Poor FlightAware ProStick Plus performance vs other dongles

synoptica · January 29, 2021, 11:51pm

Hi all,

Over the past 9 months or so, I’ve been collating a lot of data from various ADSB receiver combinations, using RTL-SDR Blog v3, RadarBox and FlightAware dongles, and various antenna setups, with and without an LNA, with the long-term goal of doing a writeup on what I’ve found the best bang-for-buck combination to be (I won’t give away too much now, but the result are not what I expected!)

One thing that has frustrated me the most is the poor performance of the FA ProStick Plus. This performs worse than, to at best maybe on par with, a stock RTL-SDR dongle. This is in stark comparison to the RadarBox dongle which gives a very noticeable performance gain.

I’m using an up-to-date version of dump1090-fa, auto gain control (which I’ve used across all dongles, I live very close to an airport so I find that fixing my gain tends to overload as I see a lot of air traffic within only 1km or so) and at the moment, no LNA. Dongle was purchased from RTL-SDR Blog so I’m certain it’s genuine.

Setups are otherwise 100% identical, same Raspberry Pi, same software, same antenna, same cables, just swapping the dongles only.

Any other ideas or suggestions before I send this back?

abcd567 · January 30, 2021, 12:14am

(1) Reduce gain to say 42 or 38 and see if it improves.

(2) If reducing gain does not help, then add a filter to FA proStick Pus, and most likely it will be OK.

synoptica · January 30, 2021, 12:19am

Thanks @abcd567 - I’ll have a play with the gain and see.

The filter I’m a bit more skeptical on - given the FAPS+ is a dedicated ASDB dongle, I would have expected it to perform on-par to my RadarBox dongle. If there is extra filtering and amplification on the FAPS+ for ADSB specifically, I can’t understand why I’m seeing worse performance out of the box!

obj · January 30, 2021, 2:36am

I assume by AGC you mean --gain -10 or equivalent. This does not actually give you any sort of gain control - with ADS-B, it effectively forces the gain to maximum, higher than you can usually set due to librtlsdr gain-setting quirks.

So you’re probably overloading the PS+. Nearby airport + dongle with an extra LNA + max gain is probably the worst combination you can get. As abcd said, try reducing the gain.

You should expect to have to set different gains on the different dongles that you have; they each have different frontend gains to deal with.

synoptica · January 30, 2021, 2:56am

@obj That’s a brilliant answer and exactly what I was after, thanks!

My original testing, performed with a stock RTL-SDR Blog v3 dongle, consistently yielded worse performance with fixed gain settings rather than AGC (–gain -10 as you mention). I have not done any such testing with either the RadarBox or PS+ dongles!

I’m aware of scripts etc that automate this process so I’ll sus these out - thanks again!

abcd567 · January 30, 2021, 3:04am

Before you use scripts, simply reduce gain of ProStick Plus to 36 and watch performance for a while.

SoNic67 · January 30, 2021, 4:46am

In my experience, living close to an airport and under a traffic lane of planes, “automatic gain” was the worse option. That “AGC” was designed for a constant radio signal, from a source like a TV station.
Not for 100 different sources pinging the antenna with short bursts of different values of amplitude 400-600 times a second.

wiedehopf · January 30, 2021, 8:12am

It doesn’t have any amplification so the maximum gain you can get is usually best. You get the maximum gain by setting to -10.

The FA Pro sticks have amplification so using the maximum gain you can get is NOT a good idea.
In some locations the LNA which is in front of the filter will overload due to interference, changing gain will not help you in this case only an additional filter will.

The Radarbox SDR has the filter first then the LNA so it handles interference better while losing some sensitivity.

Thoughts on optimizing gain

synoptica · January 30, 2021, 9:21am

Thanks, will do! I usually err towards a lower value for fixed gain, but that’s working in bands that have a lot of adjacent traffic, not so much of an issue around 1090!

That’s really interesting and is 100% why I bought multiple dongles; thanks for this bit of info!

That’s an interesting anecdote. I’ve been getting some very decent results with AGC; much better than I honestly ever expected, and about on par, mathematically, with where I would expect the range to drop off (e.g. the point at which a plane at 36,000 feet is over the horizon from my location).

foxhunter · January 30, 2021, 10:21am

It also depends on your location, the obstacles there and the noise coming from other sources which can impact your reception
I was using the blue FA stick and changed the antennas over time. Finally with a Jetvision antenna 42.1 was the best gain setting for my location.

I was also using the dark blue (1090) FA filter additionally, but it does not give me any improvement. I only needed to increase gain by 2-3 steps, but here i have obviously “nothing” which can be filtered with it.

What i wanted to say is that it really depends on your individual environment. My location is obviously good for a default setup and the major limitation is the terrain which cannot be improved by using different devices or other settings.

Meanwhile i am operating an Airsquitter (technically a Radarcape device) which is highly optimized. Even with that, the improvement is not significant.

Friend of mine is operating one device in Vienna downtown where the blue FA stick is not sufficient, additional filtering and amplification is required

SoNic67 · January 30, 2021, 3:03pm

See… my quote started with “In my experience”.
That is not an “anecdote” (as in “an account regarded as unreliable or hearsay”), it’s reality. It meant that it depends of traffic in your area. If you have low traffic, at a somehow similar distance from antenna, then AGC might be OK.
Also if your antenna has low gain, or is indoors, then all signals are weak. Even close-by signals won’t overload it, so the AGC will just push the receiver gain to the max (about 55dB) and stay there. In that case moving the antenna might help a lot.

I have a lot of almost overhead planes in the same time with lots of planes at 150 miles. Their signals are emitted in pulses, random times, and the ACG would just not know how to react. It probably will stay at a average gain value (based on an 2-5 second average of those pulses), but definitely won’t work as intended for “AGC” of a single TV station.

What you need in cases like mine is receiver dynamic range. Capacity to decode small signals in presence of large ones. For me that meant I need an Airspy to get most of the signals. Plus a decent filtered LNB.