I am using some "no-name" (in fact "XY-MK-5V" stands on the board) 433 MHz receiver (and transmitter) on an Arduino project. I can receive the signals sent from my other Arduino very good (it sends with 12 V as mentioned in another question).
The problem is: I want to receive signals from other parts – such as simple power outlets wireless switches, too. When they are sitting next to my Arduino, everything is fine. When they are ~ 3-4 m away, the Arduino gets no signal (or more times doesn't get the right signal).
At that time I am using a simple ~17 cm long wire that is curly to save space soldered to the "antenna port".
What can I change in order to get a better signal?
Are you sure that your module works well to 12 V?
Since it is the "XY-MK-5V" model I think it has the voltage up to 5 V as ideal.
For all I know, these modules work well between 3.3 V and 5 V, maybe saturating the circuit.
Really, the transmitter work with up to 12 V.
But I suspect that it does not work at the frequency in question. See, there are a lot of bad information on the Internet about them.
See more at: How to use 315 MHz RF transmitter and receiver modules with an Arduino