ADS-B DIY Antenna

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Richard Lee

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It seems you have now reached the fabled 9th Ring of Albany!
Looks like some range improvement to me.

When you drop an eastbound plane at Albany, maybe I'll pick it up! :)

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Richard Lee

Member
The in-line amps that I've seen used for satellite systems are designed to get their power from the indoor receiver unit.
Most will run on 12 to 15 vdc. Their current requirements are normally quite low. 200 ma would likely be about the max needed..

Go back to page 1 of this thread to see how ab cd supplied power to his LNA.. Here's the picture. He merges VHF with 1090.
You might not want to add those parts.


Warning:
Look at the bottom line of text on that amp. "Power Pass DC"
I had one of these inline amps years ago, and I think the DC input on mine, was fed right on up to the antenna.
Because the same power was used by the Down-converter at the dish.. So, the unit was a DC pass-thru.
You should be careful if you have that type of amp.. Since it would feed DC-power up to your antenna's driven elements.
If they short to ground, that would load up the power supply and maybe over-heat it or melt some of it's parts..

 

PaulGulliver

New Member
Thanks for the reply Richard, I wasn't sure if they would work down to 12v - I'm not sure how well stabilised these cheap power supplies are so a 12v unit with a low load may well be nearer 14v in any case.
Thanks for the warning about the dc feed through, I hadn't noticed that - could easily result in a fried psu
 

Richard Lee

Member
I have a box full of old 12V wallwarts (warm transformer type) that measure 13 to 16 volts with no load.
Since the amp is likely a very light load, you shouldn't expect very much drop when it's running.
So, don't buy a 15v wallwart w/transformer inside, since it might run the amp at 20vdc!

If you build the power-inserter (shown above), you might want to add some capacitors to the DC power input point.
Connect the negative side to ground, of a 4.7 to 10 mfd and put a disc 0.002 (or similar) across the larger cap.
That might filter out any 50-60hz hum from the AC line.
It might not be needed, if the regulator device inside the amp is well designed.

Cheers,
Rich
 

sergiomaria

New Member
IMPROVED RANGE BY CHANGING STUB CONDUCTOR SPACING
For my Franklin antenna, I was using an impedance matching stub in which spacing between stub conductors was 5mm (due to 5mm spacing of terminal screws in the terminal block for adjusting the tap position).
I dig-up some theory about impedance matching by stub, and found that if I increase the spacing of stub wires to 10mm, I will get a much better impedance match.
I increased the spacing to 10mm and put antenna on trial run for 24 hrs. I could gain about 75 to 100 km extra in all directions.
Below are two coverage screen-shots, one for a 5mm spacing stub, and other for 10mm spacing stub.


Image 1 of 3 - Coverage with 5mm spacing of Stub Conductors
View attachment 352


Image 2 of 3 - Coverage with 10mm spacing of Stub Conductors
View attachment 353


THEORY & CALCULATIONS

Image 3 of 3 - Calculations
View attachment 354
For matching impedance of Antenna with impedance of Feed Cable, the quarter-wavelength stub's impedance ZSTB shoul be:
ZSTB = √ (ZFDR x ZANT)
For RG-6 cable: ZFDR = 75 Ohms
For Full-Wavelength Dipole / Franklin Antenna: ZANT = 1600 Ohms
Hence required stub impedance ZSTB = √ (75 x 1600) = 346 Ohms

Calculated Stub impedance from it’s dimensions
ZSTB = 276 log10 (2S/d)
where S = conductor spacing in mm, d = conductor diameter in mm
Stub conductor is #18 AWG which has a dia of 1mm

CASE A - 5mm SPACING BETWEEN STUB CONDUCTORS:
S = 5mm, d=1mm
Hence ZSTB = 276 log10 (2S/d) = 276 log10 (2x5mm/1mm) = 276 log10 (10) = 276 x1 = 276 Ohms
Conclusion: Mismatch - 276 Ohms provided vs, 346 Ohms required

