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I am not that much familiar with communication and antennas.

I want to build a gsm repeater (gsm signal booster), but I am not sure if it works if I do it like the way we do for a radio. What I am trying to ask is that every signal in the air will br amplified if I build a simple system with one receiving and one transmitting antenna. Can my phone still distuingish the signal it uses?

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I am going to assume you already know how to setup the repeater/antennas, and know whether or not you need/will use an amplifier between the antennas. So I will just answer the question you asked:

If you have a working gsm repeater with no smarts on it (to boost only the signal your phone uses) then - Yes, it will amplify all signals, not just the one your cell phone uses. Your phone should still be able to pick out the signal it needs though.

The link tomnexus supplied in comments does have some good info on whether or not you'll need an amplifier in your repeater. Without more information on your planned setup can't say much more about it mate.

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  • \$\begingroup\$ So, if I amplify all the signals in the air, it will not be a very bad practice, after all. Is that right? \$\endgroup\$ – Zgrkpnr__ Jan 22 '15 at 9:36
  • \$\begingroup\$ It would work better to get a carrier specific repeater, one that will only amplify the frequency your cell carrier uses, but most people just boost everything. It's not a bad practice, no. It can introduce interference though, so some countries have regulations on how high a gain you can amplify the signal with (FCC in the US has a gain cap for non-carrier-specific repeaters). Not that you need to follow the regulations. \$\endgroup\$ – I. Wolfe Jan 22 '15 at 14:14
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Your question is confused a little confusingly, which doesn't help. But in general, a cell phone repeater needs to be designed quite differently to a radio amplifier. A cell phone doesn't just receive signal like a radio; it also communicates back to the cell phone tower.

As a result, amplifying signal in just one direction isn't very helpful: your cell phone won't work better if you have much stronger downlink without a correspondingly stronger uplink signal. Fortunately in most cases the uplink and downlink signals are split onto different frequency bands, making this slightly simpler (in contract, TDMA systems such as WiMax use different time-slots to communicate).

So you'd need to design a bi-directional amplifier with band filters that separate the uplink and downlink frequencies. Berthold Horn at MIT has a great series of articles explaining cell phone repeater basics. To get a sense of the complexity of some of these systems, you might try purchasing a unit from a cellular repeater distributor and checking the specific RF filters used to separate the uplink and downlink frequency bands.

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