My use of the term was the dictionary definition of nonexistence as used to refer to something “unsubstantial”. Sorry about my language skills.
Just to be difficult, GPS operates below the noise floor 
(but it’s spread spectrum so that’s a bit different)
Hi Oliver
The plot below may be of interest to you.
It is a polar plot of dBm signal strength vs distance of aeroplane for adsb signal at my station (Toronto).
It was very kind of Martin (Flightaware Forum member G8JNJ) to do this plotting for me.
Please see Martin’s post in eHam.net for full details: http://www.eham.net/ehamforum/smf/index.php/topic,38371.msg866912.html#msg866912
Note: the dBm vs color legend is at bottom right of the image.
Interesting stuff.
One thing to watch out for if you are going to mess with the rtlsdr gain is that the gain values are not accurate, that is, the difference between a gain setting of 20 and 30 is not necessarily 10dB. I have a slightly better calibrated version floating around somewhere but it’s still not great.
That sounds about right, In an ideal world or maybe where you have a good high mast to mount the antenna on the maximum path loss will stay well above the noise floor of the ~4db sat amps. The problem comes in with locations like mine where the bottom degree or so to the horrizon (where most of the aircraft are) is looking through trees in most directions so the path loss is much higher and that extra 3db makes a significant difference.
I have 2 of the satellite line amps here that where tried but neither perform as well as the Pga103 based amp.
@obj The Adsb signals fairly spread out, so the next verssion of dump1090_mute will pull signals from below the noise floor ? 
I have seen some of your other photos, how high is the apartment? Anyway it looks like you snuck the mast up well above the trees 
I’m stuck with the antenna (currently a 1/4 wave spider variant) about 8m above sea level.
Yes, I am lucky that my apartment is higher than trees, but also unlucky that it is much lower than the surrounding high rise buildings.
By the way all variants of 1/4 wave antenna are good - simple to make, easy to get right, and sure in performance. Coco and wire collinears are easy to make, but hard to get right, and mostly end up in poor performance.
Yes. I have a fair selection of failed 1090 antennas in the garage at the moment 
including 2 RG6 COCO, 1 RG213 COCO, 3 attempts at coiled wire collinear, 2 x 4 element hairpin collinear and an air insulated 5 element COCO.
So far the successes are the 1/4 waves , PY4ZBZ’s 2 element collinear? and a directional Vivaldi on PCB though i haven’t given up on the air insulated coco.
Yes. I have a fair selection of failed 1090 antennas in the garage at the moment
Me too
Interested in your air insulated CoCo. Any pics?
Has anyone measured (by test equipment) the Gain & SWR of these antennas? or has anyone compared the performance of these antennas with a benchmark antenna of known and confirmed performance?
Please see this post:
http://discussions.flightaware.com/ads-b-flight-tracking-f21/wire-collinears-an-example-of-simulation-software-s-failure-t36358.html
.
I’m away on holidays at the moment so don’t have any decent shots of it with me.
Its built with 136mm (i think) lengths of 6mm ID copper tube and 1.5mm wire for the inner conductor so around 65ohms.
Each section has 3 x 5mm slugs of foam PE from RG6 inserted at intervals to keep the inner conductor centralized, It takes a bit of practice getting it all soldered up without melting the PE slugs! The bottom section has normal unjacketed RG6 through the center and a 1/4 X 21mm wave coaxial ballumn on the outside. I wouldn’t recommend this unless you have the antenna bug bad (which it sounds like you probably do )
My first non shorted version with a 1/2 waveish whip out of the top actually worked quite well until i had to go and try and improve it. Then you probably know the rest… 
For my part the test gear i do have runs out of puff above 400mhz or so, so no.
As for comparisons my 1/4 waves are the reference. I can just “see” the Brisbane > Melbourne air lane with one so its easy to see better performance there. Same goes for planes descending into Sydney from the north, if i can see them without an LNA then it better than the 1/4 wave.
Not exactly the full Scientific method but it works for me. Over Christmas i might set up my spare RPI with 2 dongles, a 1/4 wave for reference and try some direct comparisons. Any thoughts on how best to handle and display the results??
The models you linked look great and the COCO model was a true work of art but i have never had any joy in getting verifiable results from 4nec2 either, at least not at these frequencies, It seems more suited to the HF ham bands than microwaves. I remember a post some where, (maybe hamnet) that pointed out that you have to model the feed line as well to get meaning full results at microwave frequencies. Maybe they had a point.
I built this antenna today, it seems to work quite well. But I have a general question… I had lots of trouble pushing the copper core into the shield, the core would often push through the outer jacket. Any idead how to solve this problem?
Maybe I need another brand of coax with a tougher outer jacket?
I started a pilot hole with an ice pick.
Hi ameins, welcome
The CoCo in the first post of this thread by jepolch was a trial to improve the performance of the CoCo. The 65mm bit shown was to try to tune the antenna. I think most people gave up on it, I certainly did.
Are you trying to make the whole CoCo with 65mm lengths of core? I make the CoCo with 10mm of core exposed which is then pushed between the outer insulation and the shield. I make a “pocket” by temporarily poking a small nail in before trying to get the core pushed in.
What type of coax are you using? There is a requirement to adjust the length of the segments depending on the coax’s velocity factor. You really only need this level of detail if you are trying to push your antenna to the max.
Let us know how you get on.
Use a hair dryer to warm the jacket, then it becomes more pliable and fairly easy.
Dear Zahidul Bhai
Hope doing absolutely fine. I need to get some advice to extend my coverage. I am using ADS-B receiver but coverage is too small competing with other ADS-B receiver. Plz get me you Email so that we can have a chat.
Regards
Md.Maynul Haque
Dear Maynul bhai,
Hope you are doing fine. As per my experience coverage depends on some matter like
#Free open area,
#Shorter length of antenna cable.
#Good quality RF cable & connector.
#Appropriate 1090mhz antenna.
#Low noise high gain ADSB modem.
Etc.
I am not sure about your problems but I will be happy to help you to give you antenna, cable, modem etc. You can reach me at GP 12540076 email zahidulhasa@gmail.com. Or you can give your contact number or e-mail I’d to cooperate directly.
Zahidul Hasan.
First post here. Awesome thread, lots of very smart people!
I had an RPI3 kicking around so putting it to work for Flightaware seemed logical. Super easy to set up.
Tried the factory antenna with the USB dongle which worked… but not great, and -30C I don’t feel like running cable outside.
Then tried an old cell phone antenna with about 30ft of cable (LMR195, I didn’t want to cut since I can use it elsewhere if not working here). Had to shorten the antenna just a bit to match the 1050±MHz. Works much better even with the longer feedline, and positioned it close to a window. Range was around 150NM or so in the window’s direction, west in my case.
Then this am I realized I still have an unused 2.4GHz vertical up on my tower about 60’ up with LMR-400 running into the shack. I connected to this and get an extra 100nm almost 360deg. Much better signals and I can see aircraft landing/taking off within 500’ of the ground at CYWG about 40mi away.
Ordered an ADS-B antenna from Amazon so after it arrives I’ll switch out the 2.4GHz antenna with the new one when it’s warm enough to do some climbing… Hope to see some improvement with a proper antenna.
Best of the season to everyone!
4 Likes