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Discussion in 'Antennas, Filters etc' started by Mukundan, May 3, 2013.
Can some one post a easy to build ADS-B Antenna with pre-amp design ?
The reception at 1090 MHz is line-of-sight, and is restricted to about 450 km due to curvature of earth. The most important thing is to locate antenna up and clear of obstruction. Also, since the planes are in all directions, an omni-range (covering 360 degrees) should be used.
I have built a very simple and tiny home-designed, home-made omni-directional antenna which gives me 450 km range with 2 in-line amplifiers, 18 dB Gain each (costing about $4 each amplifier). The antenna is a simple dipole, each arm being 6.8 cm long (quarter wave at 1090 MHz) . Please see pictures below showing the home-brew antenna and associated equipment(2 in-line amplifiers, Bias-T (15V DC power injector)+Demuxer to combine 1090 MHz antenna with FM/Air-band whip antenna (60cm long).
PHOTO 1 OF 2
PHOTO 2 OF 2
Hope this is helpful.
The 1/2 wave dipole with a dimension of mere 2 x 1/4 wavelength legs is 2 x 6.8 cm or total of 13.6 cm tall.
This is really tiny & cute antenna.
However, I have built a larger antenna which is 4 times taller than the tiny-cute 1/2 wavelength dipole.
It is a dipole, each leg consists of 2 1/2 wavelength element, making it total 4 x 13.6 cm = 54.4 cm tall.
It is called Franklin Co-Linear Dipole Antenna.
Attached 3 pictures show:
(1) 4-Element Franklin Co-Linear Dipole Antenna
(2) Coverage using Franklin Antenna
(3) Reciever DVB-T SDR USB Dongle connected to Desktop Computer.
PICTURE 1 OF 3 - FRANKLIN CO-LINEAR ANTENNA
PICTURE 2 OF 3 - COVERAGE
PICTURE 3 OF 3 - RECEIVER
Hope this will be useful
AFFECT OF HEIGHT OF ADS-B RECEIVING ANTENNA ON THE RANGE:
Height of ADS-B Receiving Antenna does NOT appreciably affect the Range.
In case of Ground-to-Ground Communications at UHF/Microwave, the heights of both the receiving and transmitting antennas greatly affect the range.
In case of Air-to-Ground ADS-B Communications, the Transmitting antenna is on the Aeroplane, which is several thousand feet high. The contribution of height of receiving antenna to the overall range is therefore not appreciable.
The range is combination of ranges of transmitting & Receiving antennas.
Overall Range = Range of Transmitting Antenna + Range of Receiving Antenna
= 1.41 x √h1 + 1.41 x √h2 miles,
h1 = height of transmitting antenna in feet.
h2 = height of receiving antenna in feet.
Based on these formula, I have calculated the Range for various heights of Receiving Antenna and Airplane, and have tabulated the results. These results show that increasing height of RECEIVING Antenna from 25 to 200 feet does not appreciably affect the overall range of ADS-B.
PLEASE SEE ATTACHED PICTURE BELOW for the tabulated results:
Most antenna books & sites discuss TRANSMITTING antennas. The TRANSMITTING antenna is intended to radiate electromagnetic waves into space. For Transmitting antenna, the most important criteria is that the antenna should be capable to radiate in space ALL the power which the transmitter can deliver.
What we need for ADS-B is a RECEIVING antenna. The RECEIVING antenna is not intended to radiate power. Its function is to intercept the electromagnetic waves radiated by transmitting antennas, and feed this intercepted power into coaxial cable & receiver. For Receiving antenna, the most important criteria is that it should intercept maximum amount of electromagnetic radiation, and then efficiently transfer it to the receiver.
For maximum transfer of power from transmitter to antenna and then from antenna into space, the impedance of the transmitter, the antenna and the transmission line (coaxial cable connecting the transmitter to the antenna) must be the same. The antenna is called "RESONANT" or "TUNED" if this is achieved. Transmitters typically are designed for 50 Ohms impedance, and the coaxial cables (transmission lines) used with them also have 50 Ohms impedance. Some antenna configurations often have an impedance other than 50 Ohms and impedance matching circuit is then required to transform the antenna impedance to 50 Ohms.
For Transmitting antennas, another way to measure the extent of power transfer is Standing Wave Ratio (SWR or VSWR). A VSWR of 2.0:1 or less is often considered acceptable. Most commercial antennas are specified to be 1.5:1 or less. Based on a 100 watt transmitter, a 1.5:1 VSWR equates to a forward power of 96 watts and a reflected power of 4 watts, or the reflected power is 4.2% of the forward power.
