ADS-B DIY Antenna

Status
Not open for further replies.

ab cd

Senior Member
EXAMPLES OF FAILURE OF SIMULATION SOFTWARE
Most of Collinears posted on internet are flawed design. These collinears are shown to be high gain by posting the supporting results of simulation. Almost no one posts results of actual measurements of Gain & SWR, or results of comparison with a standard benchmark antenna of known parameters.

It is my experience that these simulation software give results with errors which may be of the order of 5% to 10%, which is too high for accurate optimization of collinears. To highlight this, I optimized wire collinears by simulation, and calculated parameters of these collinears and a 1/4 wavelength (non-collinear) benchmark antenna. I then made prototypes and put on trial run with reference to benchmark antenna.

Results after optimization by simulation software were:
Benchmark antenna - Standard Cantenna: Gain = 1.48 dBi, SWR = 1.28
Antenna Under Test 1 - Coiled Cantenna: Gain = 2.99 dBi, SWR = 1.17
Antenna Under Test 2 - Franklin Cantenna: Gain = 3.13 dBi, SWR = 1.9

The simulation results show that both the Antennas Under Test should give better performance than Benchmark antenna. However when I made the prototypes using optimized dimensions given by simulation, and put on trial, results were opposite. This proved the unreliability of simulation results. I will now try to find the optimum dimension by trimming the prototypes.

I have actually made 2 whips under test only, and simply pulled out the 1/4 wavelength (69mm) whip of existing Standard Cantenna and inserted in its place the Whip under test. This made all other factors identical for the benchmark & under test antennas.

Prototypes (top to bottom):
Standard Cantenna, Coiled Cantenna, Franklin Cantenna


Standard Cantenna 480x640.jpg


Coiled Cantenna 480x640.jpg


Franklin Cantenna 480x640.jpg



Simultion (top to bottom):
Standard Cantenna, Coiled Cantenna, Franklin Cantenna


Simulation Standard Cantenna 800x720.jpg



Simulation Coiled Cantenna 800x720.jpg



Simulation Franklin Cantenna 800x720.jpg




 

ab cd

Senior Member
The 4nec2 & mmana-gal softwares give large error for complicated antennas involving curved radiating wires/surfaces like coils of the collinear whip & shield of coco. Therefore for these antennas, the impedance value given by simulation have substantial error. Hence basing impedance matching capacitor & TL value on these values again gives poor results, and large number of trial & error attempts are required, which is tedious.

The Franklin whip consists of only straight sections of wire, hence error is not large. In my opinion, the reason of poor performance of Franklin Cantenna is not wrong optimized dimensions. Rather it is due to SWR which is nearly 2, while 1/4 wave whip has SWR 1.3, and this difference in SWR results in Franklin Cantenna performing inferior to Standard 1/4 wave Cantenna.

Anyway I will make & try the "Transmission Line + Capacitor" impedance match shortly and come back with the results, may be success, may be failure.

Impedance Matching of Franklin Cantenna 462x1024.jpg



 
Last edited:

ab cd

Senior Member
Impedance matching calculated by Smith Chart, then followed by trial run and trimming

I have installed Impedance matching for Franklin Cantenna by "coax+capacitor" as shown in diagram in my last post above. I tried 3 lengths of coax: 85 mm, 80 mm, and 75 mm.

The left-most part of graph is for the period when Cantenna had 1/4 wavelength (69 mm) whip. I then replced 1/4 whip by Franklin whip, and you can see drasticdrop in performance. I then inserted Impedance matching 75 mm coax +2.7 pF capacitor, then after about 15 minutes, changed piece of coax by 80 mm coax, then again after 15 minutes, changed piece of coax to 85 mm coax. As you can see best results are are 80 mm coax piece, as calculated by Smith Chart, very promising.

I did not have 3 pF capacitor, so I have used 2.7 pF capacitor available with me. May be using aslightly higher or lower value of capcitor will gurther improve the performance. Someday,Iwill visit our local electronics & hobby shop and purchase many different values of capacitor in 0.5 pF to 10 pF range, and prrform trial and error again, this time keeping piece of coax fixed to 80mm, and changing the capacitor value between 1pF and 4 pf insteps of 0.5 pF.

