Yes, I spent some time yesterday as well trying to get the 2KM RF kit to work.
As Albert said, it does not work when they are very close to each other, probably the receiver circuit does into saturation and is overwhelmed by the RF signal. I basically used a similar test application as Albert has posted, just attach 5 LEDs to the receiver and wire up the transmitter and receiver to use the same address code bits and then set the transmitter data Pins (D0 - D3) to HIGH using a wire or switch.
These modules are using the PT2262/2272 Encoder/Decoder ICs and it seems to me that these ICs are set to an oscillator frequency of about 500Hz. And since each data word consists of 12 bits (8 for address and 4 for data), the theoretical communication rate is very low.
I was hoping I could use these to transmit up to 4 bits of data simultaneously from a Microcontroller at a decent speed (> 1000 bits/sec).
Anyway, I don't think these modules can be used for any useful data transmission from a Microcontroller, since I think the speed is too low. They probably work well as a remote control where you have 4 switches and turn one switch on at a time.
The way the encoder/decoder works it's waiting for at least 2 frames with the correct address bits before the VT pin is turned on, so you can't even use this module to send anything more than maybe 1 or 2 bits/second ..
Albert, can this module be used from a Seeduino? What is the max data transfer rate?
In my testing if I turn one pin on on the transmitter (e.g. D0), the receiver light's up one LED, when I and then turn another one on (e.g. D1) the receiver still only sees one LED. Only if I turn the first switch off and then both switches on will the receiver see 2 LEDs. So it seems to me that VT has to go to LOW before a different LED can be turned on, is that correct?
If they can't be used effectively with a Microcontroller, then it may be a good idea to list that in the product description, unless I am using it wrong.