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Old 03-05-2018, 03:53   #1
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Cellular Repeater

At the heart of our new instrument system is a ship's computer which is hard-wired by Ethernet to a Teltonika RUT950 router. The router is set up to connect as follows:-


1. Via external WiFi when that is available. The router is hard-wired to a Ubiquiti Bullet to bridge the WiFi signal so if the boat is within range it's usually going to be stable.
2. If WiFi is not available or drops out the router automatically tries to failover to a cellular connection on 3G, 4G, or 4G+LTE. It has two SIM card slots so if the regular cellular provider is flaky and someone else offers a better signal a "local" SIM card can be put in slot 2.


The router has its own pair of cellular antennas but it can't be mounted high enough to get the best possible signal. A suitable external antenna has been found, tuned to receive European 3G/4G/LTE frequencies, which can be mounted high on the mast. In this location it will stand a much better chance of picking up a good signal. But the cable run between the mast and the router is about 15m so there will be signal loss in the cable. Therefore a powered Repeater is needed which takes the signal from the antenna and gets it to the router with minimum loss. All totally hard-wired. No broadcasting involved. This isn't about "boosting" the mobile signal for phones. The aim is to give the ship's router (and therefore the ship's computer) the best possible chance of connecting to cellular data. Phones can connect to the router via the router's WiFi which gives us email and Whatsapp, and before long VoLTE (Voice over LTE).


The Repeater is proving difficult. Everyone I have spoken to so far is offering kit which is designed fundamentally to re-broadcast the cellular signal so that phones can pick it up more easily, and that's not what we want. When I ask about hard-wiring Repeaters to the router's male SMA antenna connections all I get is waffle. Nobody seems to know whether the boxes they are selling will do that or what the cable specs might be. Some of them aren't even sure how near to the antenna their Repeater needs to be or how far it can send the signal to the router. Ideally we would have the repeater in an IP65 enclosure inside the equipment space at the foot of the mast, about half way between the antenna and the router measured by cable run. Another problem is that when I ask what cellular frequencies a product supports I don't get coherent answers and the published technical data for what I've been looking at leaves a lot to be desired. I've seen "5 band repeaters" where there is no data for what the bands are. I sometimes get the feeling that I know more about this than the vendors which would be funny if it wasn't so frustrating.


I ran a search on here and couldn't find much but I'm hoping that someone has solved this problem. Thanks.
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Old 03-05-2018, 05:04   #2
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Re: Cellular Repeater

You might consider putting something like these outdoor LTE routers up your mast. This would allow you to use an external antenna with a short coax run and use ethernet cable to get the signal below.
wAP LTE
LtAP mini LTE

They also have versions that let you put the PCIe modem card of your choice in them to get the bands you need.
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Old 03-05-2018, 05:08   #3
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Re: Cellular Repeater

What you are seeking is commonly called a BDA or BiDirectional Amplifier.

Google the phrase “cellular bidirectional amplifier”. Be prepared to read a lot.

I think the biggest problem you will have is OVER amplification. You MAY need to include one or two attenuators.

In the US there are some legal requirements about using such things that dont consider boats. Probably safe to ignore, but maybe why you are getting the “waffle” answers, even if the person knows, which is far from certain. They keep the true engineers in a closet and slide pizza under the door.

At the end of the day what you want to do is to overcome the cable loss. Have you calculated that and is it actually significant? You may be over thinking. In any case you need to know what loss you are trying to offset.

For a quick and dirty try you could buy a Wilson BDA, get the one with least amplification possible, and give it a go. My gut feeling is that would do the trick. They sell a range of BDAs. You will likely need to make the cables yourself or find someone to make the cable, they are available online. Anyway, for a few hundred bucks you can try it out.

If you go to TESSCO you can find most any type of cable spec. with loss ratings.
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Old 03-05-2018, 06:09   #4
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Re: Cellular Repeater

Thanks for the suggestions. I am following them up and will report what happens.
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Old 04-05-2018, 21:41   #5
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Re: Cellular Repeater

TwoHooter,

The over-amplification issue is real; the LTE transceiver should not report more than -40 dBm RSSI (received signal strength indication). Over that and you may be creating issues. BDA's are built for specific bands, with filtering to prevent out-of-band emissions. Which bands is country-specific, as seen on Wikipedia: https://en.wikipedia.org/wiki/List_of_LTE_networks

The BDA manufacturers, like Wilson Electronics, have to pick the most common bands that can be easily manufactured and that will sell well.

The BDA will attempt to overcome the cable loss. But you can also use a lower-loss cable, like LMR-400.

You should find out how much signal you are receiving and if possible, the SINR value.

The other option is a higher gain antenna. This is tough on a boat, because the way to get higher gain is to narrow the beam. That means you have to point the antenna accurately, in azimuth and in elevation. Modern LTE radios, like advanced WiFi transceivers, are beginning to use more and more antennas, allowing beamforming. But this is beyond a boat installation.

Antenna height is your friend, but then there are Fresnel zones; sometimes you need to pick a different height to avoid signal cancellation.

John
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Old 05-05-2018, 05:56   #6
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Re: Cellular Repeater

Thanks to all.

W32 Pamela - good idea but I don't fancy climbing the mast and opening an IP67 box just to change the SIM card when we need to use a local PAYG service .

hpeer - I think this is going to have to be a bit of a trial and error thing. Hopefully not too expensive on the error side.

John -
Quote:
Originally Posted by torrmundi View Post
TwoHooter,
The over-amplification issue is real; the LTE transceiver should not report more than -40 dBm RSSI (received signal strength indication). Over that and you may be creating issues.
Am I right to think that the router will report the signal strength sufficiently accurately to check for over-amplification (in its admin pages)?

Quote:
Originally Posted by torrmundi View Post
BDA's are built for specific bands, with filtering to prevent out-of-band emissions. Which bands is country-specific, as seen on Wikipedia: https://en.wikipedia.org/wiki/List_of_LTE_networks The BDA manufacturers, like Wilson Electronics, have to pick the most common bands that can be easily manufactured and that will sell well.
Yes, I've been learning about that, in fact I ended up writing my own idiot's guide to cellular radio communications because I couldn't find the information I needed all in one place. Some of our boating friends keep their boat in a marina and just make excursions, typically 20 to 200 miles. They can use just the bands that cover their area. But we don't have a home port, we cruise continuously, around UK and Ireland up to now but to Europe soon. Most of the bands in our waters are the same and hopefully the antenna will cover them OK, also the BDA if we get one. This must be a nightmare for bluewater cruisers trying to get a better signal on totally different frequencies.
Quote:
Originally Posted by torrmundi View Post
The BDA will attempt to overcome the cable loss. But you can also use a lower-loss cable, like LMR-400.
The electrician who is helping me with this says even the best cable in the world won't handle a 15m run from external antenna to router.
Quote:
Originally Posted by torrmundi View Post
You should find out how much signal you are receiving and if possible, the SINR value.
Signal to Interference plus Noise?
What instrument is used to measure that?

Quote:
Originally Posted by torrmundi View Post
The other option is a higher gain antenna. This is tough on a boat, because the way to get higher gain is to narrow the beam. That means you have to point the antenna accurately, in azimuth and in elevation. Modern LTE radios, like advanced WiFi transceivers, are beginning to use more and more antennas, allowing beamforming. But this is beyond a boat installation. Antenna height is your friend, but then there are Fresnel zones; sometimes you need to pick a different height to avoid signal cancellaon.
We do have some height. The boat is a Nordhavn 40 with a mast like a yacht. Top of the mast is 27'7" (8.4m) AWL and there's plenty of scope to add brackets, so we are better off than most motorboats. Pointing the antenna sounds like a job for an electric gimbal like a powered satellite dish but I haven't found anyone offering those. I also found out about Fresnel zones when I was reading around. I'm pretty sure that putting the antenna as high as possible will be the right solution most of the time, but of course that creates the cable loss of signal problem.

Michael
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Old 05-05-2018, 06:28   #7
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Re: Cellular Repeater

Finding a wide band high gain antenna to cover most if not all European cell bands can be accomplished.

Utilizing an amplifier like you are looking for is an issue. First are the frequencies, and second is the legality of doing so. Wilson, who makes cell boosters in N America, has gone through many iterations of product development and FCC/carrier approval to design their current round of products. Their boosters have quite a bit of logic built into them that you would never be able to reproduce with a simple amplifier. Even if you can adjust the amplification, it won’t meet any standards/regulations. I do not know specifically of the EU regulations, but I am sure there are some regarding cell amplification/boosters.

