Differences between dBi antenna strengths?

King Mustard · 7 Jun 2018 at 14:11

I have a Huawei E3372h-153 4G USB dongle.

I believe it uses CRC9 connectors for the external antenna connections.

When searching for "CRC9 4G antenna" on eBay, results seem to show 12dBi, 2.5dBi, 5dBi etc.

When looking for an external antenna, which dBi should I be looking for?

What's the differences?

PaulCa · 7 Jun 2018 at 14:34

Certainly in patch antennas higher dB usually means higher gain and a tighter 'beam' pattern, so longer range but receives over a smaller target area.

If you know where the cell mast is and are comfortable aiming the antenna precisely then go for higher gain.

King Mustard · 7 Jun 2018 at 14:46

The dongle will be in my Android car stereo, so it'll be hopping between cell towers constantly.

PaulCa · 7 Jun 2018 at 16:14

Then if my understanding you do not want a panel/patch type antenna but an omni directional "rubber duck" antenna like a normal wifi router. The gain does something to the shape of the toroidal pattern on them, but it's been too long since I did any RF antennas to remember.
https://en.wikipedia.org/wiki/Rubber_ducky_antenna

King Mustard · 7 Jun 2018 at 16:16

Is this a bad idea?

PaulCa · 7 Jun 2018 at 16:16

Also placing the antenna inside the car will cause issues with reflections and blocking. It would ideal to have the antenna outside the car.

PaulCa · 7 Jun 2018 at 16:18

King Mustard said:
Is this a bad idea?

Yes. High gain flat (patch) antennae are highly directional. You have to point them at the other station. These are great for 4G broadband connections for a fixed location with a mast several miles away.

King Mustard · 7 Jun 2018 at 16:20

PaulCa said:
Yes. High gain flat (patch) antennae are highly directional. You have to point them at the other station. These are great for 4G broadband connections for a fixed location with a mast several miles away.

Which would you recommend?

PaulCa · 7 Jun 2018 at 16:23

This looks like a good Omni-directional antenna.
https://www.ebay.co.uk/itm/UMTS-ant...586525?hash=item3d561a905d:g:IcMAAOSwax5Yy7wU

My experience is with 2.4Ghz video from a drone where we used a high gain patch (15dB) antenna on the ground and a rubber duck omni on the plane (3dB).

King Mustard · 7 Jun 2018 at 16:24

PaulCa said:
This looks like a good Omni-directional antenna.
https://www.ebay.co.uk/itm/UMTS-ant...586525?hash=item3d561a905d:g:IcMAAOSwax5Yy7wU

My experience is with 2.4Ghz video from a drone where we used a high gain patch (15dB) antenna on the ground and a rubber duck omni on the plane (3dB).

The thing will be in my glove box (where the dongle is). Will that cause issues?

I'd rather not have it on display, in fear of people breaking in.

PaulCa · 7 Jun 2018 at 16:28

It will lower your range. But most mobile phones have terrible range anyway with a tiny internal antenna. You will probably get something similar to a mobile. As a worse case you can always stick the antenna to the window when in the car with a suction cup.

King Mustard · 7 Jun 2018 at 16:28

PaulCa said:
It will lower your range. But most mobile phones have terrible range anyway with a tiny internal antenna. You will probably get something similar to a mobile. As a worse case you can always stick the antenna to the window when in the car with a suction cup.

Thank you a lot for your help!

PaulCa · 7 Jun 2018 at 16:34

I would recommend using a signal monitor app and playing with the orientation of the antenna to work out if it works best horizontally or vertically. I did a quick google but couldn't find anything quickly on UMTS polarization.

Caged · 7 Jun 2018 at 20:10

If you're shoving it in the glovebox then why even bother putting an external antenna on

King Mustard · 11 Jun 2018 at 19:47

Caged said:
If you're shoving it in the glovebox then why even bother putting an external antenna on

I was hoping there would be some kind of cabled solution that I could have coming out and toward the bottom of the windscreen.

Steveocee · 12 Jun 2018 at 10:16

If you are going to be roaming around then whilst a higher gain antenna seems common sense it's actually not.

Like anything there is no such thing as a free lunch, a "true" 0 gain omni antenna will propagate in a full sphere, once you begin to add gain to your antenna you effectively start taking chunks out of your receive coverage area (horizontal or vertical or both). so whilst a 10dB antenna sounds so much better, that 10dB is only stronger in a % area of what an omni receives in.

The best analogy I can think of is the light output pattern of a bulb on its own (full spherical) to that of a lighthouse (tighter ray but stronger where it does go).

So whilst your antenna if pointing in the right direction can potentially give significantly better signal, if it's in the wrong direction will give significantly worse performance than a built in omni.