Antenna for LTE modem

I've recently bought a strongish directional antenna for my LTE modem,

and the cables to connect to the modem.

But when I connect it to my Sierra Wireless 7455 card (which is working fine with small omnidirectional antennas, connected to my OpenWrt router) the connection drops and it does not come back.

When I connect the same thing to my Huawei B310s-22 LTE modem (which is a full device with its own web interface and ethernet and wifi capabilities, it's not running OpenWrt of course) then it works correctly.

Another weird thing is that while this antenna claims it's MU-MIMO whenever I connect both cables the signal intensity drops dramatically, so I suspect that this "dual antenna" is just supposed to be used one at a time, depending on how the antenna is oriented (horizontally or vertically, as that's what is labeled on the connectors).

I might just saw the metal plate and make two separate antennas out of this thing later if I figure out why it's not workign with the Sierra Wireless modem card.

I'm suspecting that this antenna requires some signal booster circuit that is present in the Huawei full device but is not present in the Sierra Wireless M.2 card.

Since I'm a goat in this field and Google is failing me, does anyone know what is the problem?

Some modem can measure the signal strength with an additinoal pcb parts on the antenna and on the modem. Maybe the original antenna has this and the modem due a check? A PLS8e from does have this feature.

I doubt it, as the antennas it works with are the dumb, simple and cheap 2 dbi ones that look like the 2.4ghz wifi antennas.

The Sierra Wireless card I'm using is designed for laptops and other such devices (it's a Dell branded card that I reflashed to generic with ).

How do you know the cables are working? If I found the correct specs, then the antenna comes with N female and the B310s-22 with SMA female connectors. The EM7455 has MHF4 female connectors of course. So you must be using different sets of cables. And MHF4 to N is somewhat uncommon, and most likely handmade by someone... So how do you know they work?

The sierra modem is in a usb 3.0 metal enclosure like the one depicted in the link above, that has SMA-MHF4 tiny cables inside, see the images.
The modem loses connection as soon as I detach the 2dbi SMA antennas so I think this part is working fine.

I have bought a couple N-SMA cables (50 cm) and I'm using the same cables for both the B310s-22 and the Sierra modem.

which from the manufacturer specsheet
should be the right kind (50 ohms) for the antenna.

But maybe I've missed something obvious. As I said this isn't really my field.

Right, that makes sense. So you are actually using N to RP-SMA and RP-SMA to MHF4 cables for the EM7455, and both cables are tested. Then I have no clue what could be the problem.

So, just to confirm, I should be able to connect the Sierra Wireless 7455 card directly to any antenna rated for 50 ohm and it should work, right?

Because at this point I'm going to send back the current antenna as "not working as intended" and try with another one (a yagi maybe).

I am sure there are other restrictions than just impedance matching. There is a whole "Antenna Specification" appendix in the EM7455 Product Technical Specification. You have to match the gain of the two antennas for MIMO for example. And the two antennas should have more than 10dB isolation from each other. Etc. Etc.

It's probably also possible to overload the receiver, although I'm not certain you can do that with normal antenna gain. But this should be easy to test with an attenuator. Be aware that the EM7455 probably is designed for antenna systems with gain around 0dB (including cabling). Using a high gain antenna with short cables isn't necessarily a good thing....

so I suspect that this "dual antenna" is just supposed to be used one at a time, depending on how the antenna is oriented (horizontally or vertically, as that's what is labeled on the connectors).

no, that is for cross polarization which is, in your situation, probably a good thing. if you are using a directional antenna you need to aim it at your base station.

I know what "directional" means, I already pointed the antenna around in a full circle.

If both connectors are in use, I don't get any signal and no connection even on the Huawei modem-router.

I've already sent back the antenna as "defective" though, as it's not really working properly even with the Huawei modem-router, heck, it's getting better signal with its own internal (still directional) antennas.

I know it's a older thread, but I am. Having they very same issue yet with another ensemble:

  • Router Turris Omnia running v.5.1 (OpenWrt 19.07.x)
  • Quectel EP06 LTE-A modem (with spec telling 50 ohm impedance)
  • 3 generic wifi 2 dBi gain antennae with which I can get a stable connection
  • 3 DeLock 88808 high gain 9 dBi antennae (also 50 ohm impedance) with which attached Luci/network/interfaces shows network device is not present (for more details also see In first place I concatenated several adapters, but today I tried with a direct EP06-MHF↔ MHF-to-N-pigtail↔ N-antenna, and still got the error.

Long story short - which antennae did you buy that where working, @bobafetthotmail ?

None, since I don't feel like buying stuff blind, testing and sending it back multiple times.
I also got mildly pissed off at how OpenWrt interacts with modems so I ditched the Sierra Wireless card setup too. I strongly suspect that now that ModemManager is available in OpenWrt, using a modem should be less frustrating, but I never got around to try it out.

So I went with maximum jankiness solution using the Huawei modem's internal antennas, but it has worked so far.
I took the Huawei B310s-22 modem-router I had, I added a ghetto PoE adapter (it's using 2 wires of the ethernet to send power, so a gigabit cable becomes a 100mbit cable, not a problem since the modem itself can't do more than 100Mbit anyway and has a 100Mbit port), I threw the whole modem-router in a weatherproof enclosure and I mounted that thing on the roof, aimed towards a tower (aim was adjusted by trial and error, checking the signal meter on the modem's management webpage)

In the worst weather conditions (as apparently weather affects the signal) I can download at 15-ish Mbit and upload at around 5, and I can watch a youtube 1080p video without buffering, which is better than what I got with the Sierra Wireless card and its antennas, while also stable and I don't need to restart connection or reboot the whole router connected to the modem after it lost connection, which happened daily with the sierra wireless card setup (I don't blame the card, I'm in a rural place with poor coverage, sometimes the huawei modem loses connection too but it can re-connect on its own).

This setup has double NAT of course because the modem-router is between the main router and the Internet, but until I get a SIM contract with a static IP I don't really need to change this setup.

1 Like

Thanks, totally understand your frustration...
I maybe found the potential culprit - it seems some antennae (the technician whom I had an informative conversation with called them "external antennae" - this seems like an identifier for the modem which kind of antennae is connected) have a direct current grounding and there are some modem cards out there, that will shut down when "short-circuited" with such an antenna, as they are only designed to work with "internal" antennae.
I have yet to confirm my EP06 modem doesn't like DC grounded antennae by using a multimeter I just ordered today. But if yes, there's only a very small number of compatible antennae available on the consumer market :-1:

So here's the result of my researches: there are literally zero outdoor antennae available without DC-grounding. Maybe noname vendors might work, but I'm tired of trial am error.
So I need to search for another modem card unfortunately as my solar roof will prevent internal antennae from working properly :pleading_face:

I think your attacking this the wrong way.

Instead of using an indoor modem with a external antenna outdoors.

Try using an outdoor modem or an indoor modem installed outdoors in a weather proof enclosure and then run a ethernet cable or whatever indoors to your router.

Hm, I belive that is the right way to go - the modem card seems to not fulfill my requirements (which I couldn't have known beforehand as the manuel didn't show that information). I am not giving up hope that there is a modem card out there accepting outood antennae :slight_smile: