We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale.

Author Topic: A very high antenna for ADS-B Aircraft Transponder Decoding  (Read 1686 times)

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 23698
  • Westminster, MD USA
    • View Profile
    • Black Cat Systems
I just got a new AirSpy SDR, and wanted an improved antenna for receiving 1090 MHz ADS-B aircraft transponder signals. Previously I used a regular VHF/UHF discone antenna, which is mounted on the roof of the house. It worked OK, but not great. I built various specialized ADS-B antennas, such as small ground plane and colinear antennas, but none produced great results. They were all mounted inside the shack, and that was the problem, a lack of height.

I considered putting up a mast, but that was going to be a lot of work and expense. I've got a lot of trees in the yard that I use for HF antennas, certainly I could find a way to make one work for this application. All my HF antennas are hung via ropes shot over tree limbs. This works fine for dipoles, etc, but with a VHF/UHF antenna you want height, as well as being in the clear, away from branches and leaves that can cause significant attenuation at 1090 MHz.

 I then hit upon the idea of finding a way to pivot the antenna up above the branch that the rope is over. I attached the antenna to the end of 20 ft of plastic conduit. The coax runs down the center of the conduit. The rope is attached about one third from what will be the top end of the conduit when it is hanging from the tree. The weight of the lower 2/3 of the conduit, plus the coax, pivots the conduit so it is nearly vertical. This allows it to mostly clear the tree limb. It's not completely above the entire tree, but it is over most of it. And it is about twice as high as the existing discone.  The result is significantly further range and a higher decode rate. Before I was lucky to get 100 nautical miles, now I get 200 nautical miles.  I am getting a peak decode rate of about 1000 frames per second, not bad for a Saturday afternoon. Can't wait to try it on a weekday.

Some photos, the red arrow points to the antenna, which is a small ground plane antenna I threw together in about ten minutes. Just a 2.75" wire mounted on an F connector, which is on a paint can lid as the ground plane. Next I will try making an improved antenna. I also have a discone antenna on order.  I have a pre-amp mounted right at the antenna, to amplify the signal before the 100 ft coax run. None of this is weather proof right now, it is more of an experiment.



« Last Edit: May 26, 2018, 2044 UTC by ChrisSmolinski »
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline lundaym

  • Newbie
  • *
  • Posts: 1
    • View Profile
Re: A very high antenna for ADS-B Aircraft Transponder Decoding
« Reply #1 on: May 27, 2018, 0048 UTC »
Good job, Chris.  That's a superb improvement.  What is your preamp?

I tried to install the antenna and run a USB cable (50 feet) to the SDR Play co-located at the antenna.  I can't seem to get the USB signal to make it through without significant loss.  I must be doing something wrong....

Offline pinto vortando

  • Sr. Member
  • ****
  • Posts: 462
    • View Profile
Re: A very high antenna for ADS-B Aircraft Transponder Decoding
« Reply #2 on: May 27, 2018, 0258 UTC »
Nice work !
With that range, from your QTH, things should start to get interesting about 1700 hrs on weekday evenings.   8)
Das Radiobunker somewhere in Michigan

Offline Token

  • Global Moderator
  • DX Legend
  • *****
  • Posts: 1801
    • View Profile
Re: A very high antenna for ADS-B Aircraft Transponder Decoding
« Reply #3 on: May 27, 2018, 0407 UTC »
I have configured a Pi 3 as streamer for the SDR, then put it at the top of a 200+ foot tower and WiFi'ed it down.  Talk about low loss coax ;)

Also, same basic hardware, but including a patch antenna for the WiFi, I lofted it under my DJI Phantom 4 Pro.  With a Yagi on the ground I got the Phantom up to about 600 feet before I lost signal.   Shhhhh...don't tell the FAA.

Gotten some pretty nice ADS-B ranges out of both those setups.

T!
T!
Mojave Desert, California USA

Offline Josh

  • DX Legend
  • ******
  • Posts: 3307
    • View Profile
Re: A very high antenna for ADS-B Aircraft Transponder Decoding
« Reply #4 on: May 27, 2018, 1554 UTC »
Put the collinear up there and see how that fares.
Conveniently located near Vincennes Indiana.

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 23698
  • Westminster, MD USA
    • View Profile
    • Black Cat Systems
Re: A very high antenna for ADS-B Aircraft Transponder Decoding
« Reply #5 on: May 27, 2018, 1735 UTC »
Put the collinear up there and see how that fares.

