I’m in an apartment building about 250ft high, and I have line of sight to KSFO and KOAK which are 12nm and 5nm away from me respectively. I’ve been reading about folks who get 100+nm of range, but I think the furthest out I’ve seen have been ~40nm and that might only be one position reported!
I feel like given the vantage point I should be tracking aircraft quite some distance out, but I’m also in a noisy urban RF environment – so maybe this is as good as it will get? I’m kinda out of big ideas for increasing range! I’d love to hear feedback from the FA community on whether I can squeeze more out of this setup!
Setup
I’ve done a fair bit of research and slowly added components based on recommendations read here and elsewhere. The current setup looks like this (in this order):
I placed it right against the windowpane because of one unfortunate incident involving lowering the blinds which cause the antennae which caused much sadness. The tradeoff of neighbors thinking I’m an NSA spook is well worth it:
You can see I’ve even gone as far as throwing some ferrite chokes on the various cables. Actually having the antennae pressed against the glass was also intended to help with line of sight, in case some of the metal framing components of the windows were giving me dead zones.
You might also notice the great big AT&T building bristling with RF gear right next door
Software wise, I’ve left dump1090-fa gathering with AGC on, absolutely out of the box so far. It occasionally hunts down a few steps but typically returns to 51dB (before this, I’ve done a ton of experimentation with a HackRF One but I’ll leave that aside for now)
Remaining ideas
Maybe …
… I’ve got the setup in the wrong order? I read conflicting things about the order of LNA and BPF
… the LNA or BPF are backwards? Because power is involved (albeit in tiny quantities) I didn’t want to experiment needlessly and damage any components
… the Nooelec sucks?
… the reflective coating on the glass contains something inhospitable to RF? I think dangling the antennae isn’t an option, to paraphrase Louis in Ghostbusters “the superintendent would be pissed”
… the noise of the area is too great?
… proximity to airports means weaker signals are drowned?
… the dual band filter is not helping and I should have gone for the single band 1090?
I would say, most likely, yes.
Try the BPF before the LNA.
The LNA you are using is wide band and because of your proximity to a potentially large source of wide band emissions you will most likely be generating intermodulation products within the LNA which would be reduced by putting the filter between the antenna and the LNA.
Thanks, @LawrenceHill , I’ll try swapping the positions of the LNA and the BPF.
Dumb question, but I have the orientation of the LNA such that the end marked “Input / DC” is connected to the antennae, while the end marked “Output / Power LED” is connected (currently) to the BPF. That’s correct, I hope?
Could there be some kind of UV coating/film that’s blocking incoming RF? I experienced this in my old job where I had tried to use my scanner (BCD436) sitting on the windowsill. Anything 800mHz or higher was dead. I’d step outside (20ft away) and those systems would light up perfectly. Just an thought…
Smart XTR. NooElec say they don’t recommend this one for ADS-B as there’s “a small gap in frequency capability near 1100MHz. As such, we do NOT recommend this device for ADS-B usage.”
Update – trying a FlightAware Pro stick with a FlightAware 1090Mhz only filter. Removed the NooElec LNA.
Only had it running for an hour or so – but absolutely no change in range as yet. AGC is on (i.e. default config) and it dropped the gain to 49.6 dB and has stayed there.
Here’s a snapshot of tar1090 with some extra columns turned on. Not much action!
Seems like the trails are quite broken up outside of about 5nm. I want to fiddle with the gain but I’m going to let AGC do its thing and see what happens first.
Over the weekend I’ll try taking the setup up to the roof, and see what happens when taken outside. And maybe just dangle it out the window to get another data point.
Here’s a comparison of tar1090 and globe.adsbexchange.com at the same time. I really only have a line-of-sight view to the west and to the south, but that view includes KSFO and KOAK …
I can barely stop laughing enough to type. Holy crap.
Ok so … next question … anyone got suggestions for discreet antennae I could mount on the outside of the building?! It would have to have a coax connection thin enough to squeeze through the weather proofing. As you can see by how far that window opens, the building isn’t going to make this easy.
@abcd567 has some discrete antenna designs. Since your windows seem to have a metal film inside the window, try to keep the antenna away from the window or frame surface. At least 69 mm /2.75 inches away. Others here will have some good ideas I am sure. Have Fun.