CASE B - 10mm SPACING BETWEEN STUB CONDUCTORS:
S = 10mm, d=1mm
Hence ZSTB = 276 log10 (2S/d) = 276 log10 (2x10mm/1mm) = 276 log10 (20) = 276 x1.301 = 359 Ohms
Conclusion: Matched closely - 359 Ohms provided vs, 346 Ohms required





.
Hello Ab cd,
I've 2 questions,i beg your pardon,I'm a newbie:
I would realize a Franklin collinear antenna , could diameter of conductor have effect on reception? I've some lenghts of internal copper conductor of coaxial cable Belden H 1000 type 2,62 mm diameter.....
Do you suggest to use another diameter?
What happens if i use a 50 ohm cable( Belden H 1000) instead of a 75 sat ohm cable?
thank in advance,kind regards and compliments for your work....
sergio
 

regast

New Member
Hi I have recently caught the ADS-B bug and this thread has been an EXCELLENT resource!! I have a few questions Im hoping ab cd or any other member can clear up.

ab cd, can you go into more detail about the 1075mhz coil in the splitter, what it does and how you calculated it? Im assuming it somehow filters signals, although its not a Hi Pass, Low Pass, or Band Pass... so how does it work and how do I make one for any frequency? Im intrested in filtering and running multiple antennas also! I will probably end up using RF relays in the end but this coil is very interesting.

Secondly I have built a CoCo antenna from rg6 it is on my roof. It has 2 quarter wave elements then 16 half wave elements and at the top it has another quarter wave the a brass tube quarter wave attached to the center conductor. I then have the whole thing connected to an LNA in the house (want to move to roof but thats a whole other project involving the RF relays). This is the performance im getting



I am very well versed in electronics but new to RF/SDR and Antenna design. Im wondering why I get such good range to the east but every other direction is fairly mediocre? Granted I live near mountains but I would think planes flying high above the ocean shouldn't be an issue? Id really like to get 300Km all the way around. Would 32 half wave elements be a nice improvement over 16? Im still trying to figure out how to add a choke or sleeve to decouple the antenna from the 30ft rg6quad shield feed line, not sure this is the answer to 300km though!
 

trigger

Member
Hi regast,
Interesting the CoCo you've built. Can we have a photo please? What lengths of coax did you cut? Myself and others have generally failed to build a decent CoCo. You must be doing something right!
 

regast

New Member
Ya no problem man, let me tell you the LNA I am using doesnt do much, Im not sure if thats becuase its not of the roof at the feed point or if its becuase the antenna already has so much gain.... well here are some unintresting pics... This is the CoCo in a 1 inch PVC structure, I use a 2 gallon bucket as a base with rocks on top to help keep it stable on the roof and resist the wind! Once I have perfected it I will be buying a tripod or putting slurry in the bucket!



Here Is a picture of the bare coax, which is mostly wrapped in electrical tape. I ran alot of continuity and resistance tests on it before tapping it up! It is very easy to make bad connections in the CoCo, that may be your problem; I had to untape and fix different sections like 10x, you shouldnt read more than 30 ohms from end to end on an array this big, and 15 or less ohms is probably closer to where you need to be... when I test the center to top I get like 3 ohms I think, and when I test the shielding to top shielding I get about 10 ohms.. You cant see it but the bottom is just an F connector that had been compression connected on, I reused old direct TV cables for the 2 bottom quarter waves.



And here is my topper, I have not tried it shorted yet, dont want to deal with decoupling the DC at this moment!



The topper is basically a half wave element, but I exposed a quarter wave of copper center conductor and soldered that brass tubing on to get some diameter. The exposed center conductor is also 6.8cm not 5.5 to make up for the coax velocity. The PVC cap only has the 6.8cm element sticking out.

Originally I had a copper clad ground plane soldered to the F connector which had 8 quarter wave 45 degree elements soldered to it. It seemed to help the antenna but I scrapped it because after I read more about dipoles it didn't make sense, and it would not physically work with the bucket base! Now im thinking that ground plan could have been acting as a balun???

