Couldn’t find this particular case addressed when I searched the forum.
I have been looking more closely at my different stations message rates and noticed that my highest message rate station doesn’t always yield the most positions reported.
Station 116429 has a Blue FlightAware SDR and Station 117319 is using a Nooelec SMArTee SDR with their SAWbird LNA/Filter connected right after the antenna. The stations are separated by 5 feet.
Station 117319 often shows 1.5x-2x the message rate of Station 116429. I have never witnessed Station 116429 reporting a higher message rate. Today (3/24), I noted the peak message rate of Station 117319 at around 680 messages/sec and Station 116429 at 450 messages/sec. However, Station 116429 still reported more positions for 3/24 and this happens a lot going back through the daily stats.
Any suggestions? Does a message not necessarily mean the station is collecting/reporting a position? Thanks.
Making assumption the pi’s and the software are identical. Grandpa always taught me not to assume anything. First, install the graph1090 package, probably the best diagnostic tool we have. Thanks wiedehopf for this tool. (copied from another thread)
Tough to diagnose based on only one set of values. Perhaps swap the receiver/pi positions, and see if the pattern stays with the antenna or the receiver/pi components. That gives you a baseline to suspect one or the other. Antennas may be at 5 ft, but small changes in the surroundings like window frames or metal items can make a big difference. Indoor or Outdoor? Perhaps swap the SD cards and see if that makes a difference. Diagnose by making a change and seeing the differences.
Are the SDR’s connected to the same sockets with identical USB cables (if cables are used)? Gain settings?
Your graphs will tell you what is happening in your systems. Have fun optimizing both systems. Hope this helps, others here probably have better ideas to chase down the differences.
Both are Raspberry Pi 4s using the latest Raspberry Pi OS (not the piaware image). Both are using an antenna of the same design and are located indoors. Station 116429 uses RG-58 cable and Station 117319 uses “KMR400” (a knockoff of LMR400). Just changed the cable from RG-58 on 117319 on 3/23, but the trend of 116429 reporting more positions goes back before then so I don’t think the new cable has made an impact. Both cables are 15ft in length. 116429 has the SDR plugged directly into the Pi but 117319 has a USB hub for the two SDRs (one for 1090 and one for 978). I will try plugging them both directly into the Pi tomorrow to see if that changes anything.
As you have said, antenna positioning makes a big difference and I have noted that with small changes in positioning as little as 1 foot. I thought the substantially higher message rate from 117319 in its current position would then yield the most positions reported. Never changed any gain settings on any of my installations.
Will install graph1090 tomorrow and also look into changing the gain settings. Going to save hardware swapping/repositioning as the last resort, my installations are all expertly mounted to my walls with many pieces of painters tape.
Sorry about being ambiguous on the moving systems. I should have said swapping cables to the antennas and leaving the antennas in their current locations. Painter’s tape works for me too. I hope this does not ramble around too as I write and think.
First, install graph1090 and collect at least a day or so to fill up the initial graphs. That will give you a baseline to compare future changes. Add it to all 4 of your systems if you can. The signal level graph will give you a good idea on adjusting gain and AGC settings.
I looked at both site pages, and looking at the coverage graphs. Station 116420 has the higher loss cable to the Blue FA dongle. The 117319 station with the LNA at the antenna and low loss cable may account for the different performance. SDR’s can be overloaded a bit and get a bit deaf until the receiver recovers. Just guessing, the 116420/FA dongle with the higher loss cable is less affected by close by planes and can continue to hear more planes. The 117319 system has a much higher signal level (based on the coverage graph, and LNA) and receives over a larger area, but the close by planes may cause the overall system to go deaf for longer periods, missing some planes. Deafness is shown sometimes by dotted lines on the PiAware SkyAware page.
After you have a baseline set of graphs1090, test to see if the antenna positions are a factor, by swapping the cables and LNA at the antennas, leaving everything else unchanged. If the stations retain the previous messages/planes, then the antennas and their positions are not the issue.
How far apart are the antennas? Preferably, at least 20 inches or more as they do interact if they are close. Stay away from any metal items. I live in stormy Florida, USA. One test system had major differences depending on where in a window with metal storm shutters it was located. At these frequencies, inside a home, small moves will affect how the antennas perform.
It may take a couple of changes and days, but you will get this figured out.
Gene
I installed graphs1090 on 3 out of 4 of my installations (the 4th one is a FlightFeeder). 116429 is using only an ADS-B antenna while 117319 has both ADS-B/UAT. The LNA is dual purpose for ADS-B/UAT and is one unit. The antennas are hooked directly into the antenna inputs of the unit and have about an inch of separation. ADS-B performance hasn’t degraded since installing the LNA as far as I can tell (it hasn’t helped it either). UAT performance has gone up quite a bit however.
graphs1090 has only been running for about an hour. The tool is showing the gain of 117319 at 28 dB and ADS-B mean median signal level at -14.3 dBFS while 116429 gain is at 49.6 dB and the ADS-B mean median signal level is at -19.8 dbFS. Will need to let this run some more and report back my findings.
Going to make changes to cabling/antennas and see the outcome. The images still appear to show Station 117319 collecting more messages/positions per second than Station 116429, but Station 116429 somehow still shows a higher total position count for 3/26 on the FlightAware stats page.
Personally, i think that you may want to investigate the aparently high noise levels on both stations. Makes it rather hard to get good range when weaker ads-b signals are “quiter” than your noise level.
(High RF/RF noise, local RF noise - hdmi, cell sites ?)
On the noise front, the stations don’t have any other wiring or electronics near them. However, there are 1000s of other apartments nearby which brings a lot of potential for noise. I noticed some slight variations based on changes to antenna positioning and looking at the real-time stats having planes “Last Seen” while not necessary having the “Last Position” keep pace (for example Last Seen 1.1s ago and Last Position 34.7s ago).
Station 117319: Over the past ~2 weeks I have tried different SDRs, not using the Nooelec SAWbird, moving the antenna, and finally installing an Airspy Mini. In the images below, the Nooelec SAWbird is utilized from 25-27 March and from 5-7 April. When not using the Nooelec SAWbird with Nooelec SDR, the blue ADSBExchange SDR was used (it has a built in filter and LNA). Between the ADS-B Message Rate and ADS-B Maxima graphs, it appears the Nooelec SAWbird gives a slight advantage. Installing the Airspy Mini for 6-7 April shows a clear uptick in message rate.
Doesn’t seem the uptick in air traffic was related to the eclipse as Station 116429 (to which no changes were made) is showing steady message rates over the past several days.
With the installation of the Airspy Mini, Station 117319 is now outperforming Station 116429. Not sure if my stations ever picked up a balloon before, but saw one after installing the Airspy Mini. Checking my 3 other stations at the time, none of them were seeing the balloon.
