RF transmitter not working when a second one is turned on

Discussion in 'Wireless & RF Design' started by gvandenbosch, Apr 27, 2014.

  1. gvandenbosch

    Thread Starter New Member

    Aug 1, 2013

    I have made a PCB with a 433MHz RF transmit module.
    The module I am using is the T7G-434-075 from RF solutions.
    Datasheet: http://www.rfsolutions.co.uk/acatalog/DS307-7.pdf

    When only one PCB is turned on this is working perfectly.
    A message is transmitted on a trigger by activating an optic sensor.

    When I turn on a second PCB, only one of the PCB messages are received when the sensor is triggered.

    When I turn of the PCB that the messages are received from then when activating the sensor on the second PCB the messages are received which was not working when the other PCB was turned on.

    They don't transmit continuously only when it is triggered. So I have no clue why the messages are not received from one PCB when a second one is turned on and the second one is not sending.

    I have attached my schematic of the PCB.
    A change I made which is not on schematic is that I have soldered a 100nF capacitor between VCC and GND on the antenna but it didn't help.

    Could anyone give me a pointer on what else I could try or what it could be that causes the behavior?
  2. bertus


    Apr 5, 2008

    Looking at your schematic, the transmitter is always on.
    When two transmitters are transmitting on the same frequency, they will interfere.
    The power of the transmitters is not switched.
    When switching the power, please mind the power on time to stabelize.

  3. gvandenbosch

    Thread Starter New Member

    Aug 1, 2013
    Hi Bertus,

    Thanks for the pointer, this has solved it.

    I used a transistor now to switch on the transmitter from the microcontroller before I send and disable it after sending. It is working well now.