ADS-B DIY Antenna

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giacomo1989

Member
I've build my ADSB collinear antenna with 6 coaxial elements and it's doing a great job, over 100nm of coverage and it's sitting behind a double glass.

On the top it's and open circuit and on the bottom is connected with a 2 meters coaxial cable to the RTLSDR R820T receiver connected to a RPI.

Can you advice me about a better top and bottom termination and if an inline amplifier directly placed on the botton of it can boost noticeably the detection performance?
Thanks
 

ab cd

Senior Member
I've build my ADSB collinear antenna with 6 coaxial elements and it's doing a great job, over 100nm of coverage and it's sitting behind a double glass.

On the top it's and open circuit and on the bottom is connected with a 2 meters coaxial cable to the RTLSDR R820T receiver connected to a RPI.

Can you advice me about a better top and bottom termination and if an inline amplifier directly placed on the botton of it can boost noticeably the detection performance?
Thanks
(1) What is the height at which your antenna is located? 100nm is great with 6-element coco, if your antenna is indoors & at ground floor. It is not great , if it is at a height above roof line of your & surrounding houses/buildings/trees.
(2) Double glass will not make much difference if it is not reflective type.

For comparison:
(1) My Setup 1:
Antenna: 4-element, open top, coaxial collinear made of RG6 Coax.
Mounting height: inside an apartment 60 feet above ground, near large double-glass windows around.
Coax cable between antenna & Receiver (DVB-T USB) = 15 feet / 5 meters RG6 commercial Coax.
Max Range 200-250 nm

(2) My Setup 2:
Antenna: 4-element, open top, coaxiall collinear made of RG6 Coax.
Mounting height: inside an apartment 60 feet above ground, near large double-glass windows around.
Coax cable between antenna & Receiver (DVB-T USB) = 50 feet / 16 meters RG6 commercial Coax.
Amplifier (13-18 dB) at 15 ft from antenna
Max Range 200-250 nm
 
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giacomo1989

Member
(1) What is the height at which your antenna is located? 100nm is great with 6-element coco, if your antenna is indoors & at ground floor. It is not great , if it is at a height above roof line of your & surrounding houses/buildings/trees.

(2) Double glass will not make much difference if it is not reflective type.
2)
Thanks. It's the normal one. Just for thermic insulation.
1)
It's located inside my house in front off the window. 10 meters from the ground

The fact is that I live in a valley and there are mountains all arround so I don't even know much to expect in terms of coverage.
I've to do some calculation about my sight (in terms of angle)

For your info i checked my collinear and it hasn't got any shortcircuits.
 

ab cd

Senior Member
....The fact is that I live in a valley and there are mountains all arround so I don't even know much to expect in terms of coverage.
I've to do some calculation about my sight (in terms of angle).......
You can check your max range from the site http://www.heywhatsthat.com using following data:
(1) your latitude & longitude
(2) your antenna height above ground

Please see my post # 307 on page 16 for detailed steps & screenshot.

.
 

giacomo1989

Member
You can check your max range from the site http://www.heywhatsthat.com using following data:
(1) your latitude & longitude
(2) your antenna height above ground

Please see my post # 307 on page 16 for detailed steps & screenshot.

.

It's showing exactly the same area I can actually see airplanes right now!!! Amazing!!!! I think I cant reach any further!

If I trace the line to the most distant point.. I get 120 miles.. 104nm which is my case...

Damn mountains :)
 
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ab cd

Senior Member
It's showing exactly the same area I can actually see airplanes right now!!! Amazing!!!! I think I cant reach any further!

If I trace the line to the most distant point.. I get 120 miles.. 104nm which is my case...

Damn mountains :)
Yes you can reach further, if you tie your antenna to a big helium filled baloon floating at 1000 feet+ above ground, or still better at least at the same height as the mountain peaks. :D ;)
 
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ab cd

Senior Member
Well, my last post was a joke: It is a solution, but practically nearly impossible to implement.