I've had dismal results with collinears, as have many who try them. They work better on paper than in reality, unless you have the proper test equipment. Height seems to win over antenna design  ;D

I managed to get the antenna a little higher, using two 8 ft long pieces of 1x2 wood, which is a little lighter and less prone to bending than the conduit:

« Last Edit: May 27, 2018, 1800 UTC by ChrisSmolinski »
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 23698
  • Westminster, MD USA
    • View Profile
    • Black Cat Systems
Re: A very high antenna for ADS-B Aircraft Transponder Decoding
« Reply #6 on: May 28, 2018, 1649 UTC »
I ran across a very interesting site: http://www.heywhatsthat.com/

You enter in your location, as well as the height of your antenna, and it will produce a map showing what the line of sight range is, for two flight levels, taking into account local terrain (hills, mountains, etc).

Below is a map for my location, assuming a 65 ft high antenna. The orange line marks the 10,000 ft flight level, blue is 40,000 ft. The general shape and extent roughly matches what I observe from ADS-B positions, I don't get quite as far as the blue line, but close. Plus most planes are well below 40,000 ft.

Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline ThaDood

  • Sr. Member
  • ****
  • Posts: 306
  • There
    • View Profile
    • Extreme Part #15!
    • Email
Re: A very high antenna for ADS-B Aircraft Transponder Decoding
« Reply #7 on: May 29, 2018, 0313 UTC »
Interesting pattern. You must be in a valley that looks NE and SW. Contemplating that due to the null you have going towards NWPA and WNY, and the opposite direction towards the ocean, which you'd think would be the greatest range. As far as antennas go? A 1/4-wave GND-plane for 1294.500 FM Simplex (The 23cm band.), may also work well. Heck, make one out of a female, chassis mount, N-Connector and solder on 14AWG solid copper wire, bare. Maybe make the elements about 1/4 inch longer for better matching. One thing about 1GHz, and higher, is the line loss really sucks, so the idea of a mast mount preamp is a must for sure. Even LMR-400 will be more than -3dB at 100ft. Passing thoughts, but sounds like you are on the right track here. The F-connector is good, since down converted Ku and C band satellite FREQ's at 950MHz - 1050MHz uses F-connectors as the standard still.
I can't decide upon what's worst, young and stupid, or old and chemically dumbed down.

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 23698
  • Westminster, MD USA
    • View Profile
    • Black Cat Systems
Re: A very high antenna for ADS-B Aircraft Transponder Decoding
« Reply #8 on: May 29, 2018, 1206 UTC »
Interesting pattern. You must be in a valley that looks NE and SW. Contemplating that due to the null you have going towards NWPA and WNY, and the opposite direction towards the ocean, which you'd think would be the greatest range. As far as antennas go? A 1/4-wave GND-plane for 1294.500 FM Simplex (The 23cm band.), may also work well. Heck, make one out of a female, chassis mount, N-Connector and solder on 14AWG solid copper wire, bare. Maybe make the elements about 1/4 inch longer for better matching. One thing about 1GHz, and higher, is the line loss really sucks, so the idea of a mast mount preamp is a must for sure. Even LMR-400 will be more than -3dB at 100ft. Passing thoughts, but sounds like you are on the right track here. The F-connector is good, since down converted Ku and C band satellite FREQ's at 950MHz - 1050MHz uses F-connectors as the standard still.


Yes, I am in a little of a valley, and there are the tall trees to contend with as well.  This simple 1/4 wave ground plane is working very well, especially considering how simple it is.   RG-6 is low loss at 1090 MHz as you noted, and it's cheap  ;D  I'd like to find something comparably low loss but thinner and lighter in weight (those requirements may be mutually exclusive).

I configured Virtual Radar Server to generate a range plot, it is very similar in shape to the estimated range plot above, with lots of little notches either due to trees or perhaps places where planes have not been observed. You can follow them on the map in real time and see how most of them do stick to routes.

Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline Josh

  • DX Legend
  • ******
  • Posts: 3307
    • View Profile
Re: A very high antenna for ADS-B Aircraft Transponder Decoding
« Reply #9 on: May 29, 2018, 1723 UTC »
The freqs above 1GHz and the requisite feed line to get the system up in the air are the only reasons I consider remoting a rx and mini pc thingy, then wifi the take down to the decode computer.
Conveniently located near Vincennes Indiana.