RF transmitter not working when a second one is turned on

Hi,

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?

I do not see the cause, but your RECEIVER may be confused if one or both transmitters operate at the same time.
Do you use a common power supply (battery) for both transmitters? Some coupling may occur.

They are running from separate battery.

The current thing I am trying is to use a transistor to switch the VCC of the transmitter.
When start sending then I turn the transmitter on from the microcontroller and turn it off when done.
Because it seems like to give noise when it is turned on but not sending.

According to the schematic, the transmitter is permanently sending and can't be turned off by the microcontroller. In so far it can be expected that two transmitters won't operate correctly when powered simultaneously.

Review the HT12E datasheet about usual means to disable the transmitter.

The HT12E has an enable/disable pin for transmitting but even when this was disabled it was blocking the other transmitter.

I solved it now by changing PCB with the transistor, before I send I enable the VCC to the RF and after sending turn it off, it is working now.