Choosing antennas for 4x4 MIMO on Chateau LTE18ax

[MeltdownSpectre]

Hi all,

Been lurking on this forum for a while, learnt a lot about mobile broadband here and now want to upgrade the existing setup at our other house.

Disclaimer: I am not from Ireland, nor do I live there. Just decided to post here because everyone seems really knowledgeable about this stuff.

There's no fixed-line internet out there, so no DSL or cable or FTTH.

Currently have a Huawei B535-232 with a Poynting XPOL-2-5G antenna mounted on the roof. Gets about 30-40 Mbps over LTE on a good day, however I believe that's because the B535 is only using a single band (B3 1800).

The carrier we're using has enabled 4x4 MIMO, 256QAM and 2xCA (B3 1800 + B8 900) on the mast we're nearest to, but the B535 doesn't seem to support B3+B8 aggregation or any other features. They also plan to re-farm old 3G spectrum and launch 3xCA in that area as well (B3 1800 + B8 900 + B1 2100).

Just ordered a Mikrotik Chateau LTE18 ax, along with some U.fl to SMA pigtails to do the 4x4 MIMO external antenna mod discussed here.

I've got two antennas already, the Poynting XPOL-2-5G (directional) and the older Poynting XPOL-1 (omni-directional). Would it be possible to combine both of these, seeing as one is directional and the other is an omni antenna and because both have very different gain levels?

If not, what would be a good antenna to combine with the XPOL-2-5G for 1800+900 MHz CA, and potentially 2100 MHz whenever it's available on this mast.

Would appreciate any advice as to how the antennas should be mounted as well, I'm reading lots of conflicting information online and from various  YouTube videos.

Thanks

[Seán]

The Chateau LTE18 ax has 4 antenna connections on its modem, which greatly simplifies modding for 4x4 MIMO compared to the 5G model. 

I have not seen the inside of the Chateau LTE18 ax, however, it should have similar internal antenna connections to the 4G Chateau LTE12 model.  The U.fl ports for the 4G antennas will likely be named something like MIMO1 and MIMO2 with the MIMO1 pair having U.fl ports labelled Int and Ext for the internal / external antenna pigtails. 

You don't need to do anything with the internal MIMO1 ports as there are already two U.fl pigtails that connect to ANT2 and ANT3 on the back of the router.  These ports handle the primary MIMO of all the 4G bands and I recommend you connect your Poynting XPOL-2-5G to these ports.

   

To activate the rear ANT2 and ANT3 SMA connectors on the Chateau LTE models, go into Winbox -> Interfaces menu -> LTE Tab -> Modem button, then change "External Antenna" to "Both". 

For 4x4 MIMO, you will need to open up the router and disconnect the internal antenna U.fl connections for the second MIMO (probably labelled MIMO2), then connect your U.fl to SMA pigtails from those two U.fl ports to the empty ANT1 and ANT4 holes on the back of the router.  You can connect your omni-directional Poynting XPOL-1 to those ports.

You can mix different antenna types on each MIMO pair.  The antennas with the highest gain on the primary band should be connected to the main MIMO pair.  For example, Poynting EPNT-2 which is a 4x4 antenna with a router board enclosure is effectively a combination of the Poynting XPOL-2-5G directional and XPOL-1 omni-directional in the one antenna as only its primary MIMO antenna ports provide the high gain and the second pair to provide 4x4 MIMO.

[MeltdownSpectre]

The Chateau LTE18 ax has 4 antenna connections on its modem, which greatly simplifies modding for 4x4 MIMO compared to the 5G model. 

I have not seen the inside of the Chateau LTE18 ax, however, it should have similar internal antenna connections to the 4G Chateau LTE12 model.  The U.fl ports for the 4G antennas will likely be named something like MIMO1 and MIMO2 with the MIMO1 pair having U.fl ports labelled Int and Ext for the internal / external antenna pigtails. 

You don't need to do anything with the internal MIMO1 ports as there are already two U.fl pigtails that connect to ANT2 and ANT3 on the back of the router.  These ports handle the primary MIMO of all the 4G bands and I recommend you connect your Poynting XPOL-2-5G to these ports.



To activate the rear ANT2 and ANT3 SMA connectors on the Chateau LTE models, go into Winbox -> Interfaces menu -> LTE Tab -> Modem button, then change "External Antenna" to "Both". 

For 4x4 MIMO, you will need to open up the router and disconnect the internal antenna U.fl connections for the second MIMO (probably labelled MIMO2), then connect your U.fl to SMA pigtails from those two U.fl ports to the empty ANT1 and ANT4 holes on the back of the router.  You can connect your omni-directional Poynting XPOL-1 to those ports.

