best antenna

[loplo]

Amplifier, injector and stuff arrived. I'm running some test now, number of hits has been increased.
The only issue I notice is that low flying planes are not followed anymore. I live below the glide path of the main runway at CGN, but no airplanes are tracked. Before I was able to track planes all the way down to ~450ft.

[abcd567]

......
Found this one, which clearly is an easy to do DIY project....
[ATTACH=CONFIG]5049[/ATTACH]
... but how he does his active element and the cable connections are not clear.

........

I have enhanced your drawing (see below). Is it helpful to solve your problem of connection of active (Driven) Element to Coax?
ADS-B_8EL-Rev1.JPG

[HermanZA]

It does help - thanks for your trouble in doing that.

Driven/Active Element: so the coax feedline gets split, the centre wire goes to the top half of the element (65.5mm) and the braid to the bottom half of the driven element (also 65.5mm). As per previous builds and experiments you did (I recall PeterHR started with something similar): this forms a very simple dipole antenna - top active, bottom passive. Element lenght of 131mm as per these specs. Would the gap between these two parts play any significant role? Small as practically possible to keep to the required element lenght?

Directors: As per this specific image, it seems the body of the antenna is made of some form of coax cable or maybe thin PVC tubing (the printing on it makes me to believe it could be either or), where the directors are pushed through the stiffening member (cable/PVC tube). It seems the rest of the antenna (body and directors) are not electrically linked in any way to the driven element? The directors mainly used to determine the directionality (and perhaps phasing?) of the antenna.

So with some PVC tubing, thin copper rods, some hot glue (or similar), some soldering skills, one should be able to construct a basic ADSB Yagi, as per these specs:



Now when I go to http://www.k7mem.com/Electronic_Note...html#Boom_Info it seems that this design has an all-metallic body (the default option), where the whole body (the boom + directors) forms 1 conductive unit. But adding the active element there is way more complicated as it needs to be insulated from the boom/body, thus we can say this is a more complex and challenging build, with more little gremlins that could slip into the build.

Am I correct with my above assumptions (I know what they say about assumptions!) and the way I interpret the information?

[abcd567]

Yagi-Uda Antenna

Yagi_Uda.PNG . Yagi-Uda on Tower.jpg . Yagi-Uda 2.jpg

The Yagi-Uda antenna consists of a number of parallel thin rod dipole elements in a line, usually half-wave dipoles, typically supported on a perpendicular crossbar or "boom" along their centers.

There is a single driven element driven in the center, consisting of two rods, each connected to one side of the transmission line.

There are a variable number of parasitic elements (reflectors & directors). The reflectors are on one side & directors on the other side of driven element.

The parasitic elements (reflector & directors) are not electrically connected to the transmitter or receiver, and serve as resonators, re-radiating the radio waves to modify the radiation pattern.

Typical spacings between elements vary from about 1/10 to 1/4 of a wavelength, depending on the specific design.

The lengths of the directors are slightly shorter than that of the driven element, while the reflector(s) are slightly longer.
.
The radiation pattern is unidirectional along the axis perpendicular to the elements in the plane of the elements, with the main lobe off the end with the directors.

Parasitic elements (reflector & directors) have a point of zero RF voltage at their center, so they can be attached to a conductive metal support at that point without need of insulation, without disturbing their electrical operation. They are usually bolted or welded to the antenna's central support boom.

The driven element is fed at center so its two halves must be insulated where the boom supports them.

Only one reflector is generally used since the improvement of gain with additional reflectors is negligible.

However increasing number of directors improves gain & directivity. Yagis have been built with up to 30-40 directors.

[Rooster]

Ive had great success with a bi-quad antenna for WIFI (2.4gHz)

Easy to make, but you MUST measure accurately.... even easier with 1.09gHz ! (as dimensions will be larger)
I used some solid PTFE cable with pre-attached plugs as the centre feedpoint and support for the "bowtie" mounted over a bit of copperclad PCB board.

Pic show similar antenna...
3060000000054059.JPG

[kucengemok]

any plan/diagram to make it?

[HermanZA]

I think I have gathered enough information now, will attempt to build one today. Have all the bits and pieces needed around the house. Will report back and take some photos of it. So hold thumbs, thats its going to be a "good" antenna that actually going to work! ;-)

[abcd567]

any plan/diagram to make it?

