About a year ago, I setup a receiver at my work, on a hangar positioned between an FBO and the terminal. The antenna and cables were pre-existing from a receiver that had been in place previously. Right off the bat, the results were disappointing, as I was only getting a peak range of about 100 miles. Comparatively, my setup at home is around 350 on average.
I thought that this was due to the antenna being installed on the roof of the office section, which was slightly lower than the peak of the adjoining hangar, so I moved the antenna to the peak of the hangar. This unfortunately did not help, and the range decreased further. I tried a filter, and that did not help either.
I’ve attached pictures of the location of the original install location, as well as the new location. In the second photo, you can see the roofline that the original install was on. I’ve also attached the graphs from the past year, with a red line showing the day that the location changed, and a more recent graph.
One thing to note is that the hangar has a steel roof. I’m not sure if this would have a negative impact.
Does anyone know what could be causing such poor results?
You have a lot of tracks with single message. Are the cellphone towers nearby? They may be causing interference.
Is your range limited by terrain? I think I had that range from a setup I had years ago with the antenna on my basement window bars.
Could there have been water in the Antenna or Coax line?
Thinking while I type. With the relatively high CPU usage vs # of planes, seems like a low power Pi system. Signal levels look ok, and can see your gain is at max. So, not much to go on, and seems like you are losing most of the signals before they get to your receiver. Likely problems are the antenna, connections and possible water in the cable and/or the antenna. The steel roof probably helps the reception.
To diagnose the problems, I would first try a separate antenna directly connected to the SDR receiver and then to the Pi. Power it via a battery or extension and put it outside. It should work better with a different antenna and no cable. @abcd567 has some nifty DIY antennas that work remarkably well.
Just feels like when the system was first removed, rain may have gotten into the old cable at some point. It could also have gotten into the antenna. Substituting parts may be the easiest way do find the problem. I will stay in touch.
No cell phone towers and no terrain. There are a few hangars to the east that are taller, but not by much. I pickup ground tracks on the other side of them without a problem.
I do have a spare antenna so that would be easy enough to try. One thing I just remembered - early on I setup a second receiver, connected to another antenna that was part of the previous system. The two arent the same length, but there was zero different between the two performance wise. I’m semi-suspect of the cable. It is quite long and I don’t know if the quality is good.
Old cable, long, unknown quality, implies a likely culprit for the performance you have. If the cable is about a quarter inch or less in diameter, then definitely has significant losses, and you are losing all the distant traffic. Only the strong local traffic can survive the cable run.
Do you connect via WIFI or Ethernet connection? If WIFI, then perhaps move the receiver much closer to the antenna with a quality cable. If Ethernet, can you route a Cat5E or Cat6 cable to a weather protected location near the antenna, and a short cable to the antenna? Trying to minimize cable losses.
Might help us out here if you can tell us about your setup: kind of Pi, power supply, Operating System, Flight aware installation version, Receiver type, Cable type/length estimate. Does the cable run inside or outside? Do you have a command line interface or full graphic display?
I have been around airport maintenance. Taking a guess, the cable is RG58, often used in airport communications systems and inexpensive. At 1090MHz, 100 ft of RG58 has about 16 db of loss. That means only 4% of the antenna signals actually reach the 100 ft point and less if the length is farther. No range / local traffic only.
This would account for the performance of your system. And if it is an outside run, and water got into the cable, even worse. You could add a filtered Low Noise Amplifier (LNA) at the antenna connection and powered by Bias-T (DC power added to the coax run to power the LNA). If there is water in the line, Bias-T will likely not work reliably if at all.
My apologies, I meant to include this in my earlier response - it’s a RPi3B, NESDR SMARt V5 receiver, running PiAware 9.0.1. Connected to internet with CAT6. The WiFi and Bluetooth options were disabled in config. CanaKit power supply. Cable length is approx 40-50 feet. Type is unknown, but it’s similar in diameter to some LMR240 that I have. With it being that long, I’m probably seeing considerable losses there. I hadn’t considered that previously.
