The knowledge gained in the exam preparation hardly helps when it comes to the selection and installation of the device. The purpose of this article is to give some suggestions.
Selection of the device
First, you have to be clear about where you want to operate the device. There are some for maritime radio, for inland radio and also combi devices that may be used in both areas. The peculiarities are examined extensively in the radio certificates so that I can presuppose them here as known.
An existing approval in Germany is the next selection criterion. It is not enough that the device has a CE mark, but it must also be listed at the Federal Network Agency (BNA). This is usually the responsibility of the manufacturer or importer. An approved device receives from the BNA a 6-digit number, which must be specified in the application for approval. In most cases you get this number from the seller, if not a call to the BNA creates clarity. You have to be a little careful and pay attention to the exact type of designation. There are certain devices that have a license in the pure maritime variant as a domestic or combined device but not.
Otherwise, one can largely be guided by his taste. The regulations are so narrow that there are hardly any technical differences. Hauptauswahlkriterium is therefore where do I want to install the device and tells me the user interface. Information about it is easiest to get through the manual. So it’s a good idea to get them in advance and study them thoroughly. This is not a problem, at least in the English version you can find them all on the Internet.
In most cases, the device will be installed somewhere at the navigation station. This has the disadvantage that you can not hear the current radio traffic outside in the cockpit. This, in turn, makes sense, because in many cases the monitoring of the working channel alone provides you with the best possible information even without having to make an extra request to the control center. You do not necessarily need a permanently installed, watertight secondary speaker. I get along great with one of the amateur radio accessories, which I install if necessary flying under the sprayhood. For an additional waterproof control unit on the control column to be able to send from there, as some consider necessary, I could not inspire me either. I bought an extra handset instead. That was cheaper and in case of the case I can take it with me to the liferaft. I think this solution makes more sense. Hand-held radios are permitted in Germany only in maritime traffic and not inland.
Not the radio but the antenna determines the range. Exactly even is not the antenna but their construction height. This is because ultrashort waves (FM) propagate like optical light. That’s about as far as you can see – clear view. With the well-known formula for a fire in the Kimm, you can calculate the range quite well. Just as one already anticipates the reflection of the fire before it comes right into view or even dawns before sunrise, radio waves also go a bit beyond the optical horizon. However, you have to fight for every kilometer and drive accordingly. That is not worthwhile with the Seefunk regularly. By contrast, the optical range can already be achieved with very low transmission power. Investing in expensive, Low-loss coaxial cables and complex antennas can, therefore, be saved. The three most important rules for the antenna onboard are 1. high; 2nd high; 3rd high. The VHF marine antenna belongs to the mast top. Everything else is not that crucial.
It is similar to the antenna gain, which is discussed again and again. An antenna can not conjure up and profit, on the one hand, means a loss on the other. Antenna gain is nothing but a stronger bundling of radiation in a particular direction. But that does not bring anything, even if less focused radiation reaches to the horizon. On the contrary, from the picture on the left, it becomes clear that the bundled radiation of an antenna with a profit is counterproductive when the ship is crowding. That is another reason why an antenna with a length of about 1 m (λ / 2) is an ideal choice for us without a special gain in the mast top.
Coaxial cable, plug
Especially by radio amateurs like to be told, you have to use high-quality, low-loss cables and special RF connectors. In her view, that’s completely true. In maritime radio, it is not about a few meters more reach beyond the visible horizon beyond but with simple means to make secure connections. For lengths up to about 15 m simple RG 58 coax cable is quite sufficient, only about three times as expensive Aircell 5 makes sense. Aircell must be processed very carefully. I know several cases in which the air pores in isolation have been soaked with water. That was it with the good RF characteristics. This does not happen with cables with PE insulation such as RG 58 or RG213.
It is the same with the plugs. If expensive N plugs were really necessary, they would also be on the devices. However, there is not a single device in the VHF maritime radio sector that does not have a standard SO 239 aerial socket. On it belongs a plug PL 259 and nothing else. It is important, however, that you correctly mounted. You can not discuss the necessary weather resistance. Water like all antenna plugs does not like. At the antenna itself, manufacturers make sure that the cable can be connected properly and the plug at the mast breaker belongs without any ifs and buts in the dry area below deck.
Antenna splitter and what else interested
Antenna splitter is used if you want to use the same antenna for several devices at the same time. This only makes sense if the antenna is also suitable for it. The picture on the left shows the circuit of a typical marine radio antenna. Via the oscillating circuit below, the antenna is adapted to the feeding coaxial cable. This only works on the marine radio frequency for which the antenna was built. She’s even good at that, while on other frequencies she does not work at all.
On the contrary, these areas are deliberately suppressed. It makes no sense to use a splitter on such an antenna to even operate the radio, the TV, or even the mobile phone. This is different from a spacer for AIS since AIS works in the same frequency range.
Although an AIS splitter would overcome the slight losses, I am not a friend of such devices. A splitter is just an additional device, which can fail. Plus, it’s about three times as expensive as another antenna. Therefore, I would prefer a separate antenna for AIS.
The diagram also shows another feature of the antenna, which becomes clear only at a second glance by connecting the core of the cable to a tap of the coil results in a short circuit for the direct current of a conventional multimeter. So you can easily check with such a device, as it has every skipper on board, whether the antenna is properly connected. Interruptions of the line are among the most frequent errors associated with antennas.
In Seglerkreisen one hears again and again of alleged rules according to which for radio devices an own battery and double safety and shut-off should be prescribed. That may have been like that in the old days. I can not say with certainty whether it is still the case on equipped ships today. On sports boats, it is in any case customary to connect the radio, usually together with the GPS from which it relates the position, via a switch of the main distribution to the normal onboard battery. Therein I see no problem, especially if you have an additional independent of the power supply handheld radio like me.
The connection of a GPS
A DSC emergency call with the push of a button at the same time the current position is transmitted requires the connection of a GPS. DSC marine radios almost all have an NMEA input. As a GPS you need accordingly with an NMEA output. Many devices can do that in the so-called. GPS mice, which are intended for connection to a PC, you have to make sure that they have not only a USB connector but also an NMEA connector. Often an adapter or another cable is necessary for this.
The NMEA protocol is standardized and ensures traffic. Unfortunately, there is no universal standard for the connection of the pipes, which sometimes leads to difficulties. But there are only two lines to connect. In the manuals of the devices, the NMEA interface is described exactly. One line is the NMEA signal. GPS is the transmitter. So we are looking for a line there, which is something with TX usually with an addition such as NMEA, RS 232, V24, and possibly also a “+.” Sometimes the term is simply TXD or TXOUT. This line is connected to the NMEA receiver on the radio. There, the line is usually referred to with RX and corresponding additives. The second line is the reference potential. It’s often the same as the one but then with a “-.” Sometimes the name does not exist either. Then connect to Ground (GND). That’s all. Of course, it must also be ensured that the GPS receiver is connected to the power supply. This is especially overlooked in GPS mice and is a common cause of the error.