RTL2832 USB receiver comparison

This is about the USB dongles which turn your PC / Laptop or even Android phone into a full range scanner receiver. Most of them are described as RTL2832U, named by the chip. But they use different tuner variants. Higher priced devices like Airspy raise hopes to give better results with an improved physical architecture. I've tested three devices using SDR sharp (#) software on 3 frequencies with weak signals focussing on sensitivity and intermodulations:

Test frequencies

49.75 MHz: R1 analog TV carrier, with regular MS (meteor scatter) pings here in North Germany
99.7 MHz: weak signal from NDR Info, Kiel (60km, 400W, antenna not directed to it)
229.75 MHz: cable TV audio channel from the neighbourhood, very weak on my antenna but useful for tests as it produces a constant signal

Gain settings were always adjusted to get the best SNR.

Devices

Airspy Mini (99€) produced in 2017
T820 tuner 20€ purchased about 2013 (the black one)
T820T2 tuner (20€) from rtl-sdr.com (advertised as RTL-SDR v3), purchased 2018

Results

Sensitivity was almost equal.
The Airpsy Mini showed more intermodulations on the FM band than the cheaper devices. The T820 was intermodulation-free around 49.75 MHz, RTLv3 and Airspy were not. Major intermodulations appear even if you reduce gain a lot.
Centering the frequency helped to reduce intermodulation with the cheaper devices. The Airspy had a strong intermodulation on 99.2 MHz which even appeared when centering it.
With the T820 results depend very much on the used bandwidths. Different BWs produce different intermodulations. 0.25 and 3.2 MSPS should better not be used, everythin in between (0,9/1.024,1.4/1.8/1.92/2.048/2.4/2.8 MSPS) works fine.
The Airspy Mini offers 3 and 6 MSPS. With 3 MSPS the sensitivity on the edges of the spectrum is reduced, probably by bandpass filtering. 6 MSPS is flat on frequencies below the center but not attenuated close to the higher limit.
Offset calibration worked on both T820 but not with the Airspy Mini
The Perseus receiver (more expensive and not a RTL device) with FM+ converter was completely intermodulation-free on the used antenna setting. Sensitivity on 99.7 was only equal though.

Peer-Axel Kroeske, May 2018

Radiovibrations.com -> test reports