Below is rrd collectd graph which shows the results.

Franklin Cantenna Impedance Matching Result 597x290.png


DSC03981-R.JPG


.
 
hello again folks,

since autumn came, I had quite more times to experiments, so I built some "proof of concept" antennas: biQuad, J pole and slim Jim and recently, a couple of super J poles antennas. I was very excited at the beginning , but now, I am a bit confused. So, let's say - it's very hard to do a great antenna but it's really hard thing to tune it and test it... Please see my precious, but the point is not obvious.Anyway, let's go to the point:
I made my few days long tests of each of those antennas and then I shared all testing equipment (including a few feet of coaxial cable, an amp, an amp power supply ~18DCV, a dongle, and a set of testing antennas) to my friend, who lives ~10 miles away of me. I didn’t tell him, which of those antennas is my favourite one, and after about of week of testing, we meet again and share our experiences. And as of my and his winner was J pole antenna! I was surprised, but I do believe that it can be a result of the precision... anyway, the winner is J pole so far.
But... a few days ago I was testing a couple of super J pole antennas. Results seems promising, because of nice range, but then... so, well, today I got a few pieces of superb quality of RFF 1/2'' 50 coaxial cable (some guys were disassembling something around the roof on the building where I'm working on (probably kind of old cellular equipmet), and they gave me some short pieces of this cable when I asked them for... ) and it could be a good base for COCO antenna...
So, guys, what do you think about coco :D ? but the real question is, how to do it well... ?

best regards!
Piotr
 

Attachments

Last edited:

ab cd

Senior Member
... today I got a few pieces of superb quality of RFF 1/2'' 50 coaxial cable...........So, guys, what do you think about coco :D ? but the real question is, how to do it well... ?
(1) Find the manufacturer & model number of REF 1/2" 50 coax.
(2) Search web for the manufacturer's data sheet for this cable.
(3) From data sheet, find out Velocity Factor for this cable.
(4) Calculate element length = Velocity Factor x 275/2 mm
(5) See example here. The Velocity factor may be different for example cable (LDF1-50) & your cable (REF 1/2" 50), hence your element length will be different from example coco's element length.

http://ads-b.ca/LDF1-50/coco/
http://ads-b.ca/LDF1-50/super-antenna/
http://ads-b.ca/antenna-collinear-F-CYYZ2/


http://forum.flightradar24.com/threads/3831-best-antenna?p=53124&highlight=super+antenna#post53124


Peter Fairli LDF CoCo_img_9712_std.jpg
 
(1) Find the manufacturer & model number of REF 1/2" 50 coax.
(2) Search web for the manufacturer's data sheet for this cable.
(3) From data sheet, find out Velocity Factor for this cable.
(4) Calculate element length = Velocity Factor x 275/2 mm
(5) See example here. The Velocity factor may be different for example cable (LDF1-50) & your cable (REF 1/2" 50), hence your element length will be different from example coco's element length.

http://ads-b.ca/LDF1-50/coco/
http://ads-b.ca/LDF1-50/super-antenna/
http://ads-b.ca/antenna-collinear-F-CYYZ2/


http://forum.flightradar24.com/threads/3831-best-antenna?p=53124&highlight=super+antenna#post53124


View attachment 2406
Hi ab cd,
thank you for the response! I already did what you just suggests (so I found data sheet to the cable I have, vf is 0.82, I found such sites and those examples too. I was very care cutting an elements from this hard cable (can't feel my fingers today ;) ), so I do believe that dimensions are accurate as far as I could get them). And I made my COCO for try-run (not jet soldered but lets say, sticked the pieces by thin wire and insulated tape), and since yesterday's evening, I am testing it a bit from my kitchen's window. And so my first conclusion are:
I did such version as on the attached screen (F-CYYZ2, which in fact was my pattern;), but I found that the shorted rod on top giving much worse result when opened, so I opened it today and the performance increase immediately.
I also found, that the feed line impact to the range, what shouldn't be, so I was trying to do a balloon sleeve, but all try with balloon failed - range was dramatically doped and the overall count of planes too.

As for now, COCO had 8 elements, including this one on top (which is 1/4 wavelength shield and 1/4 wavelength naked rod from the centre of cable). The maximum range is up to 350km, and is equal to my current franklin antenna located outside ~2 meters higher. But the count of planes, comparing both antennas is obviously worse on COCO due to "shadow" of the buildings around.

