Over on Reddit user MaxWorm has been doing some experiments with comparing various RTL-SDR dongles on L-band (1 – 2 GHz) reception. Previously we wrote a tutorial on decoding Inmarsat signals which are at around 1.5 GHz and noted that the R802T/2 dongles can have some trouble at these frequencies.
It is known that the R820T/2 is not as good as the older now rare and expensive E4000 tuners at frequencies above 1.5 GHz, and it is also known that sensitivity decreases as the temperature of the R820T/2 increases, especially at frequencies above 1.5 GHz.
MaxWorm tested an R820T, R820T2 and two E4000 sticks at receiving L-band frequencies. He found that one of the E4000’s performed the best, but surprisingly the other E4000 dongle was totally deaf in the L-band. The R820T and R820T2 dongles performed similarly – not as good as the best E4000, but not as bad as the worst. All tuners exhibited reduced signal strength when warm.
In another post MaxWorm also measured the temperature of the tuner chips in each of his units, and created a simple heatsink for one of his R820T2 dongles. His results show that the heatsink passive cooling works well, significantly cooling the R820T2 chip. His measurements are copied below:
R820T2 in Plastic case:
R820T2: 77°C top / 74°C bottom
RTL2832: 56°C top / 54°C bottomR820T2 bare PCB:
R820T2: 62°C top / 63°C bottom
RTL2832: 43°C top / 42°C bottomR820T2 in Alu-Case with Alu “L-Bridge” on Tuner:
R820T2: top 37°C / bottom 47°C
RTL2832: top 49°C / bottom 40°CE4000 in plastic case:
E4000: 37°C top / 37°C bottom
RTL2832: 46°C top / 40°C bottombare E4000 PCB:
E4000: 37°C top / 32°C bottom
RTL2832: 40°C top / 37°C bottom
Other experimenters have previously applied fan cooling and oil cooling to RTL-SDR dongles to cool them and increase sensitivity.
RTL-SDR with heat sink on the R820T2 chip connectoed to the aluminium case. 
L-Band Reception Results for an R820T, R820T2 and two E4000 dongles.
Comparing RTL-SDR’s on L-Band Reception, Tuner Temperatures and Passive Cooling
Source: RTL SDR