Hello @bmcent1, you may find it useful to review your gain setting and see if there’s room to optimse it a little. I wrote an article about it based on an interesting blog post.
The idea is to adjust the gain setting for your setup and your location, such that you maximise the message rate across the entire signal range of the receiver. You can find the right setting in quite a short time using this approach. The post and link to the article explains more.
In my experience the Prostick Plus has outperformed every other device I’ve tried, although I’ve not tried the AirSpy Mini.
I found a big improvement by adding a Uputronics 1090Mhz SAW filter into my setup, which is also a windowstill setup. I’m using the FlightAware external antenna but mounted on a short pole on the windowsill (actually a kitchen roll holder!).
I then found a ffurther improvement in that setup by a) moving the Uputronics filter so it was directly below the antenna (attached with a N-type to SMA coupler) instead of directly attached to the Pi, and b) replacing the short 1m run of CFL200 coax with a short 1m run of LMR400 coax, and using a 1m USB cable to power the Uputronics instead of using a short cable next to the Pi. I wouldn’t have expected it to matter for such a small run but in fact it did, and then I was able to redo my gain setting again and find a slightly different new optimum.
@wiedehopf is the best person to answer this. In my opinion, this is possibly because of diffrent default “age” settings.
In Skyaware map, “age” setting is 60 seconds, i.e. the aircraft disappears if no signal is recieved for 60 seconds. It seems in tar1090 age setting is a bit longer, may be say 70 seconds. This will result in airaft staying visible longer on tar1090 map, which in turn results in more aircraft displayed on tar1090 map than on skyaware map.
Neither Skyaware nor tar1090 feed data to any site. These simply display the aircraft using the data from the decoder. The software “piaware” receives data from the decoder and sends it to Flightaware.
Various different decoder software are available like readsb, dump1090-fa, dump1090-mutability, ModeSDeco2. The most popular decoders are dump1090-fa and readsb. Which one of above noted decoders you have installed on your Pi?
Much wider view, still in a window. Way more tracks colored in, and reaching right up to some of the edges of what’s possible via HeyWhatsThat.
AirSpy mini arrived! I haven’t set it up yet because I’m waiting on a splitter so I can split the 5.5dBi antenna to 2 Pis and test the AirSpy + Filter and LNA side by side with the FA ProStick Plus from the same antenna.
Since FA ProStick+ has filter and LNA in it, what is the better comparison setup?
A)
Antenna -> Splitter -> |- FA ProStick Plus
|- Uputronics Filter + LNA -> AirSpy Mini`
B)
Antenna -> Uputronics Filter + LNA -> Splitter -> |- FA Prostick Plus
|- AirSpy Mini
Not when it follows the LNA (option B).
It will be fine.
The LNA will determine the noise figure.
The Uputronics LNA has a gain of 14dB and a noise figure of 0.75 once you go through the splitter you will lose 3dB but you will still have a gain of 11dB and a noise figure of 0.9
Used the B option from above, and found initially the airspy mini is reporting about 1-2 more planes, 0-2 more planes with positions, and about 15% more messages/s than the FA ProStick +. It’s late and traffic has significantly decreased for the day. Will see what afternoon peak looks like tomorrow.
Here’s screenshot side by side of what I was seeing. Airspy on the left, FA PS+ on right. I used a command line to open both browser tabs at exactly the same time.
That’s using wiedehopf’s defaults for the airspy_mini. Can ignore the claimed gain on the right, was using the nifty tool to play with it, but it doesn’t reflect the current setting of dynamic gain. On the FA PS+, I’d previously tried to fine tune the gain to stay below -2 rssi max, and above -30, ran for 24 hours like that and then ran the next 24 hours with the dynamic gain enabled. (I understand the reasons behind choosing not to use automatic gain but in the back to back 24 hour tests, the results were nearly identical even though the chosen gain settings were quite different.) There were a few more planes out of thousands with the lower gain / a few more positions with the AGC. I found 42.1, AGC found 49.6 … maybe I’ll split the difference. Anyway, it’s convienent at the moment since adding the Uputronics above the splitter increased gain via LNA, dump1090-fa lowered the gain automatically.
Not finished testing but figured to share the initial results
Question about Position History… when both tabs are opened at the same time, airspy initially starts with about 2000 fewer. But leaving tabs running side by side for 30 minutes or so and AirSpy has 2000 more. Maybe that’s a difference between airspy_adsb and dump1090-fa in how they report to skyaware when the web page loads?
As expected. The Airspy outperforms other sticks in most of the cases. It would be interesting (just for comparison) to run the same setup with the FA stick and the LNA which you used for the Airspy. Could improve this as well.
This is actually with the LNA, it’s setup B show a little higher up in this thread. So it’s as true a comparison as I can think of with both using the same antenna. That said, two caveats:
To use one antenna, a high quality splitter was connected between the LNA+Filter and the dongles. So both are equally experiencing a 3dB loss, they might both perform a little better without the splitter.
Before the splitter arrived, I did try the Uputronics LNA+Filter on the Blue FA stick. It seemed to actually reduce it’s capability by a small but noticeable amount. My guess is that the sticks internal LNA and filter are good enough that nothing is gained by adding another. That was with adaptive dynamic range (it’s set to on for both sticks for now), so while it might not have been the absolute optimal gain, it did automatically adjust downward when the external LNA was added.
After running this setup for more than 24 hours, here are some details and a nice picture…
Airspy outperformed the FA stick (blue) in all of the following stats, mostly marginally:
That’s a reasonable result, but useless for an average station. The better capability to discriminate overlapping frames is only useful when the terrain is not the limiting factor.
To determine a position, 2 DF17 CPR messages within 10 seconds are needed in dump1090-fa.
That needs better reception as just receiving some messages from an aircraft.
The 10 second limitation for CPR messages in dump1090-fa is handled a bit different in readsb as well as some other stuff.
But the principle remains the same, it needs better reception to get a position than just getting some data from an aircraft.
Does readsb possibly integrate better with graphs1090? That might be a silly question but one thing I miss currently with the airspy, particularly while I’m doing this head to head comparison with RTL v4 … is that the airspy graphs1090 has fewer panels and seems to lack the max distance stat. Could I get more data in the graphs or comparable data by switching to readsb on the pi with the airspy?