The most important criteria for RECEIVING antenna is therefore to intercept maximum amount of electromagnetic radiation, and then efficiently transfer it to the receiver. Larger the physical size (length) of antenna, larger amount of Electromagnetic radiation it will intercept and produce larger amount of power to feed to the receiver. Impedance matching results in maximum transfer of power from antenna to receiver, but this can be achieved by matching circuits or matching transformers (balun). There is no need to limit the size of receiving antenna to 1/2 wavelength just to achieve "RESONANCE", and thus limit the intercepted power.
A short 1/2 wavelength Dipole (or 1/4 wavelength Monopole with ground plane) is a reasonably good solution for TRANSMITTING antenna, but is not so good for receiving antenna due to its short length limits the interception of amount of available electromagnetic radiation. A larger antenna with impedance matching circuit/balun give better received signal strength.
If you want a simple and very quick antenna project I recommend this. Construction guide for a simple ADS-B antenna project.
It took me about 45 mins using stuff I had laying around. I did substitute a common 1" flat washer to use as the mount, I drilled out the existing hole to fit a standard TV coax connector usually sold with a plastic wall mount - it has the washer and nut to secure it. I roughed up the washer surface and flashed it with solder ready to accept the radials.
I had low expectations, the whole thing is only about 4-1/2 high and wide. I attached it to a short piece of 50 ohm coax. It provides me 80 to 100 NM receiving range and sometimes more--even indoors on a second floor. This is not stellar of course but it sure beat out the stock little mag mount that came with the dongle. If nothing else it whet my appetite to homebrew antennas and experiment. The price was right at zero and it is a good spare portable set up as it is so small.
COMPARISON OF COVERAGE OF FOUR (4) DIFFERENT ANTENNAS
WITHOUT AMPLIFIER and very short coaxial cable (11 feet / 3.5 meters) between Antenna & Receiver
(Tests results for these antennas WITH Amplifier will be posted when completed).
1) DIPOLE: 1/2 WAVELENGTH
2) FRANKLIN DIPOLE: 1/2-OVER-1/2 WAVELENGTH
3) COAXIAL COLLINEAR: 3-AND-1/2 ELEMENTS (EACH ELEMENT 1/2 WAVELENGTH) WITH SHORTED TOP
4) COAXIAL COLLINEAR: 3-AND-1/2 ELEMENTS (EACH ELEMENT 1/2 WAVELENGTH) + 1/4 WAVELENGTH WHIP
Coaxial Collinear 1/2 wave element =1/2 x wavelength @ 1090 MHz x coaxial cable velocity factor
For RG6 cable with FPE (Foamed PolyEthylene) insulation, velocity factor = 0.8
Coaxial 1/2 wave element =1/2 x 27.5 cm x 0.8 = 11 cm
Tests Results for these antennas WITH Amplifier will be posted when completed.
COMPARISON OF COVERAGE OF TWO (2) DIFFERENT ANTENNAS WITH AMPLIFIER and very short coaxial cable (11 feet / 3.5 meters) between Antenna & Receiver
1) COAXIAL COLLINEAR: 3-AND-1/2 ELEMENTS (EACH ELEMENT 1/2 WAVELENGTH) WITH SHORTED TOP
2) COAXIAL COLLINEAR: 3-AND-1/2 ELEMENTS (EACH ELEMENT 1/2 WAVELENGTH) + 1/4 WAVELENGTH WHIP
TEST SETUP - CoCo (Coaxial Collinear) With SHORTED TOP + AMPLIFIER
SEE 200 pF DC BLOCKING CAPACITOR (BETWEEN ANTENNA & AMPLIFIER) IN PICTURE 4
PICTURE 1 of 5
PICTURE 2 of 5
PICTURE 3 of 5
PICTURE 4 of 5
Picture 5 of 5
FRANKILIN ANTENNA WITH IMPEDANCE MATCHING STUB
1/2 wavelength-over-1/2 wavelength Dipole
400 KM Maximum Range WITHOUT Amplifier!!!!
See pictures below:
Picture 1 of 5
Picture 2 of 5
Picture 3 of 5
Picture 4 of 5
Picture 5 of 5
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
Image 2 of 3 - Coverage with 10mm spacing of Stub Conductors
THEORY & CALCULATIONS
Image 3 of 3 - Calculations
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
Matching for end-fed co-linears
Has anyone experimented with matching for end-fed co-linears. I have built 8 1/2 wavelength elements and 21 1/2 wavelength element co-linears using RG59 with copper braid without shorting the end and received typical ranges shown here in the pictures. Performance wise, the 8 element comes closer to a commercial Bulgarian 5DB reference antenna I use but doesn't quite measure up when looking at the captured message rate. Range wise the 5DB reference antenna has about 50 nm more range than the 8 element co-linear.
