How to differentiate the transmission from the reception signal in a cellphone

Thread Starter

Titanpick

Joined Sep 9, 2017
16
Hi,

I would like to know how do cellphone differentiate the sent signal from the received signal. Does he use a different antenna for transmission than the antenna which he uses for reception ?

If it's like that, i would like to know if there are some phones which use the same antenna for transmission as the one they use for reception of the signal? If yes, in that case, how do they separate the transmission from the reception part?
Do they use some kind of a switch or chip for that?

Thank you
 

AnalogKid

Joined Aug 1, 2013
8,138
Working from memory of early phone systems that might no longer be true, one antenna that switches rapidly between transmitting and receiving.

ak
 

AlbertHall

Joined Jun 4, 2014
8,506
The ones I worked on used a directional coupler to separate the TX and RX signals but that was 15+ years ago. I don't know what they use now.
 
Hi,

I would like to know how do cellphone differentiate the sent signal from the received signal. Does he use a different antenna for transmission than the antenna which he uses for reception ?

If it's like that, i would like to know if there are some phones which use the same antenna for transmission as the one they use for reception of the signal? If yes, in that case, how do they separate the transmission from the reception part?
Do they use some kind of a switch or chip for that?

Thank you
I am not very expert but i think there is circuit called TX and RX inside the phone which means TX = Transmitter RX = Receiver. These two things do the specific job receiving and transmitting
 

k7elp60

Joined Nov 4, 2008
555
I am not very expert but i think there is circuit called TX and RX inside the phone which means TX = Transmitter RX = Receiver. These two things do the specific job receiving and transmitting
I do not know the frequencies of the current cell phones. I do know this that the transmit and receive frequencies are different. The same antenna can be used for both the transmitting and receiving frequencies. The difference is easily filtered. That is to say when talking the transmitter does not affect the receiver. The operation is generally known as full duplex operation.
 

AnalogKid

Joined Aug 1, 2013
8,138
I believe the transmit and receive RF frequencies are different.
Checked with an ex-ATT friend. For US CDMA, the transmit and receive carrier frequencies are different but close, like 200 kHz apart. On the tower they are two separate antennae. In the phone it is one antenna switched between the input and output stages, so the digital voice data is half-duplex.

ak
 
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