HELP: How to link multiply transmitter to one receiver

The following Question was posted on element-14.

Yu Jie Soh asked”  

       I would like to ask how can i link seven Transmitter to one receiver. I am using QFM-TX1-433 as my transmitter and QFM-RX1-433 as my receiver and also RF803E for the rf encoder, RF803D for the rf decoder. Currently I am able to link one transmitter to the receiver individually. It works perfectly when i operate one transmitter at one time, but when i operate more than one transmitter, the receiver can only able to detect one transmitter at most. I am just sending one digital signal. I had used the same input for the encoder but configured differently at the output of the decoder for every encoder. I would like ask is it I had used the wrong rf transmitter and receiver, or I had done wrong in the connection. The circuit is about the same as the one in the datasheet, just that I did not include the serial port, I just used all the outputs from the decoder.

Thanks alots in advance.

Chris Pinter responded: “

       This is a normal part of designing radio systems.  Most if not all radio systems have to deal with multiply transmitters. If you are having problems sending a signal from one transmitter to the receiver while the other six units are turned on it is likely that the transmitters are transmitting beckon packets without your knowledge.

       You will need to look at the firmware of the transmitter and receiver and develop a method of synchronizing the transmitters so they do not step on each other. Instead of developing the firmware yourself you might be able to get some help from the manufacturer of the radio modules.  They might have provided a patch or a method of synchronizing the transmitters within the development firmware.   I would give them a call first.

      If you need help with firmware design I would suggest you consider a simple multiplexing algorithm that incorporates Aloha protocol.  This will solve the next problem you will face, which is an increase in packet errors due to heavy traffic on the channel.

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