So here is a pic I just drew maybe it will be helpfull

 

regast

New Member
Sorry I forgot to mention i have been drinking tonight so if some of that post is gibberish im sorry, just ask me to clarify! And I dont know if I mentioned it earlier but my CoCo is regular RG6, connected to a 20ft RG6 Quad Sheild Feed line connected to a power strip with coax in and out. I connected to the power strip to get an earth ground through the electrical system and hopefully stop lighting from hitting my LNA/SDR or PC...
 

ab cd

Senior Member
The inline amplifiers such as the one here http://www.ebay.co.uk/itm/IN-LINE-S...?pt=UK_Sound_Vision_Other&hash=item3ccdc6c614
does anyone know what sort of power they require (amps) and any recommendations for suitable power supplies (in UK) . I can find one psu rated at 14v but I think that's an off load rating, not sure what it would drop to on load - plenty of 12v psu's around
http://forum.planefinder.net/members/richard-lee.497/
Richard Lee
's reply is quiet comprehensive.

I just want to add that now there are state-of-the-art "switchable" type power supplies available. These are slightly costly, but are lighter (no iron-cored power transformer) and have much better regulation (i.e. off-load to full load voltage variation is very small). When searching on eBay, add word "switchable" in search sentence.

One more point: Some Amplifiers have a lower frequency limit of 47MHz. For some strange reason, these don't work at all on 1090 MHz, although their upper limit is much higher than 1090 MHz. Me & another forum member have faced this problem. Better be safe & buy one with lower limit around 950MHz.

My amplifier's rated power requirement is 25-40 mA, quiet low.
 

ab cd

Senior Member
Hello Ab cd,
I've 2 questions,i beg your pardon,I'm a newbie:
I would realize a Franklin collinear antenna , could diameter of conductor have effect on reception? I've some lenghts of internal copper conductor of coaxial cable Belden H 1000 type 2,62 mm diameter.....
Do you suggest to use another diameter?
What happens if i use a 50 ohm cable( Belden H 1000) instead of a 75 sat ohm cable?
thank in advance,kind regards and compliments for your work....
sergio
The diameter of wire affects:
(1) Imprdance of antenna
(2) Gap between wires of Impedance matching stub

There is practically no difference in performance of receiving*** antenna made of 1 mm or 2mm or 3mm dia wire, as long as each one is dimensioned according to the wire used. I used core of RG6 which is 18AWG wire dia 1mm. If you want to use 2.11 dia wire, or any other size, let me know. I will do calculations & computer simulation to get optimum dimensions. It is like purchasing a"Ready Made" suite vs "Tailor Made" suite.

For 1 mm dia wire, the optimum gap between matching stub wires is 2mm
For 2 mm dia wire, the optimum gap between matching stub wires is 3mm


Only wire dia counts, It does not matter you obtained the wire from a 75 ohm cable or from a 50 ohm cable.

==============================================================================================
***Receiving antennas handle power in milli & micro watts, hence even very thin wires are ok. Transmitting antennas handle power in hundreds or even thousands of watts & antenna has to be made of heavy gauge material to handle the large RF current.

Calculations (only for those who don't mind getting a headache trying to understated the theory/maths)

Based on dia of wire antenna impedance (before matching) usually ranges around 600 ohm for 1 mm wire & about 500 ohm for 2mm dia wire

Hence required impedance of Matching Stub Zstb = √(Zant x Zcab)
= √(600 x 75) = 212 ohms for 1 mm dia wire
and
= √(500 x 75) = 194 ohms for 2 mm dia wire

Stub Dimension calculation:
S= spacing between stub conductors (center-to-center)
d= dia of stub wire
G=gap between wires=S-d

Zstb = 276 log (2S/d)

which can be rearranged as
S = (d/2) x 10 to power (Zstb/276)
Hence gap G=S-d

Using d = 1mm and Zstb = 212 ohms,
S =1 x (1/2) x 10 to power(212/276) = 3mm
G=S-d=3mm-1mm=2mm

Using d = 2mm
Zstb = 194 ohms,
S =2 x (1/2) x 10 to power(194/276) = 5mm
G=S-d=5mm-2mm=3mm

