In the current landscape, more and more vendors are trying to move into the cellular space, wanting to provide clients with the ultimate 4G or 5G connection. VSAT providers are trying to give you the complete connectivity package, cellular modem manufacturers are slipping in the SIM card option, and vice versa 4/5G SIM card suppliers add the perfect antenna option to their monthly subscriptions.
All of them are touting the connectivity range that their solution will provide, and how many miles offshore you will still receive a signal.
When you consider who to go with, what hardware to install and which SIM card to use, I wanted to lay out a few basics that you should always keep in mind. From there the salesperson or the marketing material should only be the final turning point for you to choose who you believe in most.
I wont hide the fact that I can also assist you in a SIM card subscription, or the fact that the SIM card I supply is likely to be very similar to what others supply, but that is why you need to look at the whole picture.
Spotlight on the superyacht antenna
I will go from top to bottom. The antenna is a crucial part of the design. It comes in various types and shapes, with the dB performance number being the most crucial. Be clear that a passive antenna will always output the same power, no matter what enhancements are made to it. The improvement in performance comes in shaping the RF emission of the antenna. i.e. the “beam” is shaped to change the reach of the antenna which improves the performance in one direction at the expense of decreasing it in the other direction. That is why a dish antenna can reach out into outer space, whilst an omni-direction antenna (normally a vertical stick antenna) would not be able to.
That said, you can get very nice 7-8dBi omni-directional antennas that improve their performance by flattening their beam i.e. decreasing the spread in the vertical plane, whilst increasing it in the horizontal plane. This means it reaches further.
How much further? Well RF needs line of sight, as any obstruction will decrease the performance, and if it is a metal obstruction, even more so. In other worlds, the higher the better, and the same goes for your vhf antenna.
Now, a bit of mathematics. Let’s say both your mast and the cellular mast on shore are 40m high, giving it a 28nm distance. A search on the internet for a RF line of sight calculator will give you a place to enter these numbers if you want to double check. Anything above that number has obstruction. (Note we are calculating the distance between two antennae, not the shoreline and your vessel.
The next important factor is the cable run between your antenna and the modem. The longer it is, the more loss. The more connectors there are, the more losses. The more cables run parallel to each other, especially electrical, the more influence on losses. Get the picture? Simply said, the closer the modem to the antenna the better the output performance, as every decimal of a dB is a gain. 3dB is half the antenna power. A connector in itself can be 0.5dB (or more) loss.
This is why you see more and more modem manufacturers trying to sell you a “dome” antenna where the modem is physically built in the same housing. The problem is the SIM card normally needs to be slotted in at the modem, which in this case is up the mast! But there are solutions for this.
Different types of SIM card
SIM cards, or those little plastic pieces with strange metal engravings, come in various types and they are bound to various performance factors. This has to do with the network provider and the agreements they have, and how the card registration is programmed into their system.
A business grade card outperforms a consumer grade card. It has higher priority which is why it costs more money. A local card has priority over a roaming card, as that is the privilege of the local operator. An unsteered card will search for a better signal, while a steered card will be bound by best agreement rules (i.e. a network operator will have a better agreement with one overseas operator than with another, and thus steer you to their favoured business partner). This means you may get a weak signal, while others around you have a stronger signal.
Shared networks
The last factor that strongly influences the performance is how many modems are sharing the same network. This has nothing to do with signal strength or SIM card performance, but rather bandwidth from the cellular provider at the antenna mast that everyone is trying to connect to.
I have not spoken much about the modem itself here as that is a completely different article, but there are a few dominant manufacturers out there. What you need to make sure of is that you have one that is multiple antenna (MIMO) and of at least cat-12 specifications, for the region that you operate in.
So, when they sell you that 80km range, do ask what their tests are based on? And will you have exactly the same environment on your vessel wherever you intend to be sailing?
Please contact Tim if you have any AV or IT questions (he won’t charge or bite for simple questions!) or if you need technical support and training for crew assigned to look after their AV & IT system on board: Virtual AVIT ETO, teletechnics.com.
Written By: Tim Gorter
