This may help.
The voltage specs for these Transmitters and Receivers are a bit confusing.
The Transmitter will work with any voltage between 3V and 12V , but the Receiver needs 5V, and it needs to be
very close to 5V, otherwise the receiver wont decode properly, and this can show up as poor sensitivity / poor range.
Running the receiver off anything much above 5 V will damage it.