Differences between dBi antenna strengths?

[Elliot B.]

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?

[+Biscuits Brown MVC]

That is a measure of antenna gain. Generally the higher the better. If you physically have room for and can find one that has your connector, I'd select the one with the  highest gain - assuming you know that signal strength is an issue and that a high gain antenna will address it.  If you do not have a signal issue, too much gain can actually cause problems. I'd buy something in the 5-12dBi range and test it. Avoid the really high gain items (24dBi stuff).  Only go with as much gain as you need.  

[Elliot B.]

24 minutes ago, Zag L. said:

That is a measure of antenna gain. Generally the higher the better. If you physically have room for and can find one that has your connector, I'd select the one with the  highest gain - assuming you know that signal strength is an issue and that a high gain antenna will address it.  If you do not have a signal issue, too much gain can actually cause problems. I'd buy something in the 5-12dBi range and test it. Avoid the really high gain items (24dBi stuff).  Only go with as much gain as you need.  

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

[+Biscuits Brown MVC]

So your car has an Android system that has no 4G connectivity but  you have added the dongle to get connected. Does the dongle NEED an external antenna or can is work without?  

[Elliot B.]

1 minute ago, Zag L. said:

So your car has an Android system that has no 4G connectivity but  you have added the dongle to get connected. Does the dongle NEED an external antenna or can is work without?  

The dongle itself has an internal antenna (as they all do) but it's not very good.

[Astra.Xtreme]

A high gain antenna is beneficial when you know the direction the signal is coming from, which you can then focus the antenna on.

For something like a cellular connection where the signal will be coming from any direction, it's best to get a lower gain antenna to keep the connection width more spread out and thus more reliable.  2.5dBi is a good option.  5 is pushing it, and 12 I'd steer well away from.

 

[Elliot B.]

30 minutes ago, Astra.Xtreme said:

A high gain antenna is beneficial when you know the direction the signal is coming from, which you can then focus the antenna on.

For something like a cellular connection where the signal will be coming from any direction, it's best to get a lower gain antenna to keep the connection width more spread out and thus more reliable.  2.5dBi is a good option.  5 is pushing it, and 12 I'd steer well away from.

 

So you think this is a bad idea?

[sc302 Veteran]

1 hour ago, Astra.Xtreme said:

A high gain antenna is beneficial when you know the direction the signal is coming from, which you can then focus the antenna on.

For something like a cellular connection where the signal will be coming from any direction, it's best to get a lower gain antenna to keep the connection width more spread out and thus more reliable.  2.5dBi is a good option.  5 is pushing it, and 12 I'd steer well away from.

 

I think you aren't 100% correct here as it truly depends.  High gain antennas are omni directional, there is nothing to focus, they do however need to be up high to be able to receive weaker signals.  There are a lot of factors that come into play where db is just a small part of it. 

 

https://www.ubersignal.com/blog/antenna-amplifier-gain/

 

Quote

In summary: the gain of an amplifier represents how much the amplifier can enhance the strength of the signal. The greater the gain of the amplifier, the weaker the signal you can receive and still turn it into an acceptably strong one.

Likewise, the gain of an antenna represents how well the antenna converts radio waves into electrical signal or vice versa, depending on whether it’s receiving or transmitting.

As a rule, high-gain devices are generally higher-end products, specifically designed and optimized to boost signal strength by large amounts. When looking into purchasing a signal boosting system, it’s helpful to do a site survey to find out what combination of antenna and amplifier would be appropriate to boost your signal to an acceptable level in the place where you need it.

According to them higher gain is better for weaker signals.  

 

These guys seem to also agree

https://www.telstra.com.au/coverage-networks/network-coverage-extension-devices

Quote

 

Low Gain (0-2.5dBi) antennas are ultra-portable and designed to boost signal strength in good coverage areas. They transmit equally in all directions including vertically, making them ideal for built up metropolitan areas and regional centres.

 

Medium Gain (3-5dBi) antennas boost signal strength for voice and data devices within buildings, and in fringe coverage areas of the network. They focus the signal towards the horizon and are ideal for areas where the terrain is moderately hilly and base stations are further apart.

 

High Gain Antennas

These powerful 5-9dBi rated antennas can significantly boost the signal range for cars, homes and businesses in remote areas with patchy reception or nearby reception. High gain antennas are omni-directional and need to be mounted on the outside of your vehicle or building. They are ideal for flat or moderately hilly country where base stations are sparse, and for boosting coverage along major highways. They are not suitable if there’s no reception at all in the vicinity.

 

If you are weak due to location/bad placement/internal antenna sucks, then sure you can purchase a low gain antenna to receive signal.  However if you are in a truly weak area you will want a high gain antenna to be able to support your need, but it has to be mounted quite high...possibly more elevated than your vehicle will allow it to be.

 

Even your site where you posted that picture from states what/where and different scenarios where high gain antennas would be good and where low gains would be bad.  But they don't go into moving targets like cars.

For you reading pleasure: http://www.jpole-antenna.com/2014/03/28/antenna-gain-explained/

 

Disclosure: I don't claim that I have any knowledge of any of this.  Read for yourself/decide for yourself.

 

[Astra.Xtreme]

5 minutes ago, Elliot B. said:

So you think this is a bad idea?

Haha, yikes.  I would question any no-name antenna coming out of China, not to mention being it being a crazy 28dBi of gain.  There's an art to antenna design, and a cheapo one has a high chance of being a headache piece of junk.

You'll also need to consider how much power can be supplied to the antenna.  That Ebay one being 10W means that at 5V (just guessing what the source voltage may be), it needs to pull 2A, which may be more than the device can supply.  Overexerting the supply or under-powering the antenna will have negative effects.

[Astra.Xtreme]

40 minutes ago, sc302 said:

I think you aren't 100% correct here as it truly depends.  High gain antennas are omni directional, there is nothing to focus, they do however need to be up high to be able to receive weaker signals.  There are a lot of factors that come into play where db is just a small part of it. 

 

https://www.ubersignal.com/blog/antenna-amplifier-gain/

There's always some sort of focusing zone with any antenna, whether directional or omni directional.  Per physics of an antenna, there are significant dead zones, which is why positioning the angle of the antenna is critical.  Adding gain to an antenna increases the coverage zone, but also increases the magnitude of the deadzones.

That's why the concept of gain is more than just a number and has to be chosen properly for best performance.

 

[sc302 Veteran]

There is, and my experience is that omni is more of a dome than a bubble and directional is more of the picture you linked above and the signal is more focused and can usually travel farther than omni.  You are correct, the right antenna should be chosen for the best possible performance.  Where your suggestion of a low gain antenna could probably work if there is enough cell signal coverage in the area...which may be in question if the built in antenna can't pick it up.