A good surprise from a cheap antenna!


#1

(TL;DR: If you’re running PiAware indoors, using a full-wave antenna may give you a really nice bump in signal quality)

I’m running PiAware for almost 8 months (and had a perfect streak until my SON UNPLUGGED THE &^% THING while I was out of town.) I’m in an indoor setting, a window that faces SW with a decent sky view, and I’m in one of the approach routes for IAH.

Was seeing lots of close-by traffic, but anything over 50 miles was pretty much a few blips and it would drop off. After looking at some of the ingenious setups here (I know when I am among my betters when it comes to understanding RF), I wanted more. But I am hesitant to take the step of an outdoor penetration (leakage, sealing, and electrical concerns).

Was using the little antenna that came (I think) with the PiAware stick (about 6 inches, with a coil at the bottom, magnetic base).

I read just enough about antennas to pick up that the ratio of the antenna length to wavelength is important. Look again at 6-inch antenna, which is a little more than a half-wave. Look at the dinky little extendable antenna I got with another SDR dongle, notice they have the same connector…

I extended it to just under 11 inches, taped it in place on the window frame, and went downstairs to see if I had trashed it. Quite the opposite, and here’s the results. I swapped antennas about 10PM CDT on the 26th. Immediately saw a HUGE increase in number of positions/sec. :open_mouth:

After 24 hours, I can say that I am not seeing a lot more aircraft than I was before, but I am getting a whole lot more positions from them. Flights that dropped off after 40 NM now give consistent readings for almost twice that, and I’m seeing a lot of traffic to the E and N - which has to come through the roof.

Since I live in an area with extremely dense air traffic, I think there’s probably more value to being able to give solid positions on the many flights close by, and not worry too much about getting more range.

I’m curious, does anyone know at how many positions/sec a PI3 can reliably handle? (Bonus: How much of a hit does that number take if you’ve got a single machine looking at the local PiAware data page?)


#2

Take some pictures, if possible of the antenna and after I saw your location, I am north west of you in Killeen Texas.


#3

(1) Trial Run Results for Three Types of Whip Antennas

(2) Trial Run Results for Four Sizes of Ground Planes

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#4

Up to 200 nm from this indoor antenna. Removeable part of whip cut to 52mm

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Circles: 1st 100nm, 2nd 150nm, 3rd 200nm, 4th 250nm


#5

I think the max is around 1.600msg/s. Not every message has position information.

Edit:

Quote from a ICAO DOC 9224

“The ADS-B information is broadcast in separate messages, each of which contains a related set of information (e.g. airborne position and pressure altitude, surface position, velocity, aircraft ID and type, emergency information). Position and velocity are transmitted twice per second. Aircraft ID is transmitted every 5 seconds.”


#6

Thanks - I don’t think I’ve seen (even with my new, super-improved rabbit-ear) more than about 240 messages/sec at the busiest part of the day.

I’ve got four different Pi’s around here that I’m using for various things, and I’m still absolutely amazed that piece of hardware that costs so little has more “oomph” than what I considered a high-end unix server 20-ish years ago.


#7

My wife is very patient about putting up with some of the mess from my various hobbies. But she’s out of town for the night. I’m pretty sure there’s a pizza pan in the kitchen that could see what affect a ground plane has. Does it need to be a ferrous metal? I’m thinking no, but… Clearly research is needed.

Will post results!


#8

A Pizzapantenna, that would be a new one :grin: