 *log10(0.04 Trillion)

22dB + 10 * (12 - 1.4) = 22 + 10*10.6 = 22 + 106 = 128dB

And we need -120dBm at receiver (assume another zero-gain whip antenna) so we add the dB -120 + 128 = + 8dBm, which is 1mW * 2 *sqrt(10) = 7milliWatts.

If there are no losses due to propagation. NASA has this situation in space. Across the ocean, you have a different situation.

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