Software Defined Radio (SDR) has finally reached a much broader mass of people, who wanted to play with RF technology, but didn't find the time or resources to learn all necessary skills, to build a hardware based radio. Thanks to the work of the GNU-Radio and OsmoCom developer crowd, this barrier is finally gone and everyone can, more or less, directly access, what the antenna receives.
Good news for anyone playing and developing cheap SDR technology with the Elonics E4000 (e4k) tuner chip: Until now, working with the chip has mostly been guesswork and trial and error through reverse engineering, in order to get the SDR's to work. Today the complete Elonics E4000 reference documentation was leaked, so grab and mirror the e4k datasheets and application notes, while they are hot and available:
Soon after the release of RTL-SDR a lot of people started to play with software defined radios. Although the Elonics E4000 tuner and the Realtek RTL2832U Chip are a long way from the quality and performance/stability of an USRP(2), the price of $11 - EUR30 makes these devices an ideal beginners device for SDR experiments, without having to invest +$1k into hardware.
The UmTRX is a dual-channel, wide-band SDR transceiver (so it can send & receive) with 1GbE connection. It is developed by Fairwaves team to be used as a transceiver for OpenBTS GSM base stations, but due to its software defined nature, it could be used for many other radio applications as well.