Basic question on Cordless phones.

Discussion in 'Wireless & RF Design' started by Nathan Hale, May 5, 2013.

  1. Nathan Hale

    Thread Starter Active Member

    Oct 28, 2011
    125
    2
    Hi everyone, I was wondering there are a lot of cordless phones that operate on 900mhz frequency. If that is the case shouldn't ALL the people using these cordless phones have their conversations heard by everyone? What exactly stops my neighbor from picking up my cordless phone conversation even though we both have the same ( 900 MHz) freq phone?

    Thank you for all the replies.
     
  2. absf

    Senior Member

    Dec 29, 2010
    1,493
    372
    Modern mobile phones use digital technologies extensively. Though the Base Band may be 900MHz, each speech channel only occupies 64 Kbs on a 30+2 channel 2Mb stream. In the US the above might be different. On modern digital phones, your speech is immediately converted to digital form before it is transmitted to the RBS (Radio Base Station). The Mobile exchange would allocate your speech with a free channel available. The signalling might not be on the same channel with your speech channel.

    During the 80's, when we were using the 450 MHz analog technologies. It was called ATUR (Automatic Telephone using Radio) here. At that time one can buy a receiver which would be able to listen to the speech of conversations as well as the caller and called parties phone numbers and its coded IDs. But that was history now.

    Think of your phone as a FM radio with an automatic tunning. In a FM radio, you have to tune to the stations you're interested. But in the phone, the tuner is controlled by micro-processor which in turn is controlled by the Mobile Exchange for allocating the channels. You have no control on which channel you wanted to transmit or receive. So there is no chance for you to over-hear what others' are talking.

    As I am not working in the Mobile branch of my phone company, I dont know what are their latest developments. May be it has advanced so much that what I was talking is already out of date.

    Allen
     
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  3. circuitfella11

    Member

    May 10, 2013
    56
    5
    hi,

    it's not out of date absf.. they only added more allocated frequencies..

    it is really rare or not at all that you can arrive at the same frequency because of the frequency range, and of course, DSS(digital spread spectrum).. originally this was made to maintain privacy and integrity of calls..
     
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