And so, here my questions are: how to prepare proper balloon sleeve for coco? I found two methods - one is lets say a "can opened upside" and second one is a "can opened downside"... ?
And, what kind of top should I do: shortened or opened and shall it be 2x1/4 wave, 1x1/2 wave made from shield, or 1/2 wave made from center rod... ? Any advices will be appreciated :)
Best regards,
piotr
 

Attachments

ab cd

Senior Member
@pgjp6910

Hi Piotr
Cutting the Coax:
Peter Fairlie cut the coax using a pipe cutter, which made it easier to cut the heavy cable shield.
Peter also cut the coax at the grooved part of the corrugated shield, making it easier to cut, and each piece having exact same number of rings of corrugated shield.


Top & Bottom of Coco:
Well I have not been able to fully understand the "top" & "bottom" of a Coco :)


top
(1) shorted or open??????
(2) whip or no whip???????

bottom
(1) sleeve open end facing upwards (towards antenna) or downwards (towards receiver)?????
(2) how much length of coax between last element of coax & the sleeve?????

Please see this post (also read earlier & later posts):
Help with coaxial collinear antenna: http://www.eham.net/ehamforum/smf/index.php/topic,38371.msg870331.html#msg870331


See this page (click on several "See fig ...." links on this page to see sketches).
Omni-Gain Vertical Collinear: http://www.repeater-builder.com/antenna/wa6svt.html

 
Last edited:
@pgjp6910

Cutting the Coax:
Peter Fairlie cut the coax using a pipe cutter, which made it easier to cut the heavy cable shield.
Peter also cut the coax at the grooved part of the corrugated shield, making it easier to cut, and each piece having exact same number of rings of corrugated shield.


Top & Bottom of Coco:
Well I have not been able to fully understand the "top" & "bottom" of a Coco :)


top
(1) shorted or open??????
(2) whip or no whip???????

bottom
(1) sleeve open end facing upwards (towards antenna) or downwards (towards receiver)?????
(2) how much length of coax between last element of coax & the sleeve?????

Please see this post (also read earlier & later posts):
Help with coaxial collinear antenna: http://www.eham.net/ehamforum/smf/index.php/topic,38371.msg870331.html#msg870331


See this page (click on several "See fig ...." links on this page to see sketches).
Omni-Gain Vertical Collinear: http://www.repeater-builder.com/antenna/wa6svt.html
Hi ab cd,

many thanks for above links, seems that it's what I was looking for!
As of my coco: my current built is only the proof of concept but I was trying to be precise and gather as much experience as I can (I have some more cable so I hope it will allows me to build another one coco :) ). So, have to cut the wire using sharp knife (I don't know how is the proper English name of that kind of knife, but it's really sharp and thin, so, I can cut soft cooper wire with a little effort ;) , but the problem was that the cooper shield is coiled while Peter's wire wasn't, so I'm not sure if pipe cutter will be good for this).
Yesterday night I made some development of my coco and for now it has 8 half wave elements and one a quarter + quarter element on top. I described it on the paper and attached it's draft here. Also I made a simple schema of my meaning of shorted and opened top. And my meaning of sleeve. Sorry for not being precise, but English is not my first language, so it's a bit hard for me to describe what I mean.

When I will be more advanced on development and testing, I will post a picture of my build and will compare my two antennas: franklin (outdoor) and coco indoor. It seems interesting so far:).

Edit:
Updated diagrams.

Best regards,
piotr
 

Attachments

Last edited:
Hi ab cd,
once again - thank you for link. I've seen it before and it inspired me to ask for the best solution in case of top of the coco. But anyway, I think I will stay with my current solution. Seems to be good enough to keep it as it is for now (which is in fact the same as Peter's Fairlie solution).
In case of sleeve balun, I've seen three different kinds of it, so I wasn't sure which one is correct, but I think I can check it in practice. As for now, I have not any yet...

