Drop in positions after Pi update and moving antenna

FlightAware ADS-B Flight Tracking
1

General setup:

image

Several days ago, I moved my antenna and Pi to a new location about a half mile away from the original location, with the intention of giving the setup a better view to the sky. In particular, the original location had a building directly to the west which I felt blocked most of the traffic in that direction.

To my surprise, while my aircraft count has remained roughly the same, my position count has dropped off by 40 to 50%! Besides location, two things changed:

  • The antenna was mounted on a metal roof originally, with the small magnet on the base of the antenna keeping it upright. It is now mounted on regular wooden roof with some PVC pipe raising it about two feet above roof level.

  • Perhaps absentmindedly, I did an apt-get update and upgrade on the Pi as it hadn’t been done in a while, but this may have been a mistake to do simultaneously with the move as now I can’t determine if the update affected something.

I think my gain is set just about right, my RSSI values generally look something like this:

image

My /run/dump1090-fa/stats.json looks like this:

"total":{"start":1723336531.9,"end":1723499732.0,"local":{"samples_processed":386838953984,"samples_dropped":3276800,"modeac":0,"modes":3046026461,"bad":2681007920,"unknown_icao":1296714762,"accepted":[1555314,617584],"signal":-2.9,"noise":-12.2,"peak_signal":-0.6,"strong_signals":1301067,"gain_db":58.6},"remote":{"modeac":0,"modes":6954,"bad":0,"unknown_icao":0,"accepted":[6954,0]},"cpr":{"surface":9572,"airborne":296946,"global_ok":261620,"global_bad":22,"global_range":0,"global_speed":21,"global_skipped":1366,"local_ok":33544,"local_aircraft_relative":0,"local_receiver_relative":0,"local_skipped":11332,"local_range":2,"local_speed":151,"filtered":0},"altitude_suppressed":0,"cpu":{"demod":23769611,"reader":4213496,"background":1173433},"tracks":{"all":10924,"single_message":7641,"unreliable":8184},"messages":2179852,"messages_by_df":[469760,0,0,0,275055,31255,0,0,0,0,0,576188,0,0,0,0,4037,808286,13707,0,1277,287,0,0,0,0,0,0,0,0,0,0]}

Could this be as simple as a loose connection related to the move? Any help is appreciated. I’m pretty functional in the terminal and can dig for more information if I know where to look. Thank you!

2

Your noise level seems really high.
Maybe there is something generating noise at your new location.

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3

If it’s a magnet base antenna (you should probably think about upgrading to a better antenna, but…) moving it from a metal roof to a wood roof likely eliminated the “ground plane”. Try to find a lid from a cookie tin, or a paint can, or something that is flat, metal, and 8, 10,12 inches in diameter. Stick that to the magnet on the bottom & see if your numbers improve.

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4

With that type of antenna, it needs a “ground plane”, (think “reflector”) for that antenna to work. The metal roof that it was on provided the “reflector”.

You can put any type of metal that the magnet mount antenna will stick to too work.
A cheap steel cookie sheet, steel pie pan, etc. The metal “reflector” should be at least twice the width as the height of the antenna for a 360 degree reflection to the antenna. i.e., 5" antenna, reflector 10".
1090 Mhz signals from airplanes will bounce off of solid objects, such as a building, so take that in consideration also.
Good Luck!!!

KB4ERT

5

No.
Reduce gain.

Weakest RSSI in the list at -30 is a good rough estimate for sensible gain.

6

Thank you to everyone for the responses. This is all very helpful.

Upgrading the antenna is actually in the cards (I’m looking at the 66 cm antenna that seems to have wide approval) - but does having the better antenna completely negate the need for the ground plane, or is the ground plane always helpful?

Thanks for that. I guess I need to better understand RSSI. I was looking at this post from several years ago and trying to compare it to what I’ve got going on. I’m going to try going down to 50 on the gain and seeing what happens.

7

I admit that I am a little fuzzy on the theory on this, but my understanding is that it depends a little on antenna length vs wavelength. The ground plane acts as a reflector, so if your antenna length is 1/4 wave, or 1/2 wave the ground plane can reflect the other “half” back to the receiving part of the antenna. (I might have just made that up, but I don’t think so). The longer antennas can receive the full signal wave.

Happy to be corrected if I’m wrong, but I believe it to be something close to that.

On my own site, I went from a mag-mount antenna with the spiral part at the base to the same antenna with a cookie tin under it, to a shortened (1/4 wave) version of the same one, to a 26" FlightAware antenna dangling in a window, to the same FA antenna mounted on my roof and saw a measurable increase in performance with each change.

8

1/4 wave needs a ground plane to work properly, other antenna usually don’t unless they’re designed with it.

There was a thread here adding thin aluminium dishes to the bottom of FA antennas and it helped for more than one person.
But if that’s really a ground plane effect or rather some sort of shielding of signals from below is hard to say.
I’m in the camp that it has something to do with noise coming from below in the house and being blocked by the dish.

I’m a fan of the vinnant 5 antennas, they do come with radials which are a type of ground plane.

Generally you would only add an extra ground plane to the magnet base antennas as they are expected to be set on a metallic surface. (magnet and all)
But as it has proven effective for some people (i believe they were all running the antenna in the attic), so … can always add something.
But yeah i wouldn’t add a groundplane to a nice outdoor antenna especially when it’s outside.