The impedance of an end-fed coaxial collinear antenna is same as the coaxial cable of which it's sections are made of. Since you have used RG59 cable which has an impedance of 75 ohms, the impedance of antenna is also 75 ohms. If your receiver has 75 ohm input, and you are using a 75 ohm cable (RG59 or RG6) to connect receiver to antenna, then you have a perfectly matched system & don't need any method or device for impedance matching.
Franklin collinear center fed dipole required matching because it's impedance is 1600 ohms, while my receiver (DVB-T USB Dongle) and connecting cable both have an impedance of 75 ohms, a gross mismatch.
What is the length of elements in the antennas you have built?
Use a shorted top 1/2 element, and it will markedly improve your range. Most of commercial antennas have shorted top.
Note: If you are using an inline amplifier, then you have to insert a dc blocking capacitor between antenna & amplifier, else the dc power supply to amplifier will get damaged due to short at top of antenna
I've been looking at this thread for some time with a great deal of interest, as I've been looking for an ADS-B antenna with a good bit of gain for a good while.
This afternoon I got some time and made an EZNEC (antenna modelling software) model of your open-stub Franklin Collinear Dipole.
Very impressive! As shown, you've come very close to a 1.5:1 SWR (into 75 ohms) and with some minor tweaks of the feedpoint position and the length of the matching sections, that can be reduced to about 1.2:1. With the tweaks, it has a predicted 10.5 dBi gain at 1.8 degrees elevation, which I believe is proper for an ADS-B antenna.
In the next few days, I intend to build one and will let you know how it goes and how it works out.
thanks much and 73,
1. Thanks for modelling and sharing info.
2. May I know the minor tweaks to improve VSWR to 1.2:1?
3. Can you please do a favour and model the franklin with shorted stub, 10mm spacong between stub conductors?
4. Are yoy an Amature Radio Operator, as indicated by your nick name "KD5 BYB" which resembles a call sign? 73
Element lengths for the .66 velocity factor cable I used was 9.1 CM.
I have taken them down and opened them up to solder the top end quarter wave piece and add the 200 pf cap in series with the feed line center conductor.
I have the preamps ordered but having difficulty sourcing the 4.7 mil-henry choke here locally.
These candidates are for my farm 600 ft up the mountain on a combination 50 ft hardwood tree and a 50 ft bamboo mast attached. I would like to get the performance out of the 8 element co-linear that I get with the reference antenna here at the QTH.
Thanks for your work there.
Here is my potential coverage from the farm: http://www.heywhatsthat.com/?view=FHLIAH5C
1) Inductor is not 4.7 milli Henry. It is 4.7 micro-Henry.
2) Inductor value is not critical. You can use any value from 1 micro-Henry to 10 micro-Henry. I have made 2 power inserters, one with 3.3 micro-Henry Inductor, other with 4.7 micro-Henry inductor. Both work equally good.
Try this Link for purchase of inductor on eBay:
....Here is This Week's Top 4 Stubs Chart .....
(ALL WITHOUT AMPLIFIER)
At Number 4 is : 5 mm spacing, Open-ended stub
At Number 3 is : 5 mm spacing, Short-circuited stub
At Number 2 is : 10 mm spacing, Open-ended stub
And at Number 1, The WINNER is : 10 mm spacing, Short-circuited stub
No thanks needed - I'm new to EZNEC and this was a great opportunity to learn some of its features. Up until buying EZNEC, I had been evaluating my ADS-B antennas in the same fashion as you have been doing - maximum range evaluation. Here at my house, plane traffic varies greatly from day to day, so to get a good comparison between antennas, I've got to set up an antenna and let it run for a week or so before being confident I can compare the results. It appears that your location has a *lot* more airplane traffic, so you may not have to wait as long to have repeatable, comparable results. With EZNEC, I plan to model the designs, tweak the model, then do the maximum range comparison as the final test.
I'll be happy to share my tweaks, but I want to do two things before I do that. First, I need to double-check my model, as I think I may have an error in how I created the model of the stub itself. In my model, instead of keeping the stub length constant and moving the connection of the coax on the stub, I connected the coax at the end of the stub and varied the length of the stub. While the end result is still good, it may or may not represent the design you have presented. Second, I want to create a drawing of the antenna with the tweaks. While I think I can describe the tweaks in words without an issue, a picture will really make things clear. I would also like to show the antenna patterns predicted by EZNEC, as this antenna has a very directional response in elevation that I believe is very favorable for ADS-B reception. I may not be able to do this until this weekend, unless things are work calm down a little bit.
I'll be happy to model the shorted stub Franklin with 10mm spacing. If I'm looking at the diagrams correctly, the dimensions between the 10mm open stub version and the 10mm closed stub version are the same, with the only difference being the closed end to the stub. I will double-check this before I finish the models.
I am indeed an amateur radio operator, callsign KD5BYB.
thanks much and 73,