This is a tale of two USB SDR dongles:
On the left is a no-name cheepie USB SDR from Amazon, $13.
On the right is the NooElec NESDR Mini 2 SDR using a R820T2, with improved crystal and other components, $26 (http://www.nooelec.com/store/sdr/sdr-receivers/nesdr-mini2-rtl2832u-r820t2.html
The NooElec SDR is twice the price of the no name. Is it worth it?
Executive summary: For me, the NooElec NESDR is worth it. PiAware reports 4% to 6% more aircraft and positions than the no-name. Dump1090-mutability reports the NESDR decodes twice as many messages per second as the no-name.
I tested both SDRs at the same time using the same RF chain: a discone antenna on the roof feeding a high-pass filter, low noise amplifier, and surface acoustic wave (SAW) bandpass filter centered on 1090 MHz. The SAW is followed by a Mini Circuits ZX10-2-20 signal splitter. The splitter feeds the two SDRs using high quality SMA cables and SMA to MCX adapters. Both Raspberry Pi systems are running the same software, dump1090-mutability (using the same configuration, including AGC) and PiAware 1.19.
Ran this setup for 48 hours, collecting not only daily numbers from PiAware, but also the occasional hourly sample. Also watched data on the two dump1090 web pages.
This test evaluated the two SDRs in terms of the numbers they report to PiAware: positions reported and aircraft seen. Other characteristics such as frequency stability were not directly evaluated; only the numbers from PiAware mattered.
According to PiAware, the NooElec NESDR reports 4% to 6% more positions and 4% to 6% more aircraft seen, compared to the no-name SDR. I switched splitter connections at the end of the first 24 hours; that didn’t change the results for the second 24 hours. For example, the NESDR reported 144867 positions and 1453 aircraft over a 24 hour period. The no-name reported 138040 positions and 1344 aircraft over the same 24 hour period.
Looking at the dump1090 web pages, the NESDR consistently reports twice the number of messages per second in comparison to the no name (dump1090-mutability shows this on the web page).