No question 15m of coax is a bad idea. Will eliminate all benefit of mounting the antenna high, and the gain provided from the antenna. But, your statement of the higher the antenna the better, is not necessarily accurate. By far the most important factor is the physical obstructions between your antenna and the antenna on shore. Height has value, but don’t go overboard. Perhaps a lower mounting location is the compromise for you, or re-thinking the router installation location.

I understand you are not a fan of accessing the SIM card outside, but getting the radio closer to the antenna is the best (if not only) solution.

Cell carriers monitor their towers 24 hours a day for anamolies. And if an anamoly is present for a period of time, they will physically come find you. We had experience with this with a customer of our cellular product who mis-installed something. AT&T showed up at his boat, in the USVI (they flew in). The carriers are extremely meticulous about their networks.
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Old 05-05-2018, 08:22   #8
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Re: Cellular Repeater

As to antennas and practicality... first you are on a boat. So forgot high gain antennas that need to be aimed. Get the best high gain OMNIDIRECTIONAL antenna you can.

Also forget about Frenel zones and such. Yes it is real, but you are on a BOAT that moves. No way you can account for that with a directional antenna.

I’m not sure what you mean by “electrician” and he might be really well qualified, but the moniker “electrician” does not denote, on itself, any special qualification.

What you are absolutely right about is this taking some trial and effort.

No matter what you do you will simply be making the situation “better”, never perfect. The cost of getting the “best” system is likely to be marginal, maybe not even noticeable.

Now I’m gonna tell my story, which is different from your story, but may be usefull, hopefully. Our needs and motivations are different. My Wife, now retired, worked by phone, no phone, no trip. PERIOD! What a huge PITA. I have cruised from Labrador through the Eastern Carribean.

First we have Verizion which has Travel Pass. They have agreements with most places. Canada/USA/Mexico are all as one area. Outside we can connect for a 24 hour period through a local provider for $10 with unlimited voice and 500Mb of data. I bought a Wilson repeater, gained for a small house, and a magnetic mount Omni antenna, Steel boat. She takes this contraption with her on both boats and to our hunting cabin.

If signal is too low I set up the repeated and plunk the antenna down on the coach roof. If I still can’t get signal I run it up the masthead on a halyard, stick a bit of plate steel to the magnet to make a counterpoise. That has got me through a few years of cruising in some pretty remote areas. To be honest we don’t use it much because we generally have sufficient signal.

So think about that, I’ve got the antenna at my mast head run into the cabin. I’ve got at least 15m of cable strung out, and it works. So that’s pretty good evidence that 15m of cable is not a deal killer in itself. Second I’m using a jury rigged antenna, if you get a high gain OMNI and properly mount it you can do better.

So I’ve sunk maybe $250 into my solution, I had to have a special cable made to convert cable attachments.

My suggestion is to get the best high gain OMNI you can, use good low loss cable, and give it a try. That is all a good investment. THEN if that doesn’t work look to a BDA.

But let’s put some numbers on this.
What cable are you using and what is it’s loss at that band?
What is the best OMNI antenna you can buy and what is its gain?
Then we have something more substantial to discuss.
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Old 05-05-2018, 08:29   #9
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Re: Cellular Repeater

Here is a good loss calculator:

Welcome to Times Microwave | Coaxial Cable - Attenuation & Power Handling Calculator

(high and low cell frequencies, plenty in the middle).

15m LMR400 at 700Mhz: 2dB
15m LMR400 at 2700Mhz: 4dB

LMR400 is a real pain to work with, but certainly is a viable cable, and really the only choice for a 15m run if looking for as good performance as possible. Certainly other cables will work, just with more loss.

The highest gain "real" omni you will find in a wide-band format is 4-6dBi. If you see numbers higher, approach with skepticism.
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Old 05-05-2018, 08:33   #10
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Re: Cellular Repeater

The other part of this is how you intend to use the installation: is it a MUST have?

Then the part I know nothing about: what service providers are in your cruising area and what is their coverage like?

For us Verzion provided a needed service to bridge connections into foreign countries. I don’t know if such a service exsists in your cruising area.

I’m just trying to compare my experience to yours, we have been in some pretty remote spots and done OK. I’d be surprised if your coverage is worse than ours.
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Old 05-05-2018, 08:40   #11
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Re: Cellular Repeater

Quote:
Originally Posted by kiltym View Post
Here is a good loss calculator:

Welcome to Times Microwave | Coaxial Cable - Attenuation & Power Handling Calculator

(high and low cell frequencies, plenty in the middle).

