• Hello,

    I hope I'm typing this in the right place. I'm trying to build a 4 channel communication system using FM. The system should enable one person to initiate a call to three others and the channel should be duplex. That is the remaining three cannot make a call, only receive. Now, I have some idea but as this is my first serious and involving project I can't organize my ideas.

    What I have in mind is:

    (1) I first create my base frequency using a Colpitt oscillator and get the frequency I want which is about 10 MHz (suitable for my oscilloscope).

    (2) Then I have to shift this frequency by about 200Khz to provide the necessary channels to communicate with the others separately.

    (3) Then since the controlling station has to choose who to communicate with, he has to have some sort of a switch which can pressed to allow the frequency corresponding to one of the remaining three channels to modulate his audio frequency. That can be done using an analog knob or an encoder with a multiplexer.
    (4) The frequency which has be chosen then gets into an FM modulator which it is encoded with the audio signal

    (5) Then transmit.

    (6) The receiving end gets some notification when a call has been initiated.

    (7) The receiving end needs to have a transceiver which has a receiver operates at the downlink frequency and a transmitter which operates at the uplink frequency

    I guess that is all. I’m not yet an engineer and really have a limited practical knowledge and I hope someone with experience in the telecomm field can tell me if my ideas are in the right plane. What I’m afraid of is the transition from theory to practical because things which tend to work on paper don’t necessary work in reality like you can easily calculate the necessary RC values in a Phase Shift Oscillator to make it work in the high frequency band and in reality has a max bandwidth of 1MHz.
    I hope someone can help me.
    Thank you.
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  • fissss

    MemberAug 13, 2011

    I am a 4th year student in communication systems engineering, i don't promise i can sure help you, but i have the same trend like you in achieving a communication system as a graduation project, so i think we can help each other by exchanging information in this field, I have passed before many courses related to mobile communication (GSM and UMTS).

    so would you mind to give me any contact number or email for you?

    Mohamed Saad
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