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Active antenna amplifies received signals with active components, so it has better parameters. Active antenna for the only receiving systems like GPS and TV signals are exist on the shelves. But the active antenna for two way communication systems like GSM/GPRS devices are rarely or even non exist. It seems designing such these antennas are possible with separate parts for receiving and transmitting, but practically does it exist any active antennas for GSM communication?

I need to improve GSM/GPRS signaling for a M2M system in poor signal quality environment, so I need some recommendation for this purpose.

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closed as off-topic by Andy aka, brhans, Dave Tweed Jun 10 at 14:06

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"Active antennas" include an amplifier to improve reception.

This works well with things that only receive. GPS receivers and television receivers only receive. It is fairly easy to include an amplifier to make reception better.

GSM has to transmit as well as receive. It is much more difficult to make an active antenna if you have to be able to transmit through it.

If the communication schemes were simplex (either transmit or receive but never both at the same time) then you could include an automatic switch in the active antenna to disconnect the receiver amplifier when transmitting.

Phones aren't simple, nor do they use simplex communication. They transmit and receive at the same time.

Anything that can seperate the receive and transmit signals is already half of a phone.

Given that, there's not much point in having an active antenna. Your phone still has to split things to transmit and receive, so you might as well put any gain there (on the phone PCB) instead of the antenna. That keeps the antenna simple and cheap.


As to solving the actual problem:

There might not be much you can do.

You could use an antenna with gain. These are directional antennas that receive and transmit in one direction better than in other directions - the worse it receives to the back side, the better it receives to the front side.

The problem there is that consumer devices are limited in the amount of power they are allowed to transmit. A directional antenna can take you over the limit in its main direction. The power the phone transmitter sends stays the same, but it is focused in one direction. Kind of like you can look at brightly lit wall, but a focusing mirror of the same size in the same light would be blinding.

See if an omnidirectional antenna with gain helps. These get their gain by being taller than normal. They have poorer reception upwards, but better reception from all directions around them. Kind of like a donut shape.

Something like this:

enter image description here

Mount it in the center of a large, flat piece of sheet steel. Say, a square or circle about 1 meter across. Mount the whole thing outside the building, and on top (up high.) You'll need to see about proper grounding and lightning protection - if you don't, you can expect a lighting strike to take your system out of operation if the safety inspectors don't.

(BTW: That's probably not the right antenna. It is just an example. It probably has the wrong connector, and probably isn't in the correct band.)

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What you are looking for is properly termed a 'GSM Repeater' and there are many on the market.

These tend to be on the expensive side, and they may or may not be legal in your country. So, I would first check that a passive 'gain antenna' will not serve your purposes. Omnidirectional antennas are easily available up to 7dBi, and even higher gain is available if you can use a directional antenna in your system.

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  • \$\begingroup\$ "Active antennas" are parts that go in device, or are used with a device. They have a built in amplifier to provide better reception. That is a different thing than your GSM repeater, which is a standalone device. \$\endgroup\$ – JRE Jun 10 at 9:43
  • \$\begingroup\$ They can be stand alone, I've seen some with an RF connection for the local terminal equipment. They are too expensive for our applications; we use gain antennas, or another signalling method, for poor signal areas. \$\endgroup\$ – Cursorkeys Jun 10 at 10:05

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