The one's from Spark Fun do not have an analog (i.e. linear) output. That's not much of an issue unless you want to measure the received signal strength.
The TWS/RWS (Wen Shing) are available from many dealers worldwide and have been cloned by several manufacturers.
Here's another, dirt cheap, source. [url}http://www.e-madeinchn.com/Product.htm[/url]
ASK (Amplitude Shift Keying or On Off Keying) is AM and FSK (Frequency Shift Keying) is FM. Most FSK modules cost more but you can use their Carrier Detect pin to tell when a signal is present, doing away with any need for sync bytes or start-of-frame pulses.
Range (i.e. distance) is independent of baud rate and is almost 100% a function of transmit power (severely limited by the FCC) and environment. It is, however, easy to increase range by improving the receiving antenna, adding preamplification, etc. Some receivers (e.g. the dirt cheap ones above) cannot handle a preamp, others (e.g. Wen Shing) can handle 2-3 cascaded.
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