Glass attenuates the 1090 MHz signal. Wood blocks it less.
For details of attenuation, please see this post:
RF Signal Loss in Penetrating a Building
In my case the roof is made of clay tiles and some insulation, (and the walls are solid red brick masonry).
In this case, I guess being close to a single glazed window is still an advantage, but only for the reception in this direction, and a disadavante for the reception in all other.
Being close to the top reduces the distance to the tow sides of the roof, which should also reduce the signal loss. In sum, this seems to be the best option.
It is like a triangle, if you move to the left or right hand corner, you increase the distance to the other side, only if you move upwards to the top, the distance to the left and right are reduced.
Thank you for the heads-up on that thread. I hadn’t come across it yet. No doubt it will come in useful!
Folks,
After a couple of weeks running this antenna I would like to see how it performs for you too.
I started this thread http://discussions.flightaware.com/ads-b-flight-tracking-f21/disappointing-results-with-my-setup-what-s-wrong-t38177.html after some unsucessful atemps with the Coaxial Collinear and after some research found the antenna I would like to share here.
I’s a J-Pole Collinear, an easy to build and tune antenna.
Here is its diagram and 1090Mhz lengths
Wire: 16 AWG copper (enameled if available)
Coils: 16 turns of 5mm inner diameter 53mm long
(you can build with 2 to 4 elements (1 to 3 coils)
The feed line should be connected at 6mm from the bottom (shield to the short element, as per this image).
If anyone is interested in building it please let me know and I’ll update the needed details.
EDIT: Updated dimensions to reflect new tests.
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what size wire did you use for this?
–bob k6rtm
Ops, sorry, 16AWG enamelled copper
Just about to make your antenna.
I have a question for the experts. I have the orange Pro-stick on my test system which is currently connected to a 6 element CoCo. The J pole is a “shorted” antenna. Do I need a DC blocker to make sure the amp in the Pro-stick doesn’t fry?
You dont need dc blocking for the ProStick. It’s only needed for tee bias sat amplifiers
I’ve tested both, currently I’m using a 20dB amp with a std rtlsdr stick
Thanks, the antenna is on test.
I only had 1mm wire so built it to your dimensions.
How many elements did you make?
Just the one coil for now.
I believe the 2 elements will perforform something around 30% more messages than a 1/4 ground plane, not that great.
Preliminary results show the Collinear J pole is not as good as my 9 element CoCo. I will add another 2 elements tomorrow.
https://serving.photos.photobox.com/3728202979e367abc2646b1fd9c5d7274eddf305bb3dfa6d8ea6e1ae5602b394af52130e.jpghttps://serving.photos.photobox.com/201360458fe98ffece05641d97445b8b22e5ed4cd8113236a7f4d3b0a516a9b860f5be99.jpghttps://serving.photos.photobox.com/109836645ae779ee02faeb175e3d0f35419b1217b78d987468cb623da28ea6fc7116855d.jpg
Here is my CoCo for comparison
What is the length of the wire used to make the coil? Is it half wavelength or something else?
Fairly good results, 70% of the message rate of a 4 elements CoCo
This article trys to explain the black magic behind these antennas and was the main source of my findings. Search for a section named “Wire length in Collinear J-Pole Phasing Coil”
hamradio.me/antennas/improvi … per-j.html
I’ve tested 18turns / 60mm and the gain decreased significantly, meaning poorer SWR. Will try another sizes to see if is there any improvement, but so far this was the best results I got.
I’ve actually got a reel of 16SWG tinned copper wire on the way so I’ll have a go at that in the next week or so. I already have a reel of 18SWG enamelled copper wire but I really hate stripping the enamel off of it so I’ll wait until the other stuff turns up just because I prefer it.
I know the 18SWG is a closer match to 16AWG but it’ll be interesting to see how it performs.
/edit - Stuff it, I built one using the 18SWG enamelled copper wire because it’s a new aerial to try and having got 35 years of aerial building and experimentation behind me, I wanted to do it!
Exactly as per the plan, double and triple checked everything.
In my back bedroom I’ve got a Pi3 with an FA Pro Stick Plus in the top with a quarter wave ground plane spider with eight radials. I removed the spider, plugged this aerial in and watched my aircraft count drop from 69 to 40 (it’s late in the evening here, there’s not much traffic). Plugged the spider back in and the count went back up.
I wish my VNA went up to 1GHz, it would make this aerial building lark so much easier. I’m normally doing stuff for HF.
Reading the url you posted above, is the author, John Huggins, saying that it doesn’t matter how much wire is in the phasing coil but the distance between the “radiating” elements (53mm) is the important factor?
Would you mind sharing a picture of your assembly? Specially the feed point? This is a very directional antenna (around 7dB for 4 elements, 6dB for 3), not the best for indoors thou
That’s what I understood too, and both simulations on 4nec2 and pratical results says the same.
Here is my 3 elements I replaced by a 4 elements this weekend.
I should have quadruple checked everything - I did make a slight error in construction, I woke up this morning with the flash of realisation. I could try and modify what I’ve done but it’ll be messy so I’m going to rebuild it later this week.
I made a new Collinear J pole today with 4 elements. It performed OK but still not as good as my 9 element CoCo.
I then made another 4 element one but with the elements 137.5mm rather than 132mm. Still kept the phasing stubs at 16 turns and 53mm height. All made out of 1mm copper wire. 137.5 is half wavelength I calculated 
Worked a treat !!
The max range of the J pole is about 20nm less than the CoCo. 190nm vs 170nm
Tomorrow I’ll remake the bottom end of the antenna with the quarter wave stub at 68mm and the three quarter stub at 206mm keeping the tap at 6mm.