RF modules with RX and TX have a chip that handles the protocol.
The very cheap RF transmitters modules can only switch the transmitter on and off.
I guess you have a very cheap 433MHz RF module.http://www.ebay.com/sch/i.html?_odkw=433mhz&LH_BIN=1&_sop=15&_osacat=0&_from=R40&LH_PrefLoc=2&_nkw=433mhz+-antenna&_sacat=0
The output pin of the receiver module does not reflect the signal strength. You have to hack the circuit to find the signal strength (find the capacitor for the automatic gain control).
For these cheap modules, switching it on and off can not be detected by the receiver, due to the agc (automatic gain control). You have to use a software protocol. The VirtualWire is (the only) good library for that, http://www.open.com.au/mikem/arduino/VirtualWire/