 

ab cd

Senior Member
@ regast:
feeling sleepy (its late in night here), will reply in detail tomorrow. Quick reply below:
The coil is not a high-pass or low-pass filter. It is a "parallel resonant circuit" composed of coil's inductance & coil's self-capacitance.
It is a sort of cheap band-rejection filter, where center frequency of band = self resonant frequency of coil. The width of pass-band depends on Q of the coil: higher the Q, narrower the band. This is the famous "Tank Circuit" used to tune the radio receivers. Here it is used to reject 1090 MHz from passing to VHF antenna

Link to page from where I calculated inductance, self-capacitance & self-resonant frequency of my home-made coil
http://hamwaves.com/antennas/inductance.html

.Edit: Corrections shown in red
 
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regast

New Member
@ad cd, Lets take this scenario in to consideration. Lets say someone has two antennas on there roof, a CoCo or other design ADS-B antenna, and a discone. Now I know my CoCo receives FM/433mhz and 800mhz trunked systems loud and clear, much better than a set of rabbit ears with the filters removed. Now lets say the person were to add a 1090mhz coild as you did before the discone, this would make it so the ADSB antenna was the only one letting 1090mhz through, giving optimal ADS-B performance correct? But wouldn't the discone get loaded down with all the other out of band signals the CoCo antenna is receiving and cause problems for the discone? Do you get degraded air band reception with your set up than if you were to only run the air band and antenna by itself?
 

ab cd

Senior Member
@ad cd, Lets take this scenario in to consideration. Lets say someone has two antennas on there roof, a CoCo or other design ADS-B antenna, and a discone. Now I know my CoCo receives FM/433mhz and 800mhz trunked systems loud and clear, much better than a set of rabbit ears with the filters removed. Now lets say the person were to add a 1090mhz coild as you did before the discone, this would make it so the ADSB antenna was the only one letting 1090mhz through, giving optimal ADS-B performance correct? But wouldn't the discone get loaded down with all the other out of band signals the CoCo antenna is receiving and cause problems for the discone? Do you get degraded air band reception with your set up than if you were to only run the air band and antenna by itself?
There is a 1:9 ratio between air band frequency 120Mhz and ADS-B 1090 Mhz. The VHF antenna power will be fed to receiver, as well as the inLine amplifierks "out" port, which normally has high impedance to reverse feed. I did not notice any degradation of the airband signal by using this arrangement.
However since you want to use 433Mhz, which has only 1:2.5 ratio to ads-b frequency of 1090 Mhz, there may be degradation of 433Mhz signal. Why not to make a coil and give it a try?
 

ab cd

Senior Member
I am experiencing a contradiction in results I get by maths, by simulation, and by trial run of prototype.

Results of maths & simulations agree reasonably close, but when i run prototype, results are much poorer. I don't know why. This happens to Franklins, 5/8 wavelengths with phasing coils, etc.

There is another strange phenomenon with pepsi-can sleeved dipole. Without amp & connected directly by short piece of cable, it gives better results compared to franklin & 5/8 wavelength connected to same setup. With amp & long cable, franklin & 5/8 wavelength gives better results than pepsi-can sleeved dipole connected to same setup. Very strange.
 

ab cd

Senior Member
I am thinking loud about problem presented in my last post above.........

The tiny 1/2 wavelength dipole & pepsi-can sleeve dipole (which is also a 1/2 wavelength dipole) have an inherent impedance of 75 ohms, if both limbs are cut exactly 1/4 wavelength (69mm). This is easy to accurately achieve. Hence the prototype built by DIY, will have SWR very close to 1.

In the Franklin & 5/8 coil tuned antennas, the impedance is brought down to 75 ohms by stubs & coils. These are very sensative to accuracy, and a DIY built prototype will rarely have SWR close to designed SWR.

As a result of above, the1/2 dipoles perform better than franklin & 5/8 coil tuned antennas when used without Amplifier.

When used with Amplifier, the low SWR is compensated by the Amplifier, hence the stub & coil tuned antennas, which have gain of order of 6 dBi or mre, give better performance than 1/2 wavelength dipoles which have gain of order of 2.2 dBi.
 
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