MAX HD4 LTE Diversity/aux Antenna port

What is it for?
Is it a required connection?
will the band antenna’s that were included with it suffice; though the actual antenna is an exterior YAG?

Please check the following knowledge-base:

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Just testing this on an HD4.
We have 2 x 4 into 1 splitters with all the main antennas on one splitter and the aux on the other.
We have a SIM card in Cellular 1 slot A.
When we disconnect the Main antenna, the Aux does not provide a backup and the connection is lost. The SIM card goes back to a disconnected state and searches for a provider.
We had the same result on Cellular 2.
We are on the latest firmware and in all other ways the HD4 is performing well.
Is there something we need to do in the setup for this to work?

AUX I thought was receive only (no transmit)… it allows for receive diversity to help improve the signal quality.

In fact, the FAQ says this specifically:

Note: The main antenna is used for transmit, and both Main and Aux antennas are used for receive.

So when they say ‘acts as a backup’, that implies they both transmit… which is false. You MUST have Main attached for the modem to work.

Hi Doug.

Thanks for that. I can move on with the testing.
I presume each Main antenna is tied to each SIM slot, so if I am using Cellular 2, I assume that I could disconnect all antennas except the Main one for Cellular 2 and the system should still work? Or???

Correct, that’s how I understand how it works as well. Each modem inside the router is directly connected to its respective main/aux ports on the back.

Hello @CCNP_Mark,
Can you confirm if you are using a RF Signal Splitter or hybrid coupler network for sharing your antennas modems?

We advise agains using an RF Signal Splitter to connect multiple modems to a share antenna, instead you should be using a hybrid coupler or a hybrid coupler network.

The reasons are very simple for this, the modem is designed to be receiving low power levels from an antenna, yet when you use a spliiter you are connecting the higher power transmitting of another modem almost directly into the the receivers of the other modems, this can cause an increased noise floor for the receiving modem as well as expose the receiving modem to excessive power levels from the transmitting modem. Also a splitter will be dividing the antennas receive power and the modems transmit power by aproximatly a factor for 1/N (N being the number of connections). A good quality Hybrid coupler generally only has a 3dB loss and does not pass RF power between the devices, only to the antenna.
We recommend using the RFI Wireless Hybrid Coupler 698-2700MHz 3 dB 716 DIN Type

In connecting your external antenna, most cellular antenna systems for MIMO work best with an out of phase antenna array (+/- 45 Degrees of the vertical), meaning you can have a very tightly packed antennas with exceptional performance.

We suggest that you contact your local Authorised Peplink Partner for specialised assistance.

Your local Certified Peplink Partner can help you with a copy of the Antenna Selection Guide for Peplink Partners, this is a detailed guide and is only available to the Peplink Partners so to ensure that you are helped in working through it to get the most suitable antenna solution to your application.

Remember that the majority of these systems are MIMO (Multi In, Multi Out), so you must ensure you use antennas and cabling & and RF network that are suitably designed for the application.
Happy to Help,
Marcus :slight_smile:


Hi Marcus.

Thanks a lot for the information. The splitters and antennas I use were supplied to me by an ISP that I trust but I will be checking their parts specifications in light of what you say. The ISP are experienced in these sorts of installs and I am unaware of any issues arising from taking their recommendations.

With regards to the antenna positioning the installs I look after are Marine vessels and whilst having antennas at 45 degree angles to each other might be optimum, invariably there are other reasons why I may not be able to make this happen, but I will make the recommendation for all future installs now that I have it.
Thanks again for the info.

Hello @CCNP_Mark,
There are lots of skilled professionals working with ISPs, our experience with them is though they are trained on the broad basics and are not able to become high level specialist in a chosen area, this is were the comunity of Peplink come in to play, none of us here are can know and be everything, yet we all are here and with our combined learings will share so to help the greater Peplink Community.

Here is an extract from the Antenna Selection Guide around Marine Antennas.

Again refer to your local Certified Peplink Partner for more from the guide.
Happy to Help,
Marcus :slight_smile:

Are there any recommended MIMO antennas for marine/mobile use? I’ve inquired of my partner but they didn’t offer any up. Also, with a router like the EPX that can do 18X LTE modems, that’s 36 coax lines needed… is there any solution to share a cluster of antennas and feed all the LTE modems simultaneously, while also allowing for MIMO that LTE can take advantage of?

