ADS-B DIY Antenna

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jepolch

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TACTICAL adsb ;) a bit of low level action from natures early spring Operation Red Flag
"GRIMREAPER1" and "SPADGER23"

Tcas alerts going off all over the place.. "traffic, climb, climb now whoop whoop" & " terrain, pull up, whoop whoop"

Some nice avoidance turns by spadger as he was intercepted by grim on the ILS approach downwind leg the to the 50ft birch tree strip in my back garden in the absence of his wingman.
A full "de-briefing" which was loud.. took place after his landing.
"Grimreaper1" continued on with his sortie circling the wider vicinity in search of additional bogeys to engage with.

..The Spidermag V2.1 gets them all !

:)
Nice antenna! I like it. I have a little whip that came with the dongle that I cut down to 69mm. I'll add some legs to it and give it a try.
 

xforce30164

Active Member
That's too bad. Sorry to hear it. The spider is a great antenna. I don't think we can do much better than that.
Don't be sorry man! It just proves again how darn good those spider are! I'm thinking if another design for the spider where instead of the single 1/4L radial, I'm going to make a triangle of three 1/4L sections. with the first segment being horizontal/@90* angle from the receiving 1/4L section. I'll also be moving/trying to move the ebay antenna up slightly higher to seehow much it improves in performance!
 

jepolch

Active Member
Don't be sorry man! It just proves again how darn good those spider are! I'm thinking if another design for the spider where instead of the single 1/4L radial, I'm going to make a triangle of three 1/4L sections. with the first segment being horizontal/@90* angle from the receiving 1/4L section. I'll also be moving/trying to move the ebay antenna up slightly higher to seehow much it improves in performance!
OK, I'm not sure how that would look. Can you give us a rough sketch? I get the perpendicular (90*) segment, but what's the rest of the triangle made up of?
 

xforce30164

Active Member
OK, I'm not sure how that would look. Can you give us a rough sketch? I get the perpendicular (90*) segment, but what's the rest of the triangle made up of?
its an equal-sided triangle, 60* corners, all sides 1/4L long. top view would be an X with in the center the receiving segment pointing towards you. each "leg" of the X would be the upper part of the triangle (pointig downwards, so the flat base is the horizontal part). the point would be resting on the ground.

Ill try and sketch/draw something tomorrow and hopefully be able to make a first prototype on tuesday.

ETA: Has anyone ever tried stacking spiders? (or maybe have them point at each other like >- -< (and then rotate 90* to have them vertical). could be another nice experimentational route to go down?
 
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jepolch

Active Member
its an equal-sided triangle, 60* corners, all sides 1/4L long. top view would be an X with in the center the receiving segment pointing towards you. each "leg" of the X would be the upper part of the triangle (pointig downwards, so the flat base is the horizontal part). the point would be resting on the ground.

Ill try and sketch/draw something tomorrow and hopefully be able to make a first prototype on tuesday.

ETA: Has anyone ever tried stacking spiders? (or maybe have them point at each other like >- -< (and then rotate 90* to have them vertical). could be another nice experimentational route to go down?
I haven't stacked any spiders, but it did occur to me to put a metal plate under the radials (but not touching) like a reflector. I think maybe @ab cd has done that.
 

xforce30164

Active Member
Achieved some better groundcover here at EHAM, with dual radial spider:
groundcover.png

IMG_20150406_101451_1428308692212.jpg


The increase in low-altitude reception gave me the the idea for the triangle-radials as explained before.
 
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Achieved some better groundcover here at EHAM, with dual radial spider:
View attachment 1555
View attachment 1556

The increase in low-altitude reception gave the the idea for the triangle-radials as explained before.


Hi Magforce,
I think you may be going with the idea of a variation on the discone antenna in your pic.
I had a lightbulb moment from your photo of the multi radial spider though.
Perhaps a 5/8 driven element against a 5/8 and 1/4 wave combo ground plane would work well.

A worry though would be that the discone is a popular design for its ability to pick up a multitude of bands (no one band particularly well i might add due to the fact that most factory ones are made for multiband ops) and it may suffer from GSM bleedover.

Due to your fine handy work on the bracelet antenna..stunning btw.
You certainly would get good ground cover from AMS if you made a cute little 1090 cubical quad with several reflectors. This would require careful measuring & construction. This one is very directional indeed .
Would beat any spider hands down for ground cover in your location I would wager.
 

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xforce30164

Active Member
Hi Magforce,
I think you may be going with the idea of a variation on the discone antenna in your pic.
I had a lightbulb moment from your photo of the multi radial spider though.
Perhaps a 5/8 driven element against a 5/8 and 1/4 wave combo ground plane would work well.