Bi-Quad Construction Details:

(1) http://trevormarshall.com/biquad.htm

(2) http://martybugs.net/wireless/biquad/

(3) http://www.engadget.com/2005/11/15/h...-dish-antenna/

(4) http://www.sorgonet.com/network/biquad/


Bi-Quad Dimension Calculator:

(1) http://buildyourownantenna.blogspot....alculator.html

(2) http://www.changpuak.ch/electronics/...a_designer.php

(3) Calculator App for Android Phones: https://play.google.com/store/apps/d...i.biquad&hl=en


Bi-Quad Analysis:
http://www.lecad.fs.uni-lj.si/~leon/other/wlan/biquad/

[HermanZA]

All I can say, this antenna is extremely fine measurements and tricky to construct, as you are working with very fine tolerances. Yeah, one extra element there, as I had a mm mistake on one.

IMG_20141115_140358_resize.jpg

Update: It aint pretty, but its done with specific attention to measurements and dimensions. Results to follow in a day or so. Unfortunately, planned maintenance on our electricity supply will leave me offline for the better part of Sunday.

IMG_20141115_180244_resize.jpg

[HermanZA]

Feedback on the Directional Yagi:

Building it was tricky and time consuming, specially trying to get the active elements mounted and connected to the feedline, as they need to be connected inside a 20mm PVC tube (in my case), so I used some twinflex wire to connect the end of the element to the feedline itself. That most probably will cause some minor degradation in the signal, but I could not see any way around it. Guess somebody will offer a better suggestion.

IMG_20141116_111928-edt_resize.jpg
Mounted about 5m above ground, feeding down with about 7m of RG6 coax straight into a dongle. No Amps. I know its not a perfect build, but I have identified some methods to make things easier and better for the next one. Oh yes, there will be a next one! Why ?

directional.JPG
Directionally this antenna gave a range of 360km and then it lost the AC. My CoCo lost this plane at 330km (Coco is 14m above ground, with inline amplifier). If I recall from when I switched over to the amplifier, one sees a range increase of around 80km. So in layman's terms: this Yagi is sees about 80km further (30km real difference + >50km amplifer difference). I wonder what the range increase will be, was it mounted right under the Coco!

You can see its is very directional, but not totally blind close behind and to the sides. Perhaps our Resident Antenna tester, ABCD, should give this one a go when he has some time and give his opinion on range. Since he is located high up in a building and all his testing is conducted from the same place and height....

So forumates, any comments or ideas ?

[trigger]

Hi Herman,
Good job !! Build another 3 and have them mounted at right angles . I've no idea how you would bring the 4 signals together I'm sure abcd will have some input.

[loplo]

Amplifier, injector and stuff arrived. I'm running some test now, number of hits has been increased.
The only issue I notice is that low flying planes are not followed anymore. I live below the glide path of the main runway at CGN, but no airplanes are tracked. Before I was able to track planes all the way down to ~450ft.

Solved playing with gain. Still testing, but for the moment 42 gives me nice results.

[abcd567]

Hi Herman,
Good job !! Build another 3 and have them mounted at right angles . I've no idea how you would bring the 4 signals together I'm sure abcd will have some input.

Coupling multiple antennas to one feeder is a tricky job.

The antennas have to be placed precisely relative to each other, connected to each other & feed coax by a phasing harness, which again is made up of precise lengths of coax.

[abcd567]

Feedback on the Directional Yagi:
.............Mounted about 5m above ground, feeding down with about 7m of RG6 coax.......
.........Directionally this antenna gave a range of 360km and then it lost the AC. My CoCo lost this plane at 330km (Coco is 14m above ground, with inline amplifier)...........

Congratulations for making a successful Yagi, the first of this forum/thread. Waiting for results of your next one.

.........Perhaps our Resident Antenna tester, ABCD, should give this one a go when he has some time and give his opinion on range. Since he is located high up in a building and all his testing is conducted from the same place and height.......

Oh no!
The repeated testing-tweaking-simulating-calculating-remaking of the wild CoCo, without reaching any concrete solution for an easily reproduceable, reliable performance CoCo, has made me fedup with antenna testing. For now I have taken a break. Will do Yagi after a while.

[Rooster]

Hi Herman,
Good job !! Build another 3 and have them mounted at right angles . I've no idea how you would bring the 4 signals together I'm sure abcd will have some input.

Nice theory, but the losses in the combiner or phasing harness would negate the benefits of using beams in the first place !