Hello @DougHecka,
The best MIMO omni antennas are not easily sourced as a rule except to high end users, they are normally used for small cell installations and come at substantial price, not to mention they can be very bulky and heavy, so may not be suitable for a small boat.

Here are some URLs to help you with finding MIMO antennas.

From Telco Antennas (an Australian designed antenna for mixed environments) is this omni directional MIMO antenna

From CommScope
Filtered search for Omnidirectional Antennas

Filtered search for Small Cell Antennas

In Regards to a professional designed RF network for the EPX (and anything more than a HD4), this is something a professional & experienced cellular RF Engineers can design on a per application bases for you, be prepared that the design time is going to be chargeable and that you could be looking at several thousands for the design and that is before the equipment is made, please contact Peplink Sales and ask to be put in touch with a suitable experience cellular RF engineer if you would like a solution designed and costed, Peplink will do what they can to help you.

FYI, a summary of the theory involved in design RF Networks around Hybrid Couplers can be seen at Wikipedia

Happy to Help,
Marcus :slight_smile:


Awesome, thanks for the information. In this case, I’m looking at 3+ ‘boats’, the largest of which carries over 500 pax/crew, all of which demand an ever growing need for bandwidth. Part of the solution may be adding a distributed antenna system for the cellular bands so there’s less demand for our own bandwidth… right now the only internet some areas on-board get is via our Wifi APs. Cellular just can’t penetrate into a giant floating metal box (filled with smaller metal boxes with metal doors) effectively, especially when underway in rural areas.

Side note, we’ve reached out to Peplink before but always got referred back to our distributor. I’ll try contacting again and see if I can get any further, asking for a RF Engineer might get us on a different track.


What would be the correct way to connect two external antennas into the four modems of an HD4, main and aux ports, using hybrid couplers?
What would be the network topology? Are there anything like 4-way hybrid couplers or you would use them in cascade sort of topology?

Hello Nacho,
RF Networks are complicated and need to be carefully thought out and built to fit the solution required. A solution needs to take into account the location, frequencies, cabling, antennas, power levels, active electronics and interferences just to get started.

Always go for a separate wired antenna before anything else per modem connection, with the Pepwave MAX HD4 that is eight connections (or 4 x MIMO antennas).

Your best team to help you with this will be your local Peplink Partner (or local distributor) and their experienced RF engineer. There are a lot of variables and just putting together some pieces of equipment is not recommended with the HD4s (or other multi modem routers).

As an example, if you were to use Hybrid Couplers, expect to pay about $500US and up for good quality units. You are going to need six of them plus a whole bunch of other components. A custom-designed and built hybrid coupler for use with this many modems can cost over $3000US.

Then there is the antenna that you will be using and the cabling between the antenna and the rest of the components, remember to include lightning protection.

If your local Peplink Partner can not help, use the contact form on the Peplink website to reach out asking to be put you in touch with someone suitable. There are some exceptionally skilled and experienced RF technicians and engineers in the Peplink community. Please understand though that this knowledge is also a valuable commercial resource to them, so it is unlikely to be freely given, so expect to pay for a professional solution from any of them.

Happy to Help,
Marcus :slight_smile:

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Hi Marcus,

Many thanks for your answer. Yes, I understand that the ideal setup is one antenna for each modem port, but sometimes you can’t place 8 or even 4 antennas because of practical space or like in the private yacht industry aesthetics sometimes comes first.

Of course, I do not expect to have a complete solution for free, sorry my question was a bit wide maybe. I’ve seen setups with 4-way divider/combiners or with gain control amplifiers in between but I wasn’t familiar with hybrid couplers.

As far as I understand a hybrid coupler (unless is custom made) only comes with 4 ports, meaning it “splits” in 2 or combine 2 inputs into 1 output. Ports are isolated because lines just pass close to each other and don’t actually touch, which might be more efficient than a resistive isolation like in a power divider. But I’m still doubtful by looking at these parts specs as the insertion loss and isolation is almost the same:

I guess this is material for another post and further investigation and testing.

There are smaller boats that have 8 antennas. Larger yachts can have 1-2 dozen antennas. Dont know what the big deal is about making a mount to hold four MIMO cellular antennas? You can perhaps even build a custom dome or enclosure as long as it wont interfere with the signal.