9

All of that is great information, thank you.

I did adjust the gain down to 50 last night, and saw a substantial improvement in RSSI and positions reported almost immediately. I might take it another smaller notch down. And order the bigger antenna. I’ll update the thread when I’m able to see what the new antenna does.

Thanks again!

10

What brand antenna are you looking at? As mentioned above, the Vinnant antennas are a great choice. I have their CC1090/8-P model antenna and I am very pleased with it.

11

I guess one other thing worth mentioning is that, being just two miles from PDX (Portland International) - I get swamped by arriving, departing, and ground.

I get almost nothing outside a 50 mi radius, and probably most of what I get is within 25 mi. This was the case even at the antenna’s old location. I’m hoping that the longer antenna will help this, but I have seen in other places on the forum that being close to a big airport can really impact overall range.

I was looking closely at this one, which is currently not available through Amazon, but similar antennae are available elsewhere. I’m totally open to suggestions.

12

That’s pretty much the same antenna that is in my closet now after having replaced it with the superior performing Vinnant antenna.

13

This is good to understand: https://github.com/wiedehopf/tar1090?tab=readme-ov-file#heywhatsthatcom-range-outline

Apart from that, can of course be noise caused by out of band interference for which a filter will help.
FA filter sadly is pretty expensive nowadays.
This filter is a bit more lossy but it should still get you 150 nmi if you’re having interference issues: https://www.amazon.com/ADSBexchange-com-1090-Mhz-Saw-Filter/dp/B09RPKHQ6S

Why would you link amazon canada when you’re in Portland, color me confused! :slight_smile:

US antenna options:
https://www.amazon.com/ADSBexchange-5-5dBi-N-Type-Female-Antenna/dp/B089Q4BVCB
https://store.adsbexchange.com/collections/frontpage/products/5-5dbi-1090-978-antenna
https://dpdproductions.com/products/ads-b-vertical-outdoor-base-antenna?_pos=3&_sid=f021e1831&_ss=r

14

Here’s the link to the Vinnant webshop and the suggested antenna

Shipping cost are calculated when you check the item out in the webshop based on your address. As long as you can order the item it is in stock and shipped to your destination.

15

If you had a good arm, you could throw a stone from Portland, Oregon to Vancover, Canada. Portland probably stocks Molson Canadian beer in the local stores.

16

One of the guys with Attic Antennas. In my experience from satellite operations and antenna work, a ground plane will improve most any vertical antenna. Antenna theory implies it is mostly relevant to 1/4 wavelength antennas, and not much for longer antennas. My experience tells me it helps most every vertical antenna I have ever used, from ham bands in HF, VHF, and UHF at 1090 MHz. The ground plane does not need to be fancy, just electrically conductive, electrically connected at the antenna bottom and stiff enough for the local conditions. Stiff enough to survive wind conditions if necessary (pie plate, foil, container lid). In the attic, I used a cardboard flat covered with Aluminum foil and tightened up to the antenna base by a nut on the N connector.

The FlightAware 66cm antenna comes with the extra nut at the top of the connector. Thinking about how this works, and the physics behind the antenna theory, the ground plane adds to the received signal for the lowest 1/4 wave antenna portion, and likely lowers the antenna reception pattern to help receive signals at max range. In my cases, on two different antennas, Message Counts increased 3 to 5% (slight graphs improvement), Max Range and plane count increased too. I do not have specific graphs showing the details. No guarantees, just an experimental part of this hobby. Have fun.

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17

Great suggestions for antennas, I will check them all out.

And wow, I completely forgot to point out that I have the blue FA filter: Band Pass Signal Filter, Dual 978-1090 MHz Ă— 1. Any antenna that I get either has to connect to that, or otherwise obviate the need for a band pass filter.

For $170 I better pickup UFOs!

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18

There’s definitely more to see in that area! I’m in Battle Ground & average 800-900 aircraft/day in the winter and 1200-1400/day when the weather is nice in the summer (like now).

My antenna is 282 feet above sea level (3 feet above the peak of my roof) with a clear view in all directions.

I regularly pick up flights at the Canadian border and as far south as Medford, maybe 50 miles offshore (mostly Hawaii flights), and east to Yakima/Bend-ish.

I have the FlightAware 26" antenna on my roof peak as mentioned, 50 feet of good quality cable to reach my garage, the same FA filter as you, a cheap Chinese amplifier from Amazon, and the blue FA ProStick receiver. All plugged into a Pi 3B+ that has been running faithfully for almost 5 years without a break (1753 day streak)

2 miles from PDX could be a blessing or a curse, depending on which direction. If it’s east or west of the airport you will lose a lot of range to the north due to Vancouver Heights…

19

For sure! In the middle of the day I ought to be doing better than this:

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image553Ă—563 42.3 KB

The antenna is just about directly south of the airport off NE 42nd. I’ve dropped the gain to 30 and am definitely getting more positions, they are all within 50 mi though. I wonder if an amplifier in addition to the new antenna will help with the range.

RSSI values are looking closer to what @wiedehopf suggested:

image

Thank you everyone! I’ll continue to update as I play with this some more.

20

What do you look like out to 200 nmiles there?