Multiple 4x4 MIMO antennas on HD4-MBX Cat 18

Hello, I have a few questions related to antennas. Most are related to a setup for an HD4-MBX Cat 18 except for the first.

From (I think) roughly easiest to most difficult…

  1. I’m looking at also purchasing a Transit Duo Cat 12, which has two modems and 4 cellular antenna ports. Occasionally I see references to using a single 4x4 MIMO dome antenna to serve two modems. Is that advisable? It’s certainly more convenient, but is performance lessened compared to two separate 2x2 MIMO antennas?

  2. Can multiple antennas share the same ground plane, e.g. a single large sheet of metal?

  3. According this this forum post (MBX CAT18 Antenns MAX-HD4-MBX-GLTE-G-T) the different antenna ports on the HD4-MBX Cat 18 are best tuned to different frequencies. Is that true? It doesn’t seem to be called out anywhere else.

  4. The big one I’m struggling with, regarding spacing between separate MIMO antennas. I want to install the HD4-MBX into a portable Pelican-style case. However, unless someone can point me to something different, the HD4-MBX Cat 18 requires 4 separate 4x4 antennas. The rep I worked with suggests that the antennas be spaced “1’-2’ apart”. The most obvious answer is a case that is 24"x24" with the antennas located at each corner; once you factor in the ~5" diameter of each dome, they’re about 18 inches apart.
    The problem is, those 24" square cases are quite large and heavy. There’s a significant difference in weight and construction between a traditional rectangular case in the 20"x14" range and the 24"x24" cases.
    So my question is, do I really need that much distance between the antennas? FYI the priority will be upload speeds, so I can see transmit interference being a concern.


  1. I’m using that same Telit LM960 cat 18 chipset in a Max Transit and it switches between 4x4 MiMo B2, B66 and then 2x2 B30, B5 on a regular basis, so I wouldn’t install frequency dedicated antennas thinking it will stay consistent.

As to the other questions, someone more knowledgeable can answer, but my view is trial and error is your friend. Is a 1-2% speed difference worth placing 4 antennas 4 feet apart versus the simplicity of a single 4x4 mimo? For most people convenience wins, but for a few they want every last drop of speed or reliability. I ran my antenna indoors for years and then finally decided to punch a hole and place it outside. The result was zero change in speed, but a 10db stronger signal. Was it worth it? who knows… it’s probably more reliable on rainy days now, but speed wise it gained me nothing. Antennas are like the dark arts… stand on one foot and look sideways for them to work properly :slight_smile: this whole multiple path that MiMo provides makes them hard to predict. I have a copy of someone’s doctoral thesis that says ideal placement for MiMo is 7 wavelengths or greater apart.


In theory no - especially if both modems have SIM from the same carrier so are using the same frequencies, since the elements are very close together and would potentially interfere. In practice I see a lot of installs doing this sucessfully, If i were to do it I tend to manually set the allowed frequencies per modem / element.

I design and build enclosures for MAX routers (BR1s, Transit Duos mainly) professionally. Sold hundreds of them globally. What we used to do was space stock antennas with as much horizontal and vertical separation as possible. Over the years we got better at antenna placement and then we had a custom antenna manufactured for us that took that experience and made the form factor easier.

Keep them as (socially) distant as possible (in the horizontal and vertical planes), position them at 45> 90 degrees to each other and test. You’ll be fine.


Thanks Martin, I was literally just looking at your website and blogs/videos when I got this response. Fantastic stuff!

So two thoughts come to mind:

  • With 4 4x4 dome antennas, would it make sense to place two horizontally inside the case, and two vertically on the lid? I assume at least with the standard domes the underside of the domes (the back side of a lid if they’re mounted on there vertically) do not have great signal.

  • An idea I just had an hour ago, following a revelation that a 4x4 antenna is really two pairs of 2x2 cross polarized antennas. In order to increase spatial diversity between those two pairs of 2x2, would it improve performance to split modems between domes? E.g.

    Modem One, Dome 1 Pair 1, Dome 2 Pair 1
    Modem Two, Dome 1 Pair 2, Dome 2 Pair 2

That make sense? It seems obvious to me but I don’t recall seeing it mentioned anywhere.

No idea. Depends on your case layout, whats inside that will block signal etc. There is no shortcut to this but to look at what others have done and stand on their shoulders and try it. Go check out Peter West’s speedfusion cases, he is a bold innovator in this space and I bet you’ll learn a lot from studying his work.

Not sure it would. The whole point of carrier aggregation is to combine multiple different frequencies to improve bandwidth, so a CAT 18 modem would never want to have its 4 x mimo channels using the same frequencies. a modem per dome seems to make sense (if domes make sense at all in your build- why not use some flexible PCB antennas?) rather than risk mixing channels from different modems that could end up clashing.


Good point re carrier aggregation. Thanks for the links, definitely checking them out. Ironically I’m working on a completely separate project that involves PCB antennas, didn’t think to see if that was an option for here too. Thanks!

We also struck the problem with having 16 antennas needing to be mounted in restricted location (in our case yachts) Our solution was to mount them on 4 different levels with stainless steel groundplanes within a single satellite dome.
With the coronavirus restrictions easing here now we hope to get some real world testing shortly
Spec sheet:


Damn that looks beautiful! It’s not any more portable than what I was originally thinking, but it sure is more elegant. Definitely getting the brain juices flowing. Is it available for purchase (without the HD4 which I already own)? FYI the spec sheet isn’t publicly accessible, it’s asking me to request permission to view, which I don’t want to do if it’s someone not expecting the request :slight_smile:

Ah sorry about that - my fault for having 2 files with the same name on my drive. I’ve updated it now. There’s also a video on our facebook page which goes into a little bit more detail of what we did. Yes they’re available for purchase, and we’ve got our testing now lined up so we should have some real world results in the next couple of weeks.

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I love the easter egg in the datasheet :wink:

What’s the facebook? I’m unable to find it when searching for variants of “horizon hosting” or “horizon marine”.

I’m not sure if linking to facebook works but here goes!


That’s beautiful. Not at all related to my original questions, but with the fan and the air gap isn’t their concern about corrosion from the sea air? (I have no marine experience…).

You’re going to need some sort of ventilation if you’re intending on mounting one of the HD4’s, in particular the HD4MBX’s in an enclosed space. In our case the air is drawn from the (normally void space in the mast) base and blown out the crack - it’s positively pressure keeps the salt air from coming in. It’s probably also worth noting that it’s going to be normally mounted 20M+ above water level haha.


That makes perfect sense, thanks!

Hello @shownet
Here are a couple of previous posts on some of the new antennas we have been using/testing and also discussing antenna spacing.

The antenna solution from @Horizon is impressive; we are very interested in getting these into Australia, an efficient & functional design.

Happy to Help,
Marcus :slight_smile: