ADS-B Reception RTL vs Airspy

I’ve recently been playing with ADS-B reception to test new revisions of my 1090Mhz ADS-B Preamp. With my location 300 meters ASL and between two international airports I’m ideally placed for reception. I wanted to see what difference there was between the nice and cheap RTL dongles and the Airspy SDR.

I had previously installed an A3 ADS-B antenna from in my loft:

2015-04-18 09.49.13

You can see the preamp on the left. The indoor location is far from ideal but I currently don’t have space on the mast outside to fit it and as you can see by the results below its still performing well. At some point it will move outside. The antenna is connected using Belden RG6 with some nice quality SMA connectors from Barenco.

The preamp is a Uputronics ADS-B 1090Mhz preamp with SAW filter. Based around the Minicircuits PSA4-5043+ it provides approximately 14dB of gain at 1090Mhz and has a Golledge SAW filter to remove out of band inter-modulation.

To enable a side by side comparison of the two receivers the feed was connected into a Minicircuits ZAPD-2DC-S+ power splitter. The Airspy with its ability to provide power to the preamp via bias tee was connected to the DC pass through port. The RTL was connected to the other RF port:

2015-05-09 10.35.07

A quick word on the dongle, its an older Elonics E4000 based model the only modification is the Belling-Lee connect was removed and replaced with an SMA connector. Otherwise its stock.

SDRSharp’s ADSBSharp and ADSBSpy V1.0.0.11 (Link is latest V1.0.0.12) programs to drive the dongles these fed into Virtual Radar Server and ADSB Scope. To ensure no issues both dongles were on separate USB3 buses. After briefly adjusting the gain on both dongles to get the optimal reception I left them to run for about 28 hours on a week day.

At this point its worth noting, ADSBSpy suppresses duplicate frames and it doesn’t try to correct frames with bad CRC. This is preferred by sites such as such as FR24 and PlanePlotter’s sharing network as the CRC is weak and it can result in erroneous data being uploaded to their servers. ADSBSharp does correct frames with bad CRC and doesn’t do any duplicate detection so I would expect more frames and position reports from ADSBSharp.

So the results. Firstly range :

As you can see the overall range is generally limited by geography from my location and in certain directions both radios are getting pretty close to the radio horizon.The outer ring is 400km of which both radios managed to exceed reception. However fairly consistently the Airspy exceeded the range of the RTL in some areas by over 50km.

In the 28 hour period the RTL returned the following stats :

TotalMessages Recieved : 2,910,780
AirbornePosition : 1,345,245
AirborneVelocity : 1,342,768

The Airspy :

TotalMessages Recieved : 10,307,631
AirbornePosition : 4,836,796
AirborneVelocity : 4,410,924

The numbers speak for themselves really, the other interesting number is the number of unusable frames with the RTL was 3.4million with the Airspy it was 305!

When you consider the results from the Airspy contained no duplication or corrected CRC the results are even more impressive. So in conclusion if you are serious about ADS-B reception the Airspy with a preamp is the way to go. I suspect it will give the hardware based ADS-B receivers a run for their money too whilst being significantly cheaper (If anyone wants to supply me one I’m happy to do a head to head!)

  1. RTL-SDR vs. Airspy on ADS-B Reception - - pingback on 09/05/2015 at 23:58
  2. Many thanks for the comparison. Any chance that you might repeat this comparison, but this time using an R820T/2 based dongle? I have both R820T and /T2 based dongles, and the /T2s are significantly more sensitive than the older version. I suspect that the new dongles would be up to par with the Airspy.
    One more question – how does the reception compare with and without your pre-amp with SAW filter. Thanks!

  3. Hi there. I’ll get hold of a R820T based one and revisit this test. Happy to do the test without the preamp too though I can’t back to back with and without that one as I’d need two runs of coax coming down from the roof. I did some quick tests with and without preamp and range was reduced and there were ~50% less messages received but I’ll do it properly in the near future.

  4. Thanks Anthony!

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