I recently purchased a few of these modules from ebay:http://www.ebay.com/itm/4KM-Long-Range-RF-link-kits-with-encoder-and-decoder-/130545302887?pt=LH_DefaultDomain_0&hash=item1e651b3d67
I believe they are the same as the 2KM ones offered by seeed studio and others.
The problem is, these kits differ from the simple short range kits I have been using. The Tx has four output pins instead of 1, and the Rx has four input pins, as well as a "vt" pin, which indicates that a signal is present.
In addition, you must "pair" the Tx and Rx by soldering some pads on the back, which I have done.
I found a sample program here:http://www.seeedstudio.com/forum/viewtopic.php?f=4&t=309&p=767&hilit=pt2262#p767
Which succeeds in sending data to the receiver "most" of the time. It iterates through the number 1 - 16, and send those numbers as bits. When the receiver detects a signal on it's "signal high" pin it prints the number. Some of the numbers work, some don't. There doesn't seem to be any connection between which number work and which don't.
I have tried just manually setting the pins high and low, but this doesn't seem to work.
I can't seem to figure out how these rf kits work, when compared to the simple 433mhz short range kits I was using.
I intend to use these kits with virtualwire if I can figure out how to use them.
I am nearly certain they work, since I am receiving good data some of the time, it just doesn't seem to work all of the time.
Has anyone out there used these kits, or has anyone got any idea where I might be going wrong?