ADS-B DIY Antenna

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ab cd

Senior Member
Simulation 1 of 2: The Zigzag Franko-Spider
Poor Results :(

Franklin Spider Zigzag.PNG






Simulation 2 of 2: The Straight Franko-Spider
Good Results :)

Franklin Spider.PNG
 
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ab cd

Senior Member
Just curious how a 1/4 wave on top would do as opposed to the 138mm whip portion.. this I would think would "balance" out the initial 68 mm feed...

Jim
WELCOME ABOARD JIM!
Good idea, worth trying by simulation, as well as by making a prototype and putting it to trial run.
 

borchi

New Member
Hallo,

thank you... My wife is not happy with the solution... The antenna moves to outside :)

I got an inline amplyfier today with no result... Do i have to use a power injector?

My window is directed to the south-east, about 1 nm away from EDDB/SXF final aproach. Los is only blocked by one building.... Now the cool thing: I recive signals from the direction north, EDDT/TXL right trough my apartment :)

Have a nice evening....
 

ab cd

Senior Member
Hallo,

thank you... My wife is not happy with the solution... The antenna moves to outside :)
Typical "wifely" behaviour :(

Your wife's dislike to indoor antenna is a blessing in disguise. Now with antenna moved out, you will get better reception.

I got an inline amplyfier today with no result... Do i have to use a power injector?

My window is directed to the south-east, about 1 nm away from EDDB/SXF final aproach. Los is only blocked by one building.... Now the cool thing: I recive signals from the direction north, EDDT/TXL right trough my apartment :)

Have a nice evening....

Amplifier needs two more things to work:
(1) DC power supply
(2) Power inserter
See the diagram below (I have prepared this diagram for jepolch using his equipment, but it applies to other makes of equipment as well).



amplifier+power inserter+dc adaptor.png




http://m.ebay.de/itm/161662607940

power inserter 1.jpg



http://m.ebay.de/itm/331250951381

power inserter 2.jpg

 
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jepolch

Active Member
Good day everyone. I went up to the roof today and did a little tweaking. I cut all the legs and whips on my two spiders to 66 mm. They are made of 2 mm wire, and think that they would work better if shorter. So far, so good. It seems I'm getting at least as many aircraft and maybe a few more. At least I didn't make them worse! In the process of repositioning the radials I broke one off my "worse" spider. :( So now he has 7 legs. Doesn't seem to have hurt him much. I'm going to go up again soon and replace that with one of my conetennas, probably this one.

ETA: Almost forgot to mention, I also changed the angle of the radials to 35 degrees.
 

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ab cd

Senior Member
Good day everyone. I went up to the roof today and did a little tweaking. I cut all the legs and whips on my two spiders to 66 mm. They are made of 2 mm wire, and think that they would work better if shorter. So far, so good. It seems I'm getting at least as many aircraft and maybe a few more. At least I didn't make them worse! In the process of repositioning the radials I broke one off my "worse" spider. :( So now he has 7 legs. Doesn't seem to have hurt him much. I'm going to go up again soon and replace that with one of my conetennas, probably this one.
You are right.
Some text books do recommend reduction of length, obtained by free-air formula wavelength (in meters) = 300/Mhz, by a certain percentage, which depends on ratio of diameter of wire to wavelength.

According to correction factor graph attached below, for 2mm dia wire at 1090 Mhz, the reduction is 6% i.e. length should be 94%. For a quarter wavelength limb of 69mm, this works out to 69mm x 0.94 = 65mm.

Source of graph below: posted by member JLD in FR24 forum "best antenna":
http://forum.flightradar24.com/threads/3831-best-antenna?p=65115&viewfull=1#post65115

Edit: Image replaced by larger sized image provided by jeploch.

wire size ratio.jpg
 
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jepolch

Active Member
You are right.
Some text books do recommend reduction of length, obtained by free-air formula wavelength (in meters) = 300/Mhz, by a certain percentage, which depends on ratio of diameter of wire to wavelength.

According to correction factor graph attached below, for 2mm dia wire at 1090 Mhz, the reduction is 6% i.e. length should be 94%. For a quarter wavelength limb of 69mm, this works out to 69mm x 0.94 = 65mm.

Source of graph below: posted by member JLD in FR24 forum "best antenna":
http://forum.flightradar24.com/threads/3831-best-antenna?p=65115&viewfull=1#post65115

View attachment 1586
Geez, I wonder where I got the idea to shorten my legs? :rolleyes: I thought I'd try 66 mm first. It's easier to cut more off than add on.

ETA: @ab cd: Thanks for the info. That is good stuff.
 
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jepolch

Active Member
By the way, you may recall a few posts back I mentioned I was using a cable TV diplexer as a cheap (as in 2 for $5 cheap) high pass filter. My stats are up about 10% since I started using the diplexer.

ETA: I've tried connecting the diplexer in both directions (in/out aimed at antenna or receiver) and it doesn't seem to matter. I'm using the SAT and in/out ports.
 

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xforce30164

Active Member
Simulation 1 of 2: The Zigzag Franko-Spider
Poor Results :(

Simulation 2 of 2: The Straight Franko-Spider
Good Results :)

That is what I personally experienced aswell, reception of the single U-bend was a lot better than the S-bend.

ETA:

Hooked up the U-bend again,
frankenspider2.png


while the ebay antenna was receiving around 40 planes and 250 or so messages per second.

(Got a new RTL-SDR receiver/decoder as well, one of the noo-elec ones.)
IMG_20150410_114525.jpg

IMG_20150410_114552.jpg
 
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xforce30164

Active Member
Hallo,

thank you... My wife is not happy with the solution... The antenna moves to outside :)

I got an inline amplyfier today with no result... Do i have to use a power injector?

My window is directed to the south-east, about 1 nm away from EDDB/SXF final aproach. Los is only blocked by one building.... Now the cool thing: I recive signals from the direction north, EDDT/TXL right trough my apartment :)

Have a nice evening....

I have noticed the same behaviour, I get a better reception in the direction of the walls on the opposide side of my room when my antenna is placed near the window :p
 

xforce30164

Active Member
An easier way to get accuracy is to measure & mark on wire the points of bends while the whole wire is still straight, BEFORE starting any bending & cutting.

For example, for straight stub franko-spider, marking can be done on straight wire as follows:

STEP 1:
Point A - top of wire
Point B - 138mm from A
Point C - 66mm from B
Point D - 6mm from C
Point E - 66mm from D
Point F -69mm from E
Point G - 10mm from F (surplus)

STEP 2:
Make 90* bends at already marked points B, C, D, & E.

STEP 3:
Trim length at bottom according to SO239 to make finished height of lower-most section = 69mm.

Going to make another U-bend FrankenSpider right now to see how it compares to my other one (which has ~140mm of wire in the matching stub)

ETA: from where do you measure for the 69mm segment from the connector towards the first bend, from level/line A, B, or C?
IMG_20150410_121050.jpg

IMG_20150410_120833.jpg

IMG_20150410_120425.jpg
 
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