Our son loves stories about space no less than other kids. To inspire his thinking, we setup his own space research project on the ceiling of his bedroom. However, the ceiling fan was the outstanding thing and we have to decorate it as satellite to put in line with other items under the roof.
Space engineers may be laughing on that project, but this is not about DIY satellite program, it’s about disguise the trivial and turn it into inspiring, brain stimulating and, actually, funny interior design stuff.
Here is illustrated story :
Here is the “green project” of modifying of telescopic table lamp from 25 watts halogen to the 1.2 watts LED cluster. Slightly less brightness, but tremendous reducing of electricity consumption.
IKEA table lamp LED upgrade
As GPS is a perfect tool to track your very own location, it’s also very interesting to know who else is sailing in neighborhood around you. With not really complicated setup it’s possible – here comes AIS (automatic identification system), that is based on idea to transmit the identity information about ship on radio. The similar system to that aviation industry uses long time since 80-s, also became standard in marine navigation.
Basically, the signal is transmitted by radio in digital format on frequencies 161.975 and 162.025 MHz (primary and secondary, marine VHF band). It looks like short messages, repeating few times per minute with identification information that provides the ship’s position, heading, speed and MMSI (the unique maritime identification number). Besides, it also contains :
- Navigation status, e.g. ‘at anchor’ or ‘under way’
- Ground speed, from 0 to 102 kts in steps of 0,1 kt
- Rate of turn, 0 to 720 degrees per minute
- Position
- Time stamp
- Callsign
- Ship’s name
- Type of ship or cargo
- Dimensions of the ship
- Draught, 0.1 to 25.5 m
- Destination
- Estimated time of arrival (ETA) at destination (at captain’s discretion)
Apparently, the first component will be a radio or scanner working on VHF band and capable to receive signal at at least one frequency, 161.950 MHz. Be advised that your receiver should not be scanning when you want to receive AIS, since it would miss AIS transmissions (hence ships) while scanning other frequencies. So, if you use a marine VHF, it should be on channel 87 or 88 constantly. Since it can’t be used for normal traffic while monitoring AIS, it is advisable to use a cheap scanner or a second marine VHF for AIS. Further to that, not all marine VHF equipment is suited to receive AIS, they need to be capable to be modified to provide discriminator output.
In our case it was a basic Uniden Bearcat 350A scanner with small modification that is vital for obtaining proper signal according to reference from very good AIS-dedicated website. The discriminator output is actually pin #10 of FM integral circuit of the scanner, in this case NJM3359 (or MC3359). If you have equipment already, please check what IC it has and if it is capable to be modified, at mentioned website, they have good cross-reference pages for that.
Modification is pretty simple and consists from connecting back 3.5 mm audio plug to the pin #10 of IC through the 10 kOm resistor to prevent discriminator output from short (red wire in the center). This will require some accurate soldering and mechanical skills, but no advanced than average. Some people don’t bother to install additional (like in this case) audio receptacle and just use the headset output, but you should realize, that discriminator is not amplified and has no control by volume knob. There are also modifications of direct connecting of piece of audio cable with jack on other end, using any appropriate hole to produce it outside of receiver.
Next step is to have audio cable connected to microphone/line-in input of audio card at your computer (we use ordinary Dell laptop and microphone input) and run the software that recognizes and decodes AIS messaging into user-friendly shape. As this was just a pilot project for proof of concept and not permanent installation for practical use, we use the trial version of ShipPlotter that is probably the best and simplest if you would not intend to invest piles of money in that.
Surprisingly, the ShipPlotter has done job very good, as you can see on screenshots:
There only one ship indicated, particularly the one we were on-board and no other in vicinity. However, during the voyage we have seen a handful of them, sometimes more that ten (in port). Of sisterhood of cruise ships, there were messages from “Westerdam” of Holland America Lines (14 knots, underway) and from “Costa Fortuna”, that was moored. Some ships were not sending names and call signs, the information was limited to MMSI with two-letter index in round brackets (like (it), (uk) or (us) – country code ?). But anyway, all of them were on the map and gave a good picture what was going on around.
The map view is most visually pleasant, but it requires the raster chart to plot ships on it. And this is not the problem, there is a perfect, free (sic!), on-line map generator for any region, that works out calibrated charts specifically for ShipPlotter. You need just to set few parameters along with the region and have your charts downloaded to accessable directory. The only manual operation is to load the chart into ShipPlotter for apropriate area, otherwise the program will plot the ship position at the middle of nowhere.
The last but not least note – the radio reception quality is critical. For this project, we have no permission to rig the balcony of cruise ship in the way to compete with pilot bridge. So, the indoor VHF antenna, “rabbit ears” with amplifier, was used with not bad results. Practically, the good antenna is a main factor, that affects the area of AIS “vicinity” for the ships be visible. So, have a good antenna rig and happy shipspotting!
Part 1 – GPS
