FlightAware Discussions

Comparing two USB SDR dongles

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.

Technical Discussion:

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).


bob k6rtm

Hi Bob, thanks for the comparison. Are you comparing like with like? The NooElec is an R820T2 so has slightly better sensitivity (2 - 6dB). Is that the difference you are seeing?

Great job Bob. I’m sure someone could throw rocks with “why didn’t you …” but you have to start somewhere. It sounds like the chip sensitivity is the issue. When calibrating my 3 dongles, I found the the offsets varied form -25 - 45 ppm. I assume you adjusted for that with these two. Again great work.

Thanks Bob for the detailed test! I ordered a NooElec R820T2 right after reading your results :slight_smile: I also run a Pi with dump1090-mutability.


Nice experiment!

Could you please tell me what’s the name of RF port on the left dongle. I wanna buy a better antenna for it but don’t know what kind of connector is suitable.

The connector on the SDR dongle is a female MCX. You can get adapters from MCX to other standards. Since I use mostly SMA connectors on cables and devices, I use a male MCX to female SMA adapter.

Does this help?’

bob k6rtm

among other sources:
amazon.com/coaxial-coax-adad … +connector

Very helpful, thanks a lot.

Besides,do you know if this antenna is suitable for DVT-T dongle?

It’s provided by FR24 for their official ADS-B receiver, FR24 Box.

Good morning, Bob -

Nicely done. Without testing like this, it’s hard for the rest of us to be able to make decisions about all the different components which are available out there.

Cheers and 73 - Jon N7UV

Thanks Bob. Will be ordering one here in a couple days after your report :slight_smile:

bob k6rtm,

This question comes from a place of respect and jealously…
Are you retired?

Man the projects I could complete and toys and things I could do with more free time.

Edit… I r grammer much.

Free time in retirement is somewhat of an urban legend I speak from experience. :slight_smile:

WARNING: philosophizing ahead

Am I retired? Interesting question. I don’t want to think so. I’m currently working with a startup in search of funding. This is one of the things I do for fun (and possibly to avoid other things I should be doing – see for example, “avoidance behavior”).

We never have enough time – time is the most precious commodity. There’s never enough time.

Yet we must make time for the things that are important. And one of those is unwinding, relaxing, having fun. That and sleep. Sleep is very important.

End philosophizing (or was it bullsh*).

Side story –

A while ago I ran into a colleague form the past, someone I hadn’t seen in a couple of years.
Me – Ira! good to see you! what are you doing these days?
Ira – I’m retired.
Me – that’s great? When did that happen?
Ira – About a year ago, but I just figured it out recently.

That’s where I am…

Ordered one off EBAY today. I couldnt go direct to the company as the Gift card I had wouldnt allow orders from Canada.

Anything I need to do special Bob or just plug er in?

Thanks for taking it in the humors way it was intended.
I have a birthday coming up and the wife laments that she cant buy me anything as the only thing I ask for is time. Time for finish projects, spend it friends, SLEEP and yet not miss anything.
Time the one thing money can’t buy. :wink:
Congrats on finally realizing you are retired!

Also thanks for your postings!

Well, you could just plug it in – the software should recognize it.

Or – since you have a few days, you could gather data as I described in a different thread. Find a PiAware station close to you that has similar stats and looks stable. Compare those stats with your station; hopefully you’ll find one that gives you a narrow range of comparisons on both positions reported and aircraft spotted.

Then when your new SDR arrives, you can switch it in, monitor the numbers, and measure the difference.

In any event, have fun!

bob k6rtm

I don’t know that comparing your feed to someone else’s is valid

…these screenshots are from ‘heywhatsthat.com … in the air’, this gives a reasonable correspondence to what I actually do see.
Image 1: what I see
Image 2: what I would see if I was 1/2 mile to SE (on top of the 30ft rise that blocks my view in that direction) - the orange line indicates I would see much of the London Heathrow traffic
Image 3: what I woud see if I was about 4 miles SW (on top of the local big hill)

http://i58.tinypic.com/dlm04g.gif http://i62.tinypic.com/25kr6g5.gif http://i57.tinypic.com/14eb8yp.gif

?The data in this comparison was limited to the two SDRs running from the same RF feed. I did use the local reference station to see if this test was changing performance overall, but that wasn’t part of the core experiment.

I agree that comparing your feed to someone else’s must to be done carefully – if I moved my station a mile and a half to the West to a friend’s place, it would be up another 1000 feet or so and while the West would be even more shaded, the view otherwise would be even better. (I’d set up a feeder there but they don’t have reliable Internet service, and putting up a point-to-point microwave link for this is absurd – but doable.)

That’s why I mentioned in my choice of reference station someone with about the same numbers, stable, and even similar topology. I think the similar numbers works out most of those details – if the numbers are close and stable over a period of days, that’s what you’re looking for, right? Over a period of days your’e going to average out the typical traffic patterns.

The topology/terrain we have in Silicon Valley makes those selections relatively easy. But I did put some effort into making the selection, tracking a number of sites for about a week before going with one.

Viewing this as an aspect of experimental design, it’s another one of those nasty real-world issues that makes this stuff challenging (and for some, fun). It’s another aspect of picking signal out of the noise and working with it.

Thank you for the question. Keep poking at my assumptions – we learn by making mistakes – I’ve learned a lot over the years and look forward to learning a lot more! I think some folks are waiting for me to build/try a co-linear antenna, post data on it, and change my tune…

Keep asking questions, keep thinking, and keep having fun!

bob k6rtm

I’m more curious on the eggbeater idea. :smiley: