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1 INTRODUCTION

Throughout the history of humanity, technology has

played an essential role in the development of society,

since largely progress is based on the invention of

procedures that solve more or less complex problems

for their practical implementation to everyday reality.

recent years has seen how many of its electronic

navigation and communications equipment have

gone from working as independent units to doing it

together, that is, to send their own information to

some and to receive from others, so that all share

useful data by improving the electronic navigation

and communications system.

This innovation project aims to make visible to the

radio-engineering learner the internal

communications that take place in a continuous way

on a wheelhouse between the different equipment

in a particular way, making them partners of their

own formation.

There is a practice of receiving the 87B and 88B

channels [9] of the Maritime Mobile Service VHF band

that have been assigned to the automatic

identification system or AIS[7], to subsequently

extract the information contained therein in

NMEA[13,14,14] format and its subsequent use in a

ECDIS[6] or information and visualization of ENC. In

addition, the same practice allows the creation of

ABSTRACT: This paper provides a demonstrative method between theoretical and practical concept for

understanding NMEA lines. This research arises from a teaching innovation project called "NMEA Protocol:

from theory to practice in internal communications" whose objective is to analyze and give visibility to radio

engineering students, in a practical, simple and real way, complex concepts present in internal communications

on board. These allow the transmission; reception and processing of information shared by the radio and

navigation teams of a wheelhouse. The challenge will be met using easily accessible electronic devices both for

their low cost and for their availability on the market. The results indicate that it is possible to demonstrate to

the student complex theoretical concepts explained in class, in part has aroused the interest of them to innovate

and experiment on their own and in a particular way, making them partners of their own formation.

During the presentation of the practice, it is

Obtaining the valid information intended to be

Once the audio signal is obtained, it is necessary to

All the information obtained in real time is now

To be able to share internally all the information

previously received in the form of NMEA sentences,

allowing several computers to access the same

information, that is, to have access to an internal

communication system that is beyond the reach and

manipulation of the equipment operator. The purpose

of using converters is to show radio-engineering

students the way digital information is shared on a

wheelhouse.

3 MATERIALS USED IN PRACTICE

3.1 Skanti radiotelephone VHF3000

assigned to the AIS system we will use a model Skanti

transceiver VHF3000, capable of receiving in the

channels of maritime communications assigned to the

maritime mobile service. It should be said that the

Ministry of Transport and Sustainable Mobility no

equipment, it is possible to locate the exact point

where it is feasible to extract the demodulated or

detected signal that interests us for practice. As a

relatively modern piece of equipment, it makes use of

integrated circuits that perform several functions in a

single element. In our case and studying the electronic

diagram, we can observe that the received radio

frequency signal is treated in its entirety in the

integrated circuit KA3361 [12], conceived almost as a

complete receiver. The datasheet of the KA3361

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allows the student to copy one of them and extract

their information on one of the many free websites

software that marine equipment manufacturers

provide, as is the case with Actisense NMEA Reader

[1]. As an example, we have chosen to copy one of the

many sentences received and after decoding it, we

observe the different parameters that make it up and

that fit the aforementioned ITU-R M.1371.

station (AIVDM). With a total number of 1 single

sentences (AIVDM, 1) transmitted to include the

information, that the sentences in question is the first

of a total of 1 (AIVDM, 1, 1) and finally that was

received in the channel AIS A (AIVDM, 1, 1, A). The

rest of the data included are much more complicated

to read in plain sight, as unlike the usual NMEA

sentences that employ ASCII[2] encoding, the ones

used in the AIS system employ a 6-bit binary

encoding due to the large data content they must

31.6999 'N and 6º 18.9700' W. etc.

3.5 Promax oscilloscope OD-606[19]

Although it is possible to obtain good results without

any electronic instrumentation, it is very convenient

to use the oscilloscope to visualize the signals shared

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digital information the use of different connection

standards,

− The tensions present in the data lines of each of

they engage in the world of repairs and maintenance.

In the course of the practice, talker and listener

were first connected by parallel cables independent of

type 24AWG[4] and the presence of a small

interference signal at both high and low levels of the

NMEA signal was clearly observed by intentionally

turning on and off a second portable VHF marine

receiver.

Only 1 pair was used in the connection, and the

same signal could be clearly observed without

appreciable interference, even repeating the process of

turning the second receiver on and off as in the

previous case.

During the development of the practice was also

proceeded to visualize the same NMEA information

at the output of a port RS232 that is, using another

standard. This second observation in the oscilloscope

helps to understand the pupil that even existing the

same information in a port RS232, this one presents

comprising the incompatibility between them.

This way helps to understanding the concepts,

graphs and values explained in classes in a very

theoretical way and that sometimes lead to be

ECDIS system, where we can see in real time the fleet

that sails near our coast, it is undoubtedly the most

eye-catching thing in practice. Although finally the

students will be shown that they can obtain the same

final result without needing several of the elements

used in the laboratory, in order to awaken their

interest in self-learning as they can carry it out alone

and at home as curiosity.

First, in the laboratory we will use a VHF

first PC in audio form.

This first PC will act as a talker, once it treats the

The second USB converter to RS422/RS485

As soon as we install ShipPlotter software on the

At this point only the VHF needs to be turned on

We will connect the dedicated audio output from

Jack 3.5 mono connector, to the microphone input of

the PC1 or talker.

We will patiently wait a few seconds. If near our

receiver there are AIS transmissions, we will be able

to observe how information about the static data

appears on the ENC of the PC2 or listener, dynamic

and crossing of the ships around us, of the stations

listener via port 2 to 4800 baud, but no longer as audio

but as signal converted to NMEA protocol.

The talker port 2 in turn connects with the listener

port 3 at the same speed of 4800 baud, because if both

ports do not work at the same speed they cannot be

"understood." The information received by this port is

interpreted as incoming information using the

protocol NMEA0183 and will be used according to the

function programmed in the listener.

We see in the image that OpenCPN also allows

time thanks to a debug window. This utility allows

extracting certain sentences, or all of them, for further

study and understanding and even for archiving in a

file that may later be used for other purposes.

Information sentence can be represented in

different ways, one of them being a radar screen

simulation, but always remembering that it is

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of operation of a real radar is completely different.