Sampling at 250 kHz without aliasing

We have a need for a small sample rate on the rtl-sdr. We have been able to select a bandwidth of 250 kHz, but there is significant aliasing at that setting. At higher sample rates the aliasing no longer exists. We are using the dongle that is sold by the RTL-SDR.com blog: http://www.rtl-sdr.com/new-products-rtl-sdr-with-1ppm-tcxo-sma-f-connector-… Since a reduced sample rate would allow for a much less resource consumption by the CPU, we would gladly sponsor an open source bounty or pay for open source development work to address this problem. Our use case is reception of a 5 kHz channel from a geostationary L-band operator. We have found that the dongle gets very hot at 1550 MHz, so we will use an LNB to downconvert to ~400 MHz. The rest of the RF chain consists of a patch antenna with 8 dBi of gain and 17 dBW EIRP from the spacecraft. The demodulator will be running on a derivative of the Beagle Bone Black. The designs for this board are available here: https://github.com/outernet-project/lantern-compute-pcb You can learn more about Outernet through the following links. http://gizmodo.com/what-is-the-outernet-and-is-it-the-future-of-the-intern-… http://www.wired.com/2015/07/plan-beam-web-3-billion-unconnected-humans/ http://www.technologyreview.com/news/537411/startup-beams-the-webs-most-imp…