You can mix different antenna types on each MIMO pair.  The antennas with the highest gain on the primary band should be connected to the main MIMO pair.  For example, Poynting EPNT-2 which is a 4x4 antenna with a router board enclosure is effectively a combination of the Poynting XPOL-2-5G directional and XPOL-1 omni-directional in the one antenna as only its primary MIMO antenna ports provide the high gain and the second pair to provide 4x4 MIMO.

Thank you very much Seán.

Will take a while for my Getic order to arrive, but I'm eagerly awaiting the new router because I'm sick of the frequent dropouts with the old Huawei B535.

I watched a YouTube video by Dr Andre Fourie at Poynting where he explains antenna mounting for 4x4 MIMO. He suggests mounting the antennas on top of each other in rural areas, with a vertical separation of at least 0.6 meters or 2 ft.

In such cases, which antenna is to be mounted higher on the pole? The XPOL-2 or the XPOL-1?

Edit: Link to the video I watched:

https://www.youtube.com/watch?v=IO_KGrrWoAI

[Seán]

The XPOL-2-5G should go on top of the pole.

Ideally the XPOL-1 should not be mounted above the top of the house as this way the wall / roof will attenuate unwanted signals and interference coming from behind the antenna.

[MeltdownSpectre]

The XPOL-2-5G should go on top of the pole. 

Ideally the XPOL-1 should not be mounted above the top of the house as this way the wall / roof will attenuate unwanted signals and interference coming from behind the antenna.

Hi Seán,

I finally got around to opening the case on the LTE18 ax. I've attached some pictures below. I had two questions.

1) I don't think it'll be possible for me to attach the SMA connectors in the ANT1 and ANT4 holes on the back without removing the motherboard? Am I wrong for thinking this or do I need to remove the board?

2) None of the connectors on the board seem to be labelled, so I'm not quite sure which ones to unplug so I can replace them with the new SMA connectors+pigtails that I purchased.

Here's the Google Drive link for the photos, if you need photos of anything else, please let me know.

Thanks.

https://drive.google.com/drive/folders/1...drive_link

[Seán]

Those pictures are my first time seeing the inside of the Chateau LTE18 ax model.  The motherboard is larger than in the LTE12 model where it does not cover the rear SMA ports. 

From what I can tell, these are the two U.fl ports that you need to swap:

   

The other U.fl connectors on that side go through an antenna switch IC (the small black chips) to toggle between internal/external antennas for the primary MIMO.  The U.fl ports on the left are for the Wi-Fi.

It looks like you will need to at least lift up the motherboard to access the empty SMA ports underneath.  From looking at the pictures it should be able to lift up after removing the 6 Torx screws.  I don't think you need to remove the heatsink and you may able to lift it up enough without needing to detach the other coaxial pigtails.

Once you fit the SMA connectors, the pigtails can feed through the two holes on the motherboard directly behind the SMA ports.

[MeltdownSpectre]

Those pictures are my first time seeing the inside of the Chateau LTE18 ax model.  The motherboard is larger than in the LTE12 model where it does not cover the rear SMA ports. 

From what I can tell, these are the two U.fl ports that you need to swap:



The other U.fl connectors on that side go through an antenna switch IC (the small black chips) to toggle between internal/external antennas for the primary MIMO.  The U.fl ports on the left are for the Wi-Fi.

It looks like you will need to at least lift up the motherboard to access the empty SMA ports underneath.  From looking at the pictures it should be able to lift up after removing the 6 Torx screws.  I don't think you need to remove the heatsink and you may able to lift it up enough without needing to detach the other coaxial pigtails.

Once you fit the SMA connectors, the pigtails can feed through the two holes on the motherboard directly behind the SMA ports.

4x4 MIMO mod was successful, thank you for your help.

Unfortunately board removal was required, not entirely, but I didn't want to put too much stress on the other pigtails, so I had to remove some of them to give myself enough space to pass through the new pigtails through the empty ports.

The new pigtails I bought have slightly longer SMA connectors so they protrude more than the factory ones but other than that, they fit perfectly. 

[MeltdownSpectre]

Finally got around to setting up the MikroTik box.

Can not get CA to work for some reason, B3 and B8 work fine when enabled separately, but will not do CA.

B3+B8 CA works just fine on my phone (Galaxy S22 Ultra) and my fathers Galaxy A73.

Attached some screenshots from RouterOS. The device is on the latest EG18 modem firmware as well (EG18EAPAR01A13M4G).

One interesting thing to note is that B3+B8 CA worked fine when I tested the MikroTik box in an urban environment, but in a rural area it refuses to do CA on the same network.



If I leave LTE bands on auto or enable B3 and B8 only:



If I force B8 only:



Any thoughts as to why it won't do CA or anything I can try to force it to work?

Thanks.

