Nobu Saito, a Japanese RTL-SDR hardware developer has come out with a modified RTL-SDR which has a +-2PPM 28.8MHz Temperature Controller Oscillator (TCXO) instead of the standard 28.8 MHz stock oscillator. (Note this link is machine translated to English from Japanese).
Normally 28.8 MHz TCXO’s are difficult to find, but Nobu was able to find a source in Japan, and he is now selling on his Amazon Store (with international shipping) modified dongles.
The oscillator on the RTL-SDR is prone to thermal drift, which means that as the dongle heats up from use, the frequency you are tuned to may change over time. A TCXO compensates for differences in temperature, and thus keeps the frequency stable as the temperature changes. This is extremely useful for applications such as receiving GPS, Beacons, APT, HFDL, and for radio astronomy.
Nobu sells the modified dongle with TCXO on this page. We expect to receive a sample of his product soon and will write a review when we receive it.