A worry though would be that the discone is a popular design for its ability to pick up a multitude of bands (no one band particularly well i might add due to the fact that most factory ones are made for multiband ops) and it may suffer from GSM bleedover.

Ah yea, you're right, It does look like a discone, but maybe because I'll be making the triangle-spider with all 1.4L segments for 1090Mhz that there is less bleed-over. Also, I'm looking into building a simple 1090mhz bandpass filter circuit to filter out all other stuff as much as possible and see if it improves reception. (IOW that the dB loss from the circuit does not have a bigger impact compared to the lower background noise of the final signal)

ETA:
With the driven element, I assume you mean the single 1/4L (in current spider design) of wire that points towards the sky?

ETA2:
Quick sketch of the triangle-spider antenna:
triangle-spider.png
 
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Hi xforce,
Yes the "driven element"is the centre whip, IOW the bit that does the business.
The ground plane are the legs which "focus" the signal to the whip.
Achieving perfect "focus" aka resonance is what its all about, but as ever there are caveats..
The more legs, the better the "focus" but the legs have to be exactly right, as the leg numbers increase, the accuracy of spacing and cutting and angular positioning (ground plane shaping) becomes more critical or the "focus" goes off some place in the vicinity of the whip but not onto the whip sweet spot. As the legs increase the whips sweet spot has a tendency to get smaller.
When you get it just right..you know about it and no mistake !

It is a labour of love though !...I have been messing about with antennas this since I was 8 yrs old and count on one hand the number of times I have got it just right,as good as it could ever be first time.
I have ruined lots of my homebrew antennas by over tweaking, and rescued a few by tweaking ..such is life !
The cantenna,plantenna and spider are all formed based on the idea of focusing that incoming signal and really honing it to the whip which, in the large part, remains unchanged in its specification for each design.



Theoretically the 5/8 wave driven element should give more gain than 1/4 wave, so a 5/8 spider should outperform a 1/4 wave one but the margin would I suspect be very small.
Another caveat here is that 5/8 would jump right in the pool of the GSM brigade with big signals packed tight into the band so the improved gain may be nullified by the additional unwanted signal pickup.

You triangle one has the DNA of a double discone going on there...but in a slightly different way.
Maybe this is what you had an idea of in the final line of post #2564 on this page.;)
 

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trigger

Member
A question about stacked dipoles.
I've gone back to airbus' design a few pages back using coax rather than twin lead. Whilst cutting the coax it occured to me that if I connect the top leg of the top dipole to the core of the coax, the top leg of the lower dipole will be connected to braid. That's because it is easy to cut the coax that way.
Should the top legs of each dipole be attached to core or doesn't it matter?
 
Hi trigg,
I would say no as you are working with 1/2 wave dipoles in a phased array, the harness would be connected out of phase.
The dipoles would not be 1/2 wave (ie the driven element of A1 working with its partner A2).
If you connected A1 directly to B2 via coax in the harness ,there would be a large impedance mismatch I think.
As said, "the art" of the stacked dipole array is almost black.
In simple terms, the degree of difficulty to hit the sweet spot would be akin to constructing a good 24 element coco x 100 fold.
The measurements and spacing are so critical.
Even ab cd , a very accomplished builder of notable standing, gave up and I can fully understand why he did so.
 
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xforce30164

Active Member
Hi xforce,
Yes the "driven element"is the centre whip, IOW the bit that does the business.
The ground plane are the legs which "focus" the signal to the whip.
Achieving perfect "focus" aka resonance is what its all about, but as ever there are caveats..
The more legs, the better the "focus" but the legs have to be exactly right, as the leg numbers increase, the accuracy of spacing and cutting and angular positioning (ground plane shaping) becomes more critical or the "focus" goes off some place in the vicinity of the whip but not onto the whip sweet spot. As the legs increase the whips sweet spot has a tendency to get smaller.
When you get it just right..you know about it and no mistake !

It is a labour of love though !...I have been messing about with antennas this since I was 8 yrs old and count on one hand the number of times I have got it just right,as good as it could ever be first time.
I have ruined lots of my homebrew antennas by over tweaking, and rescued a few by tweaking ..such is life !
The cantenna,plantenna and spider are all formed based on the idea of focusing that incoming signal and really honing it to the whip which, in the large part, remains unchanged in its specification for each design.



Theoretically the 5/8 wave driven element should give more gain than 1/4 wave, so a 5/8 spider should outperform a 1/4 wave one but the margin would I suspect be very small.
Another caveat here is that 5/8 would jump right in the pool of the GSM brigade with big signals packed tight into the band so the improved gain may be nullified by the additional unwanted signal pickup.