The antenna is mounted to the peak of the hangar outside (reference pixture 2). The cable runs maybe 1-2ft from the antenna before going through a hole and back inside the hangar. The receiver is sitting above the door structure, about 7 ft below the antenna.
Humidity could absolutely be a factor, as I’m only 8 miles from the coast. Whoever installed the antenna/cable previously did not have the N connector wrapped/protected from the elements at all.
@foxhunter I haven’t added anything else, it’s just the receiver connected to the Pi.
That is normally not an indicator. I have a 5 meter cable i bought together with my airsquitter. That’s much thinner than the 3 meter low attenuation cable which is much thicker but has similar values.
Then i am clueless.
I would go with the others who suspect having a new transponder around which disturbs your reception.
If you have an external battery pack it might be worth simply running the raspberry pi next to the antenna with a very short pigtail. Just for an hour or so and at least get a best case out of what is going on. Heck might want to try a simple cheap magnet mounts antenna that normally comes with usb radios as others have said the metal roof can help with signal strength.
Reading that you are near the coast, you should have a lot of line of sight simply being on the top of the building. It sounds like a cable problem as others have noted. For my own system, being on top of 130ft radio tower, I simply placed the raspberry pi in a NEMA box and powered the whole thing via POE injector as I did not want to deal with signal lost from the length of the cable and ethernet is cheap vs radio cables.
Based on what you have shared, there are three options I can see:
1: Move the receiver and power close to the antenna, with a short cable.
2: Replace the cable with a lower loss cable. Stay with the 50 ohm impedance and avoid right angle connectors if possible, as they do not behave nicely at this frequency.
3: Add an LNA with Bias-T power at the antenna to make up for cable losses. Probably not needed if option 1 or 2 are implemented. Uputronics makes a good filtered LNA for 1090MHz.
Anyone else have ideas and suggestions, or changes to the above?
Are you sure the existing cable and antenna were for ADS-B and not Airband?
Any quality coax will be banded every meter or so - if it’s not, it’s only suitable as a cloths line.
The Gain Graph tells the story - it never drops off max gain. What ever the reason, you don’t have a functional antenna connected to the receiver.
Assuming some of the planes at your airport are transmitting ADS-B, even at low gain, the receiver would be likely to overload.
If you look up this cable on Amazon you will find the 50ft length for $47. I use a 75ft piece of this exact cable running from my Rpi-4b directly to my antenna 30ft in the air. I tested this cable with an analyzer before installing it and the numbers looked great. The length is more than I currently need but I don’t have signal loses that effect my reception. Increasing distance to the horizon with your antenna height is a key component to your success after you have the proper hardware in place.
Derek, Referencing the first message, was the previous receiver at work ADSB or Airband? If Airband at 137MHz, it explains the poor reception at 1090 MHz. All antennas will receive all frequencies, just not as well as the one they are designed for. Good catch on this one geckoVN.
Derek351 You mentioned you had a second antenna. Sounds like it is time to see if the second antenna is the same length as the current antenna and test the second connected to your current system. At this point, the only way to improve is to swap out parts, antenna and cable. Your call on how and when. You are close.
Is that some sort of microwave or other repeater tower that I see peaking up over the steel building roof just to the right of the overhead door in the first photo?
I am about 95% positive that at least one of the two antennas is 1090. The receiver that was in place previously was owned by a company that sells adsb data back to FBO’s.
I did run both antennas simultaneously with two separate pi’s and receivers. There was no difference in performance.
I’m waiting to put a new antenna and cable up, as I may be moving to a different hangar soon. In the interim, I’ll try an LNA to see if that helps.
Good eyes. I’ve been told that’s also part of an ADS-B system for the airport. There are two large server racks in the back of my hangar that it all feeds to. I believe it has some type of V/UHF component to it, but I don’t know if it transmits. Info on the racks leads me to this website: https://passur.com/
