Car aerial 3g to 4g

[Alan]

Hello,

Great info on this site, best I've found for my application.

I live in a hilly rural area on the west coast Scotland where my phone is always on full power searching for or boosting the signal.
I'm looking to upgrade my car aerial system and while I'm at it, convert to 4g.
I'm not just looking for a better signal but also to cut down on the increased radiation within my car from the phone being on constant high power, exacerbated by being inside the metal car body.

Currently my aerial is a multi functional 3g GPS/ DAB/ 2xTEL OEM "shark fin" roof aerial, see below.     
I intend to change it for a later OEM multi functional 4g MIMO aerial, see below.           
The MIMO has different connections to the old 3g aerial. You can get a LTE aerial with the old connector types, see below           
However I thought fitting the 4g MIMO would be a worthwhile upgrade despite the need to change cables to fit?

The car had a standard outdated 3g SIM telematics box which I assume boosted the phone signal which I've already removed as I no longer needed its "connected to dealership services" and am going to replace with a 4g bands 1,3,5,7,8,20 booster such as a Cel-Fi go M with short range internal passive aerial. (unless someone recommends something better?)

I am struggling by 1/ Not being very knowledgeable on the subject and 2/ Not being able to find any clear info on the subject or BMW OEM wiring schematics.


The current 3g aerial has 2 outlets for phones, why I'm not sure as I dont think theres another diversity aerial, although the car does use a diversity aerial for the DAB, which also seems to act as the sole aerial for AM/FM radio reception, encased in the rear plastic spoiler.

The new OEM MIMO aerial I intend to fit, seems not to be linked to any other aerial either, determined by looking at very vague BMW parts images, yet it also has 2 phone outlets. 

Any ideas why the aerials have 2 outlets if no diversity aerial? maybe it does but self contained within a single unit?

Any advice or pointers welcome.

Thanks

Alan

[Seán]

Unfortunately, I've never dealt with car cellular antennas, let alone seen one until your post. The only in-car mobile phone signal booster I'm aware of is this kit made by StellaDoradus. This consists of an outdoor roof-top antenna, a repeater and a phone cradle that provides the signal directly to the phone, so when the phone transmits, the signal is fed directly through the repeater unit.

What I can confirm is that cellular 3G and 4G will both work with a single antenna. In fact, cellular repeaters that boost in-home phone 2G/3G/4G coverage work on just a single outdoor antenna.

With 3G, the second cellular antenna is for receive diversity, i.e. the cellular radio will attempt to decode signals on both antennas, giving a higher chance of usable data. It only transmits on one antenna.

With 4G, the two antenna are cross-polarised where one antenna picks up signals 90 degrees out of phase of the other antenna. This is known as 2x2 MIMO, which effectively doubles the throughput for the same amount of spectrum. 4G will work with a single antenna, but with about half the throughput of a 2x2 MIMO system. As with 3G, 4G only transmits on one antenna.

It is quite possible that the 4G MIMO shark fin antenna is intended for newer cars that have a 4G modem built-in into the car to provide in-car Wi-Fi. This is like the 3G telematics box you describe, but where you pay the dealership for hotspot access. A good example is Opel's OnStar Wi-Fi. Unfortunately, this type of system doesn't do anything to improve the signal on your phone other than provide W-Fi access.

[Alan]

Thanks for the info. That makes sense about 2 aerials for receiving and 1 for transmitting, maybe the shark fins have 2 aerials cross polarised built into them.
There is little to no info on the aerial schematic BMW use and I'm sworn to remove my headliner to trace cables from the aerial and modules until I am ready to the job.
I find the Shark fins quite a neat little package considering all that they do, aftermarket companies like panorama antennas sell them for £500+ 

https://www.panorama-antennas.com/site/G...Mo-Antenna

Edit, BMWs connected drive is a subscription based internet service received to the vehicle head unit, which is basically just like a smart phone with apps. The head unit transmits wifi to other devices in the car, or by bluetooth.