Yesterday I connected my developed CoCo to my second RPi set and gather statistics to see how does it works in the long term in comparison to my main set. I hope I will find some new room to improvements (also based on links from your posts) and after that, I will soldered all pieces together and settle this set in the quite new location :)


Best regards,
piotr
 
IMGA0377.JPG


Well, can't blame the crows for this. We've had back to back gales here for the past month or so and the set-up handled them pretty well, only moving slightly askew a couple of times. Since I got the plastic pipe tight enough not to move, fatigue has taken over and the conduit elbow joint has finally had enough.
Mount mk.2 will be from 1.25" push fit waste which fits snugly into the 1.5" ally tube. A t-pc and 2 elbows, correctly spaced, should give me a "U" shape > a wavelength apart to run 2 antenna like before.
 
A question for the antenna gurus in here.

I made a test with my cantenna two days ago, I removed the 68 mm top and replaced it with a 1 metre copper wire and the message rate went up a lot but the range was a little less, how come? Is it because it is more material in the longer wire I get more messages, but why worse range?
 
Thank you, thats probably correct. It wasnt as good as I first thought, when I put back the original whip my plane count tripled but also the message rate dropped. To use one of each at the same time maybe would work, tests will continue.
 
Last edited:

ab cd

Senior Member
A question for the antenna gurus in here.
I made a test with my cantenna two days ago, I removed the 68 mm top and replaced it with a 1 metre copper wire and the message rate went up a lot but the range was a little less, how come? Is it because it is more material in the longer wire I get more messages, but why worse range?
Likely you radiation pattern changed with the addition and you lost distant coverage but picked up more local lower altitude traffic.
Wavelength at 1090 MHz = 275 mm
Your wire = 1 m = 1000 mm = 1000/275 wavelengths = 3.6 wavelengths
See below animated radiation pattern showing how the radiation patern changes with length of wire.
The ideal pattern for ADS-B is Lazy 8 (8 is lazy and lying in bed, like this
lazy 8.png
)



.
 
Thank you very much for the simulation, ab cd! This is really interesting if I understand it correct. We use 1/4 wavelength whips but in your simulation it show a bigger 8 with 1 full wavelength and even better range with 4 x wavelength but not the best pattern. Now I must try full wavelength and 4 x wavelength to see how the range will be.
 

ab cd

Senior Member
Thank you very much for the simulation, ab cd! This is really interesting if I understand it correct. We use 1/4 wavelength whips but in your simulation it show a bigger 8 with 1 full wavelength and even better range with 4 x wavelength but not the best pattern. Now I must try full wavelength and 4 x wavelength to see how the range will be.
The animation I posted is for a DIPOLE, i.e. double whip, one up one down. The groundplane antennas (Spider, Cantenna etc) are MONOPOLE i.e. single whiped, one whip replaced by the groundplane. A 1/4 wavelength monopole+groundplane is equivalent to 1/2 wavelength dipole (2 whips each 1/4 wavelength). The 1 wavelength dipole is same as 1/2 wavelength monopole+groundplane, and has a bigger 8 i.e. higher gain in dB.

The reason 1 wavelength dipole (= 1/2 wavelength monopole + groundplane) is not popular is that its impedance is several hundred ohms, and does not match with the 75 or 50 ohms coax & recievers. Due to the impedance mismatch, only a fraction of the signal picked by antenna is transferred to the receiver. To enable maximum signal transfer, impedance matching arrangements are to be inserted between antenna & receiver. This makes full wave (1 wavelength) dipole or 1/2 wavelength monopole unpopular.

The 1/2 wavelength dipole (= 1/4 wavelenght single whip + groundplane) has an impedance of 75 ohms, which perfectly matches with 75 ohm impedance of coax & receiver, resulting in maximum transfer of signal from antenna to receiver. The 1/4 wavelength whip + groundplane is therefore most popular antenna as it does not require any impedance matching arrangement.

The Dipoles longer than 1 wavelength (Monopoles longer than 1/2 wavelength) have disadvantage of both higher impedance and undeireable radiation pattern.
 
Thank you very much for a very informative answer! I guess I can stop my tests with different whips then as I reach 220 NM indoor in a window with my cantenna. My goal is 260 NM as I have a very interesting airway there with lots of traffic, but can´t reach it...

Is the window always the best place for an indoor antenna or will it be better higher up even if it isn´t placed in a window?
 
Status
Not open for further replies.
Top