[Seán]

There are two possibilities I can think of:

1. The mast does not allow CA from data-only devices such as routers to conserve the narrow 5MHz band 8 for phones. As band 8 can penetrate building material much easier than band 3, phones are more likely to use band 8 particularly in weaker signal areas.
   
2. The mast may require band 8 as the primary (upload) carrier for CA. Below a certain RSRP (usually around -108dBm to -112dBm) on the higher frequency bands, the eNodeB will hand the device over to a low frequency band, so your phone is more likely using band 8 as its primary carrier.
   

Unfortunately there is no way to force CA, however, you can try cell locking your router to the band 8 cell to see whether it will aggregate band 3 with the following command. First ensure the band selection is auto. This command is based on the cell ID and earfcn from above:

/interface lte at-chat lte1 input="at+qnwlock=\"common/4g\",1,3748,136"

To remove the cell lock:

/interface lte at-chat lte1 input="at+qnwlock=\"common/4g\",0"

Some mobile networks don't tolerate cell locking to a low frequency band when high frequency bands are available above a certain signal level. If this is the case the cell lock will cause the connection to cycle down and up as the network tries getting the modem off band 8. However, even if this works, this will likely cripple your upload speed with only 5MHz of bandwidth on band 8 as the primary carrier.

[MeltdownSpectre]

There are two possibilities I can think of:

1. The mast does not allow CA from data-only devices such as routers to conserve the narrow 5MHz band 8 for phones.  As band 8 can penetrate building material much easier than band 3, phones are more likely to use band 8 particularly in weaker signal areas.
   
2. The mast may require band 8 as the primary (upload) carrier for CA.  Below a certain RSRP (usually around -108dBm to -112dBm) on the higher frequency bands, the eNodeB will hand the device over to a low frequency band, so your phone is more likely using band 8 as its primary carrier.
   

Unfortunately there is no way to force CA, however, you can try cell locking your router to the band 8 cell to see whether it will aggregate band 3 with the following command.  First ensure the band selection is auto.  This command is based on the cell ID and earfcn from above:

/interface lte at-chat lte1 input="at+qnwlock=\"common/4g\",1,3748,136"

To remove the cell lock:

/interface lte at-chat lte1 input="at+qnwlock=\"common/4g\",0"

Some mobile networks don't tolerate cell locking to a low frequency band when high frequency bands are available above a certain signal level.  If this is the case the cell lock will cause the connection to cycle down and up as the network tries getting the modem off band 8.  However, even if this works, this will likely cripple your upload speed with only 5MHz of bandwidth on band 8 as the primary carrier.

Thanks for the explanation. For possibility #1, is it possible for the carrier to enforce this rule only in rural areas and on certain sites? 

Only asking because the router was happily doing CA in a different city.

I tried the command to force cell locking, and it worked for a few seconds, showing B8@5MHz as the primary band and B3@20MHz as the CA band, however the connection dropped before I could even start a speedtest and got stuck on 3G after that for some reason.

Removing the cell lock just made it go back to single band B3@20MHz. So far speeds still seem far better than the old Huawei B535-232 we were using here and the MikroTik doesn't require constant reboots like that did.

[Bonom]

Hello Seán and thank you so much for giving helping hands to so many people here!

I have an Mikrotik LTE18 ax too which I am going to make it 4x4 external antennas as it was very well described above.

My antennas are:
1. TRANS-DATA LTE MIMo 4g, 10dBi, with frequency range 698-2700 MHz (see picture 1)
2. Yagi MiMo 4G for rurals, 800-2600 MHz, 2x12dBi (see picture 2)

My location is rural and three of nearest towers are between 9 to 11 km (see picture 3 attached). Towers emit in 3 & 20 and 1 & 20 LTE bands.

Please help me with the best antenna position - at least in theory  - from the point of best carrier agregation and speed/bandwidth figures - I know I will need to try a lot of positions to find the best one.
Thank you very much and can't wait for your reply.


   

   

   

[Seán]

The two large antennas are log periodic like the Trans Data two, but with a higher gain due to the additional elements.  A Yagi antenna looks like an arrow and usually covers a single band only, e.g. 800 to 900MHz. 

Connect the two large +/-45 degree antennas to ANT2 and ANT3 and the Trans Data vertical/horizontal pair to ports ANT1 and ANT4 (from the U.FL to SMA pigtails mod).

I suggest testing each tower one at a time around peak time, such as between 8pm to 10pm.  For example, start by aiming the 4 at the lower-left tower and run some speed tests.  Repeat for the upper-left tower and upper-right tower.  Depending on the terrain, obstructions, etc. you may not be able to pick up all three towers.  Once you determine the tower that delivers the fastest speeds, you can find tune the antenna alignment in 5 to 10 degree increments to try getting the SINR reading as high as possible. 

