Homemade ADS-B Collinear Antenna

12 comments

  1. Laszlo Lebrun

    I just wanted to add a consideration, that I haven’t found in many blogs about colinear antennas built out of coaxial cable. In fact the velocity of the signal is different, whether it uses the inner or the outer part of the coaxial cable, theoretically requiring different lengths for a half wave match. Since however the interaction is highly symmetric, one cannot just make the odds parts of the antenna shorter, or vice versa. So the best solution is a compromise and involves the usage of high velocity coaxial cable for the antenna part to reduce the differences, especially if you want to make an antenna with more than 6 to 8 sections.
    If you want a good antenna, it would have been a good idea to invest in a few meters of high-end coax cable (which has a velocity >75), and if you can afford, use it for the transmission line as well since high velocity usually peers with low losses.

  2. Spongella

    After seeing this YouTube video I decided to construct one of these collinear antennas using RG/6 with a total of 10 elements. The antenna is about 18 feet off the ground. I can receive ADS-B signals as far away as 350Km while with my former antenna, a broadband Spider Procomm I was able to receive aircraft as far away as 125Km, so the collinear definitely is an improvement. I’ve also used it on lower frequencies, such as the NOAA weather channels on 162.4 – 162.55 MHz and it works well.

    I would like to thank the individual who produced this video for disseminating this information to the public, it’s definitely a superb antenna.

  3. Alex

    I bult a 16 element antenna (2 meter tube) but I get much better signal with the TV bunny ears. I wonder what could be the problem? I tried with connected and disconnected inner and outer conductors at the top but there’s no difference.

  4. N2JTX

    I am going to have to make myself one of these. I already have some RG-6 quad shield that I can use along with PVC end caps. Just need an F-61 panel connector and some 22mm PVC tubing. I have wondered if using heat shrink tubing at the joints instead of tape might be a better option if it will be encapsulated in a pipe. I do not have to worry about the pieces being pulled apart. Tape is definitely cheaper!

    • admin

      I reckon glue lined heat shrink tubing would work well. I’ve built a few myself at found that hot weather caused the glue on the electrical tape I used to melt and slip. I think heat shrink glue should have a higher melting point than the weather can provide.

      • N2JTX

        I am going to give that a try. My fear, as you observed, is the glue on the electrical tape would melt. Granted having the antenna inside a PVC pipe would protect it but I I like firm connections! I am focusing on building a 12-element antenna. 1/2 inch PVC pipe is readily available in the home improvement stores. I do want to try and put an F-61 panel jack on one end to which I can attach a waterproof F-59 connector and cable rather than hardwire fixed length of cable to the antenna. Once I get this sorted out, I’ll post the results. The paid job still takes priority hi-hi.

        • N2JTX

          I finally had a chance to build this antenna using RG-6 quad shield cable. The manufacturer said the velocity factor was 85% and I used that value resulting in 116mm segments. I built it using 12 elements. After construction, I tested it and I was receiving aircraft and was generally pleased with the results. A neighbor who works as an electronics tech for a large multinational corporation offered to take the antenna to his lab and hook it up to their USD$250K analyzer. The results were less than spectacular with very slight gain in the 900MHz region. Then using parts from his corporate inventory, he built a small 1/4 wave ground plane using an 8 inch square machined aluminum plate as the ground plane, an N connector in the center with a small Teflon covered stub for the antenna. He tuned it to 1090MHz using the analyzer which showed an 8dB gain and gave it to me to test. The results are incredible. Where I was lucky to get 100 frames per second in ADSB#, I am now seeing over 300fps at times. I am seeing aircraft out 120nmi. All without an amplifier and using some low quality RG-59 coax for the feed. I am tabling the collinear project and I am going to look to get two of these 1/4 wave antennas for myself (I have two monitoring locations). I cannot imagine what further improvements can be made at this point since 120nmi would be just about at the horizon for an aircraft at 30000 feet.

          • admin

            Interesting to hear your results. When I built my own I found the antenna performance actually got worse once i’d gone over 8 elements.

            I’m not quite understanding how the ground plane gets 8dB gain though. What measurement is the 8dB in respect to? I thought a 1/4 groundplane was a 0 dBd gain antenna.

            • N2JTX

              The 8dB gain I was quoted has me puzzled too since I too was under the impression a 1/4 has 0dB gain. I will have to ask for a copy of the analyzer output. I have a copy of the one for the collinear I built and there is just a slight increase in sensitivity in the 900MHz range. I have an analyzer output that was also generated for a commercial 922MHz antenna just for practice which I can reference as an example of a good antenna. It is pretty much strait line until about 860MHz and suddenly jumps in gain peeking at 3dB around 922MHz. It then drops off again as the analyzer went up to 2.1GHz. As I noted in my post, this 1/4 wave antenna has a ground plane made of a solid machined sheet aluminum square plate about 8 inches on each side. Those dimensions are larger than a 1/4 wave at 1090MHz and may be providing gain. The plate is closer to a 1/2 wave than 1/4 wave. I only have the antenna for the weekend and have to give it back so hopefully it can go back to the lab and get a plot generated. All I can say for certain is the amount of air traffic I am seeing now is incredible. The furthest distance I have measured so far is a plane 129.65nmi from me at 37000 feet. A modified version of ADSB# that I created to record the peak frame rate recorded 424 fps at one point. I never saw anything above 120 fps using a wideband scanner antenna that goes to about 1GHz.

              I have to admit having “toys” like that analyzer are great for antenna design work. Eliminates all the guessing. I do not know the model of the analyzer but it made by Rohde & Schwarz.

  5. Pathogen

    So I ended up making this today. It ended up being so great I replaced my 4 foot dipole for sdr. The p25 traffic I listen to in 830’s is gorgeous. My ADSB reciever now works as far as 150NM. Thanks for sharing!

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