You triangle one has the DNA of a double discone going on there...but in a slightly different way.
Maybe this is what you had an idea of in the final line of post #2564 on this page.;)

I've indeed also been browsing through the double discones, but not sure yet. About the 5/8L with gsm interference, it would be a nice trial/experiment to have two spiders, one 1/4L withouth filter and the 5/8L with the biy ~1090mhz band-pass filter to see how much difference it makes. (and also try the 5/8 without the filter). that way you could maybe have the increased gain from the 5/8L and not as much interference from the GSM signals.

I've also been reading about the so-called shared-apex loop antenna, which is a relatively compact antenna for 0-30Mhz which is dynamically directional, IOW, you can "tune" it to a specific direction.

some more details are in this pdf and here's a short youtube vid. This might not be very relevant for 1090mhz but as I'm also working in the vhf/hf bands (or looking into what I can receive), it seems like a nice thing to try!
 

xforce30164

Active Member
Hi trigg,
I would say no as you are working with 1/2 wave dipoles in a phased array, the harness would be connected out of phase.
The dipoles would not be 1/2 wave (ie the driven element of A1 working with its partner A2).
If you connected A1 directly to B2 via coax in the harness ,there would be a large impedance mismatch I think.
As said, "the art" of the stacked dipole array is almost black.
In simple terms, the degree of difficulty to hit the sweet spot would be akin to constructing a good 24 element coco x 100 fold.
The measurements and spacing are so critical.
Even ab cd , a very accomplished builder of notable standing, gave up and I can fully understand why he did so.

I don't know exactly how, but this got me thinking, what if you would make an yagi-antenna where the reflector and director radials can be moved by stepper motors along the yagi-support beam and you have another (two) stepper(s) to move the whole antenna. In theory you could make a dynamic-band yagi, instead of the Log periodic design, which is very good wide bandwith, but maybe less gain for specific frequencies. (I also might try and make a LogPeriodic for its wide-bandishness)

ETA: Fractal Antenna's might be another cool experiment :D
pic from internet:
bv000012.jpg

(cool read: http://ag1le.blogspot.nl/2011/12/antenna-experiments-fractal-quad-for-28.html)
 
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I don't know exactly how, but this got me thinking, what if you would make an yagi-antenna where the reflector and director radials can be moved by stepper motors along the yagi-support beam and you have another (two) stepper(s) to move the whole antenna. In theory you could make a dynamic-band yagi, instead of the Log periodic design, which is very good wide bandwith, but maybe less gain for specific frequencies. (I also might try and make a LogPeriodic for its wide-bandishness)

ETA: Fractal Antenna's might be another cool experiment :D

Hi Xforce,
The bandwith of the 1090 adsb signal is quite wide, a simple log yagi may be okay with the directors at a fixed point . But again a caveat Marteen,
You could probably spend the rest of your days experimenting with reflector shaping and moving/adding/taking away & crossing directors on this variant !
The TV bods (antenna manufacturers) have been at it for years claiming one is better than another.

Pointing at AMS from your location to get the additional squitters would mean focusing (forming the illusion of that of a telescope with optics) also on what is in between your station and the airport. Unlike optical law though everything seen in the "antenna focus tube/line of sight and beyond" which is the theory of the yagi is in perfect focus so any other unwanted signals in the way will also be received "birdies" also.
 
1/4 wave 8 leg ground plane F connector Spider Experiment.

4 horizontal + 4 @ 45/60 deg. Centre element from some stripped down Webro WF100 coax core + dielectric.
A very apt backdrop in the photo too ! ;)

A bit too extravagant on materials here but what the heck, I pulled out all the stops here and threw caution to the wind.
I used one of my brand new F connectors.:)

From all the stuff on this thread, I bet some savvy people could flip a nice profit on fleabay or suchlike.
 

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xforce30164

Active Member
1/4 wave 8 leg ground plane F connector spider experiment.
4 horizontal + 4 @ 45/60 deg.
A very apt backdrop in the photo too ! :)
My first reaction was like, "Wait, whut, what is that candle doing in the middle as active element?" :p but then I read the text. looks awesome, cool idea, love to see the results, will be nice to compare with my triangle-radials spider when I build it =D
 
My first reaction was like, "Wait, whut, what is that candle doing in the middle as active element?" :p but then I read the text. looks awesome, cool idea, love to see the results, will be nice to compare with my triangle-radials spider when I build it =D
Cheers xforce, post edited so as not to cause candle confusion !
 
Also, just stumbled across this chip/IC/SAW filter, its perfect for 1090Mhz!
Hi xforce,
In short..It looks like an SMD, In the few meetings we have had in the last 15 yrs or so,I cannot say we (Myself and SMDs) "get along".:mad: I am not equiped with boinic sight..Over and out !

Edit, Im not good with the newer stuff.
I still marvel at why it takes me 5 times longer to type a message on here than send the exact same message in cw in my straight nato key..technology eh ? hmmmo_O
 
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