Hello all,

I've got very little knowledge on complex electronics so looking for any advice on installing a small retrofit project to my car. I plan to fit a 4g mimo roof antenna (a oem bmw shark fin with 2 built in antennas in one unit) with internal compensator (small amp) linked to an internal repeater antenna. The 4g mimo antenna came from a car with a SIM card subscription based telematics module, for sos calls, link to the car dealership and mobile Internet for the cars media system etc. I am wanting a simplified version with no telematics module. What I'd like to understand is, if I connect the 2 x 4g phone outlets on the antenna together to from a single cable to connect to the amp, will it work without the electronics of the telematics module? Since mimo uses 2 antennas for receiving and one for sending, I'll be using 2 for sending as I won't have the complex module to seperate the sending signal to one antenna.
My present 3g antenna is wired straight to a internal repeater.

Thanks
Alan

 

Photos

 

You can't just connect the two antennas together. You might be able to use one of them.
In theory you could connect the two with a properly made phasing harness but it's not worth the trouble.

 

You can't just connect the two antennas together. You might be able to use one of them.
In theory you could connect the two with a properly made phasing harness but it's not worth the trouble.

Thanks for reply.
So the telematics module would have to be fitted for this antenna to work as a mimo?
Is there no generic modules that can perform the same task?

 

Thanks for reply.
So the telematics module would have to be fitted for this antenna to work as a mimo?
Is there no generic modules that can perform the same task?

It's a very specialized device. If you are not connecting it to something that understands the MIMO hardware it is unlikely you could really get any benefit from it. It's a system and the antennas are just a part.

 

It's a very specialized device. If you are not connecting it to something that understands the MIMO hardware it is unlikely you could really get any benefit from it. It's a system and the antennas are just a part.

These types of mimo shark fin antennas with built in GPS and DAB are sold by other companies as a stand alone devices, everything contained within the unit. I wonder what they use to switch from double antennas to single?
https://www.linkwave.co.uk/shark-fin-antenna

 

The telematics unit shown in the photo is labelled '4G MIMO GNSS ...' so presumably is a MIMO capable device. As a MIMO device it will have two antenna ports and they both need to be connected to separate antennas - presumably the BMW Shark-fin was designed specifically for this purpose. There should also be an antenna for the GNSS (GPS) function. You say you will be using 2 (antennas ?) for sending. I think this is unlikely; almost all LTE (4G) devices have only one transmitter and it will be duplexed with the primary receiver antenna.

One other point; you say you will use a small compensating amplifier; I don't understand this; Is this a receiver amplifier? So how does the transmitter get past it to get to the antenna? Also, for MIMO to work properly the gain for the Primary and Secondary receivers needs to be more-or-less the same.

 

These types of mimo shark fin antennas with built in GPS and DAB are sold by other companies as a stand alone devices, everything contained within the unit. I wonder what they use to switch from double antennas to single?
https://www.linkwave.co.uk/shark-fin-antenna

That device just provides antennas, there are cables to every antenna in it. See the drawing. What you do with the antennas is up to you. It doesn't manage them in any way.

 

The telematics unit shown in the photo is labelled '4G MIMO GNSS ...' so presumably is a MIMO capable device. As a MIMO device it will have two antenna ports and they both need to be connected to separate antennas - presumably the BMW Shark-fin was designed specifically for this purpose. There should also be an antenna for the GNSS (GPS) function. You say you will be using 2 (antennas ?) for sending. I think this is unlikely; almost all LTE (4G) devices have only one transmitter and it will be duplexed with the primary receiver antenna.

One other point; you say you will use a small compensating amplifier; I don't understand this; Is this a receiver amplifier? So how does the transmitter get past it to get to the antenna? Also, for MIMO to work properly the gain for the Primary and Secondary receivers needs to be more-or-less the same.

The 4G GNSS DAB unit in the photo is the shark fin, not the telematics module that I do not have, or want. There is 4 outlets on the shark fin, 2 for phones, 1 for gnss and 1 for dab. The compensator is just a small amp and used in conjunction with the shark fin antenna. A coaxial cable from the amp goes straight to a repeater antenna so the mobile phone is not always on full power searching for a signal due to being inside the car. The shark fin unit contains 2 x 4g antennas and can be seen in the form of stick on thin copper on the shark fin casing. What I don't know is, does the antenna unit switch from 2 antennas to 1 or is it the telematics module that carrys out this action, or does it even matter if 2 are connected for transmitting?
Maybe the telematics module is needed as you say as it will have two seperate inputs for 4g from the shark fin. I thought the shark fin may have been a stand alone unit and could connect almost directly to a smart phone via an amp while still having functional mimo 4g signal. The compensator must allow transmitting and recieving as one port is connected to the phone and the other to the telematics module then shark fin. Its the way bmw designed it, how it works is anyone's guess.

 

The MIMO function is performed in the transceiver, both the shark fin you have and the one you showed me are just antennas.

 

The MIMO function is performed in the transceiver, both the shark fin you have and the one you showed me are just antennas.

Maybe a stupid question, is the mobile phone not the transceiver?

 

Maybe a stupid question, is the mobile phone not the transceiver?

The mobile phone is a transceiver, but it is not the transceiver that connects to the several antennas provided by the shark fin. The repeater is that transceiver, and unless it has multiple antenna ports, you can't use multiple antennas with it.