Over on YouTube user Adam Alicajic has recently been uploading videos that show him testing a prototype of his upcoming product the MIX4ALL. The MIX4ALL is an RF downconverter which will allow the RTL-SDR to receive signals at around 1.5 GHz or higher. Although the RTL-SDR can already tune up to ~1.7 GHz, above about 1.2 GHz sensitivity is poor and some units have problems receiving when they get hot. The downconverter will convert a 1.5 GHz signal into a signal at around 250 MHz, where the RTL-SDR operates well. At around 1.5 GHz there are several satellite signals of interest including Inmarsat EGC, Iridium and AERO signals.
On one video Adam decided to use the MIX4ALL to test the difference between a GPS patch antenna and a home made air gap patch antenna. The GPS patch antenna was salvaged from an old GPS receiver and the patch antenna is the one discussed in this previous post. In the test Adam used the MIX4ALL and an RTL-SDR, and tested reception of Inmarsat signals. His results showed that the reception given by the GPS patch was very poor compared to the home made patch antenna.
Some other recent videos by Adam show him also testing his MIX4ALL with S-Band signals around 2.3 GHz and also receiving Alphasat XL.