15m LMR400 at 700Mhz: 2dB
15m LMR400 at 2700Mhz: 4dB

LMR400 is a real pain to work with, but certainly is a viable cable, and really the only choice for a 15m run if looking for as good performance as possible. Certainly other cables will work, just with more loss.

The highest gain "real" omni you will find in a wide-band format is 4-6dBi. If you see numbers higher, approach with skepticism.
There you go, it works out to just about a net 0dB link loss. He will need some custom adaptor cables at least on the equipment end to transition from LMR400.

The install will be a real PITA but it’s a good solution without added equipment. Loss coat, high reliability. I like it, provided I don’t have to install it.
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Old 07-05-2018, 07:57   #12
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Re: Cellular Repeater

Hi everyone. I am reading the replies, thank you all very much. I'm running the same question on the Nordhavn Owners Group and the UK YBW motorboat forum. It's been really interesting to see all the different responses. Clearly some trial and error is going to be called for and I'm up for that. I will report back.

Two things I will say now. First, the electrician who has been installing our new electronics suite is very good. I designed our new system but he has made it work, and I think we may be the first Nordhavn with no chartplotter. Everything runs off the ship's computer with iKommunicate as the NMEA interface, and our main navigation software is OpenCPN (with Coastal Explorer installed as a secondary system). He is the one who is worried about signal loss in a 15m cable and got this whole Q&A thing started.

Second, why do we want this? We have a reason for wanting to do all we can to enable us to monitor the boat when it is left unattended, whether that is for a day at anchorage while we go walking ashore, or a month's berth in a marina or (more likely with us) fishing port. We could afford the capital cost of a KVH miniVsat. but not the subscription charges. Interfacing the ship's computer with Iridium looks like a nightmare. So the practical alternatives are an occasional solid WiFi connection, and cellular. I'd go so far as to say that if we need to leave the boat for a while we'll probably let the connectivity be the deciding factor. Some of the places we have left the boat have no or poor WiFi and poor cellular. A good example is Penzance Harbour, but if you walk out of the Harbour and up into the town you get 5 bars. I'm confident that with a cellular antenna at the top of our mast and negligible signal loss to the router we would have an adequate signal even in places like Penzance, and that is what this is all about.


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Old 07-05-2018, 14:55   #13
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Re: Cellular Repeater

In US English, a repeater is a bidirectional radio, which on the cellular system would be called a "picocell" or "femtocell" meaning a small cellular "site" that locally relays signals into or out of your phones.

But since you want hardwired, that puts you back to an "amplified antenna" or as others have said, in this case a bidrectional amplified antenna. That's going to be hard to find, if they exist. Probably because there is no (or very little) commercial market for them, while the picocells and femtocells are very commonly used, and require no installation skills or expensive cable runs.

If you can't find a bidirectional amplified antenna, you may have to consider having one built, or trying a compromise like six feet of cable and a higher gain antenna mounted on deck rather than aloft. Sometimes just getting the antenna out of the cabin gives you enough extra gain to make the connection.

The other alternative for remote monitoring would be one of the systems using satellite communications and text messaging. Not streaming video, but a much larger coverage area.
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Old 10-05-2018, 05:38   #14
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Re: Cellular Repeater

@ hellosailor - Satellite is on the wish list but not an option at the moment due to the subscription costs.

The current plan is to adopt the suggestion made by W32PAMELA, the first reply on this thread, and endorsed by hpeer's experiences. The existing router is going into in an IP66 enclosure to be fixed at the top of the mast, together with an easy way of climbing the mast, a proper work platform to stand on, and fall arrest gear to make me feel safer. I need all that anyway. I probably won't need to change the second SIM card very often so I'll live with that. The masthead 4G router will have very short cables to either its own antennas or a new omni. Shielded Cat5 cable (with Power over Ethernet) was installed inside the mast yesterday to connect the masthead router to a new simple ship's router in the wheelhouse. Much easier to install this than LMR400 low-loss co-axial cable. The second router is needed because the ship's computer and another router serving cameras inside the metal-lined engine room are both hard-wired by Ethernet. This is an experiment and we will see whether it works. All the repeaters seem to be illegal in our cruising area - the only legal option is an in-vehicle repeater which just isn't worth bothering with. I will report the results. Thanks again for all the advice.
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