Transmitter modules in same frequency

Discussion in 'Wireless & RF Design' started by Bilnigma, Mar 17, 2008.

  1. Bilnigma

    Thread Starter Member

    Mar 10, 2008
    11
    0
    i am currently on a project involving several transmitters sending signals to a single reciever. i am using a encoder decoder pair like MC145026D at the transmitters and reciever respectively. i am using HX1000 and RX1000 as transmitter and reciever modules respectively. HX1000 recieves a serial inupt and RX100 outputs a serial data.

    Question: if i use the transmitter(HX1000 or any) to CONTINUOUSLY send a signal from each transmitter (all transmitters will be operating at same frequency), will the reciver be able to recieve all the signals at its output or will the signals be corrupted beyond recognition.

    can u suggest any modules that can operate at same frequency and be uncorrupted at the receiver.

    ur suggestions r appreciated, thank u
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    "Corrupted beyond recognition" about covers it. About the only way to manage multiple xmitters into a single receiver without handshakes is to establish a common timebase and only allow each xmitter to send data during its alloted period. That is called a round robin transmit scheme.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Instead of a single receiver and many transmitters, you might consider having transmitter/receiver pairs at each location. One is designated the master, and has a microcontroller that issues "requests" for data from the other stations.

    The master issues a fixed length code identifying itself, and a subsequent fixed-length code identifying the unit from which the data is requested, and (optionally) the type of data to submit; whether "changes only", a specific type of data, or all data waiting to be transmitted.

    The slave units are constantly listening, and only respond when they are directly addressed by the master.

    By having the slaves report "changes only", you can save a lot of bandwidth. But that may not be appropriate if there's been a power or communications glitch that needs to be recovered from.

    You'll also need routines to handle situations where a slave doesn't answer; perhaps re-try a few times, then set an error message and only retry intermittently to re-establish a link.
     
  4. Bilnigma

    Thread Starter Member

    Mar 10, 2008
    11
    0
    thanks for the suggestions :)
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    Would it help if the Master transmitter operated at say 915MHz and all of the slave receivers operated at 915MHz. Then all of the slave transmitters would operate at say 433MHz and the Master receiver would operate at 433MHz.

    With this arrangement there would be no chance for the outgoing data from the master to interfere with the incoming response from the addressed slave.

    hgmjr
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    I can't see offhand how that would help - but you would be tying up two frequencies instead of one ;)

    If the master unit was busy sending out requests for data, it may not have time to monitor the receiver. The premise I was going on was to keep the station ID's and data requests very brief, to conserve power. Transmitters usually consume more power than do receivers, unless perhaps they're micropower transmitters.

    Of course, if one transmitter got "stuck" transmitting, the entire system would be jammed up. :p
     
  7. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Sounds like the remotes would only transmit after being polled by the master. That should keep the channel clear. A lot of addressable fire alarm systems work this way. (Albeit over wire rather than RF.)
     
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