(Correction - Removed antenna advice that does not apply to this the LTE18 ax model)

[Bonom]

Hello Seán and thank you for the answer,

I have only 4 ports for external antenna A1 to A4 as MeltdownSpectre showed in his pictures.
Do I understand correctly that I should find the best tower and to direct all antennas to that tower OR I could direct them to TWO towers like one pair to one tower and the other pair of antenna to another tower?

[Seán]

I mistakenly gave advice about the Chateau 5G ax model which has 8 modem ports internally. For the Chateau LTE 18 ax, connect the long antennas to the middle two ANT2+ANT3 ports and the Trans Data pair to the ANT1+ANT4 ports from the installed U.FL to SMA pigtails.

All four antennas should be aimed at a single tower, at least initially to see which provides the best speed. You can try aiming the Trans Data pair at another tower with the separate band to see if the network supports carrier aggregation between two separate tower sites, e.g. if the long pair is aimed at a B3+B20 site, try aiming the Trans Data pair at the B1+B20 site to see if it reports all three bands (B1, B3 and B20) as the Primary / CA bands. So far I have not seen carrier aggregation between two separate sites within Ireland apart from for 5G NSA, at least not with Three or Eir.

[Bonom]

Thank you very mych Sean, I appreciate your help

[Bonom]

Hello again Sean!

I am going to acquire a 13 metter height mast on which I would like to put those two pairs of antenna showed above.
My aim is to catch a tower situated 22 km away which emit mainly in B3 (1800 Mhz).  

Could you please recommend the best - best antenna configuration for this task, considering those two antenna pairs (2xYagi and 2xTrans Data)?

Also, based on cellmapper info regarding that tower, I understand that there are different antenna on that tower which emit in different directions.
How this (different antenna directions) can affect my purpose of acquiring 4g signal from that tower?

Thank you in advance!

   

[Seán]

Unless you are purchasing the mast primarily for Amateur Radio or another purpose, it would be a very risky purchase just to try picking up service from a distant 4G mast.  Compare the price involved to Starlink, which just needs clear view of the sky if it's available in your country.  For example, here in Ireland Starlink costs €349 for the kit and €50 per month for the service at this time of post.  The cost of purchasing and installing a tall lattice mast here in Ireland would pay for several years of Starlink be less susceptible to severe weather such as lightning surges, storms, etc.:

https://www.starlink.com/residential

Check also the line of sight between the GPS coordinates of the mast and your current location to see how high the obstructions are along the path.  If 13m does not provide clear line of sight, you could still end up with a very weak or no signal in that direction:

https://www.scadacore.com/tools/rf-path/...-of-sight/

The antenna configuration would be the same as I suggested above, i.e. connect the two large +/-45 degree antennas to ANT2 and ANT3 and the Trans Data vertical/horizontal pair to ports ANT1 and ANT4 from the U.FL to SMA pigtails mod.

The cellular mast antennas that face other directions (also know as sector antennas) can be an issue if you are directly in-between two sectors.  In this case, whichever sector your router connects to, the other sector will cause some interference.

[Bonom]

Hi Sean,

No, its a really cheap mast which costed me around 100 euro, I will send you more details tomorrow.

About antenna configuration...I wondered actually what would be the most suitable positioning including angles and distances between them?  It should be a romb or cross ...what it should look like?

[Seán]

The 4 antennas should be aimed directly at the tower. I suggest spacing the antennas in each pair at least 60cm apart.

For the spacing between the two pairs, you can try 100cm to 150cm to start with. Due to 4x4 MIMO's use of multipath propagation for the second MIMO pair, the optimal spacing will be different from one location to another, so I suggest try a few different spacings between the two pairs to see how it affects the speed. The main thing is to have the second pair aligned horizontally/vertically if the main two are aligned +/-45 degrees as this alone will provide at least 3dB separation between the two MIMO pairs.

[Bonom]

Good morning Sean,

Some details about the mast I spoked earlier, basically its a selfmade mast from steel tubes of different diameters just to fit one into another just like a telescopic tubes.
So there are 7 tubes in total,each of 2 metters, so we have 2.1 metters compacted (like in the picture bellow) and 13 metters in total when unfolded. 

   

The mast must be tied/fixed, and there could be lot of ways to fix it, like in this picture bellow

     

Ok, regarding the 4 antenna positioning, I understand the following:

1. The firs pair would be those 2 yagi placed 45 degrees and at least 60 cm one from another. 
 How should I place them? vertically like here       or horizontally like here      ?

2. The second pair (the trans data one) I will place them bellow the Yagies keeping a distance of at least 100 cm bellow them, correct?
These ones I understood that one shoulde be places vertically and the other horizontally. No big questions here.

3. I have a missunderstanding regarding one of your previous posts where you propose to use some different distances between antenna like 30 cm between pairs and 90 cm between antenna within pairs    

thank you again, and have a nice weekend Sean!