Increasing the height of antenna theoretically does improve the range, but not much. On the "heywhatsthat" site, plot your maximum range for different antenna heights like 20m, 30m etc to see the increase in max range with increasing antenna heigt.
 

giacomo1989

Member
Well, my last post was a joke: It is a solution, but practically nearly impossible to implement.

Increasing the height of antenna theoretically does improve the range, but not much. On the "heywhatsthat" site, plot your maximum range for different antenna heights like 20m, 30m etc to see the increase in max range with increasing antenna heigt.

Not so much change :) Thanks
 

ab cd

Senior Member
Not so much change :) Thanks
That is what the theory says, unless you increase antena height by hunreds of feet.

Just out of curiocity, try "heywhatsthat.com" for your location with antenna heights 1000, 2000, & 5000 feet.
 
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jepolch

Active Member
I have gobbled up this thread over the last few days and learned so much! ab cd, this morning I built your 4-element coco (post #358 above). I made it out of RG59U because it was my first test and I have a lot of that cable. I installed it outside my window about six feet above the ground and practically doubled my coverage. I am using a Raspberry Pi and USB receiver dongle. I had been using the little whip antenna that came with the dongle til now. Next I'm going to build an 8-element coco out of RG6 and put it higher. Much fun!

Have you ever done an analysis of the antenna from QST Magazine January 2013? It's similar to your coco, but they leave a 1/8" gap between the segments.
http://www.arrl.org/files/file/QST/This Month in QST/January 2014/VirtualRadarJan2013QST.pdf
 

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ab cd

Senior Member
@jepolch:

Congratulations on your first successful CoCo.

(1) RG59U has PE (polyethylene) insulation which has Velocity Factor of 0.66. This gives element length = 0.66 x 275/2 = 91 mm.

What is element length in your CoCo?

(2) Smaller gaps between elements gives better performance.

With push-pin construction, it is possible to reduce this gap to the thickness of tape or paper inserted between elements, and is fraction of a mm.

With soldered construction, larger gaps are required to avoid shorts.
 

jepolch

Active Member
@jepolch:

Congratulations on your first successful CoCo.

(1) RG59U has PE (polyethylene) insulation which has Velocity Factor of 0.66. This gives element length = 0.66 x 275/2 = 91 mm.

What is element length in your CoCo?

(2) Smaller gaps between elements gives better performance.

With push-pin construction, it is possible to reduce this gap to the thickness of tape or paper inserted between elements, and is fraction of a mm.

With soldered construction, larger gaps are required to avoid shorts.

Thanks! The element sections are 114mm. It was based on your RG6 design. Can I correct it by changing the space in the gap to the feeder line? I can always make a new antenna. It was pretty quick.
 

ab cd

Senior Member
Thanks! The element sections are 114mm. It was based on your RG6 design. Can I correct it by changing the space in the gap to the feeder line? I can always make a new antenna. It was pretty quick.
The difference in length is too big (114 - 91 = 23 mm) to be compensated by adjusting the gap. Better make a new one with right length of elements.
 

jepolch

Active Member
The difference in length is too big (114 - 91 = 23 mm) to be compensated by adjusting the gap. Better make a new one with right length of elements.

You think I should go with RG6 next time? The center elements would definitely be stronger and easier to push in!
 

jepolch

Active Member
The difference in length is too big (114 - 91 = 23 mm) to be compensated by adjusting the gap. Better make a new one with right length of elements.

Oh, and one more thing, would that compensation be reducing the gap by 23mm or increasing?
 

ab cd

Senior Member
Oh, and one more thing, would that compensation be reducing the gap by 23mm or increasing?
I have to calculate using antenna simulation softwarere on my Desktop. I am away from home (replying from phone). Will do simulstion this weekend when at home. Meanwhile you can go ahead without compensation i.e. normal coco. Later you can add the compensation by changing the bottom piece only and modifying the feeder cable end to add compensation.
 
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