An airspy may help. It has a much wider dynamic range so allows you to run an amplifier(LNA) at a higher gain setting compared to an FA or nooelec dongle. It could receive more and less powerful signals compared to the FA or nooelec Dongles.
Looking at your range stats, I think I had that much range when I had a small antenna on my basement window guards(About 3 feet off the ground).
I also see a lot of Microware antennas on the building in the photo. You may need a better filter, something like a cavity filter, to block out their noise.
Bog standard government issue empty toilet roll – keeps the antennae separated from the building while not flapping around in the breeze drawing attention. Also light enough to not become a projectile should it depart connection with the building and the coax cable …
@astrodeveloper based on the size of the FA antennae, I don’t think I could plausibly sneak it out the window without drawing attention from nosey neighbors or building guests visiting the roof area. Window trim material is aluminum so magnets are off the table. So I decided to try the PCB antennae which had some pretty positive reviews. RG316 was definitely the right kind of cable, with some careful routing it worked a treat – thank you for the suggestions!
Results:
Still fiddling with gain settings (this antennae feels quite different) but over the past few hours, not unusual to see aircraft at +200nm!
The antennae feels very sensitive to the distance between the PCB and the window frame. Is this to do with ground planes? Not something I understand whatsoever at the moment. The toilet roll was orders of magnitude better than letting the PCB sit too close to the aluminum, although it seemed the further out the more reception improved. @astrodeveloper is this what you were referring to with the 69mm requirement?
Weatherproofing, or complete and utter lack thereof. It wouldn’t be too hard to make a proper enclosure, but for now I might try a ziploc bag. Winds can get gusty up this high – 75 mph when a good front is moving through – so I think weather and wind proofing is going to be a challenge.
Thanks all for the suggestions and feedback! I would like to end up in a place where I have a weather and wind proof setup that remains discreet enough to avoid attention while still providing great ADS-B data. Seems like I’m very close, and it has been a lot of fun iterating on the solution.
One other RF related question – I’ve noticed that very distant signals are dramatically improved if I simply touch the RG316 cable fairly close to the SMA connector. Take my finger off - signal disappears. Touch it again - signal returns.
What electrical property might be causing this? Simply acting as a ground connection? Why might that improve a signal?
As a control test, have you tried putting the FA antenna against a wall (i.e. not a window) to see what results you get? Thickness and composition of the walls will determine what you see, but it could be worth 30 minutes of your time to see what, if any, differences there are between the materials in the window and the outer walls. Move the antenna around a bit to see if there is a “sweet spot” in the wall. A long shot yes, but an easy thing to do to understand how your environment affects your reception.
Space is very constrained – the window is ~260ft off the ground so it opens barely enough to get my forearm out. It’s in the center of the building and the entire construction is glass and aluminum. So, alas, there’s no real exterior wall to perform this test. But I did see dramatic fluctuations moving the antennae around outside – the main challenge will be securing the antennae afterwards. Also as noted, having my hand touching the RF cable seems to alter the reception quite a bit.
I did do some testing on the interior walls with the reasoning that whatever RF hostile coating was on the glass might not be present in as high a quantity. And that was indeed the case – inside the building, laying the antennae flat on the floor beneath the window got better reception than the antennae positioned vertically in the window.
I like the “Bog standard government issue empty toilet roll” spacer idea. Any metal near an antenna changes the ability to receive signals. 69 mm, is 1/4 wavelength of the 1090MHz frequency.
Because you are in a glass/metal building and not implementing the move my location option, moving the antenna around to slightly different locations is a good idea. Antenna positions are often one of those “whatever seems to work” concepts. There are no perfect locations, just one that gives you acceptable results. We all play with our antennas, cables, filters, and tweak software and hardware. It is part of the fun in this hobby. Enjoy, and great idea again on the antenna mount.
As far as touching the cable, it likely changes the antenna resonance / impedance at the ADSB frequency. You became part of the antenna. Us old guys are reminded when we had to adjust the rabbit ears on our old '50’s televisions. Always seemed best when one of us kids held the end of the rabbit ear antennas.
In theory, there is little difference between theory and reality. In reality, they can be totally different and often are.
