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DarkPlatinum
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Antenna setup for aircraft signal advice

Sun Nov 11, 2018 11:00 pm

Hello, some of you might know that I am trying to get a raspberry Pi setup with tracking aircraft. I was wondering what tips and tricks you guys have to getting a better signal. My antenna is right at my window inside the house. I have unscrewed the antenna from the base, and trimmed it down to 68mm. I haven't been able to test its range as I am waiting for a adequate power supply to arrive.

Basically outside my house I have a old satellite dish that has not been used in years. If I was able to get the cabling working from it, would it be possible to use that as my antenna?
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drgeoff
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Re: Antenna setup for aircraft signal advice

Sun Nov 11, 2018 11:25 pm

DarkPlatinum wrote:
Sun Nov 11, 2018 11:00 pm
Basically outside my house I have a old satellite dish that has not been used in years. If I was able to get the cabling working from it, would it be possible to use that as my antenna?
No.

1. A satellite dish is highly directional. A few degree beamwidth.

2. Satellite dish has a LNB receiving signals in the 10-12 GHz approx. range. Not the 1 GHz approx that your 68 mm is optimised for.

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Idahowalker
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Re: Antenna setup for aircraft signal advice

Mon Nov 12, 2018 12:27 am

You can use the cable to the dish as a dipole antenna.

Determine the full. 1/2 an 1/4 length of wavelength of the frequency you'll be receiving. measure and mark the cable back from the end of either the full, 1/4 or 1/4 length. Carefully peel back the outer sheath to the marked distance and pull the inner sheath from the outer braided wire. You can cut the braided wire away from the cable; make sure it is a neat cut. The inner conductor becomes your antenna. The satellite dish can be taken in and used for other projects, like the base unit of a solar furnace.
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Re: Antenna setup for aircraft signal advice

Mon Nov 12, 2018 7:46 am

Idahowalker wrote:
Mon Nov 12, 2018 12:27 am
You can use the cable to the dish as a dipole antenna.

Determine the full. 1/2 an 1/4 length of wavelength of the frequency you'll be receiving. measure and mark the cable back from the end of either the full, 1/4 or 1/4 length. Carefully peel back the outer sheath to the marked distance and pull the inner sheath from the outer braided wire. You can cut the braided wire away from the cable; make sure it is a neat cut. The inner conductor becomes your antenna. The satellite dish can be taken in and used for other projects, like the base unit of a solar furnace.
Just say my wire was a 2 meters long, does this mean I pull back 68mm from each side? 68mm from I have heard is a quarter wavelength.
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Re: Antenna setup for aircraft signal advice

Mon Nov 12, 2018 8:11 am

DarkPlatinum wrote:
Mon Nov 12, 2018 7:46 am
Idahowalker wrote:
Mon Nov 12, 2018 12:27 am
You can use the cable to the dish as a dipole antenna.

Determine the full. 1/2 an 1/4 length of wavelength of the frequency you'll be receiving. measure and mark the cable back from the end of either the full, 1/4 or 1/4 length. Carefully peel back the outer sheath to the marked distance and pull the inner sheath from the outer braided wire. You can cut the braided wire away from the cable; make sure it is a neat cut. The inner conductor becomes your antenna. The satellite dish can be taken in and used for other projects, like the base unit of a solar furnace.
Just say my wire was a 2 meters long, does this mean I pull back 68mm from each side? 68mm from I have heard is a quarter wavelength.
It does not look like I can reach the tv satellite cable since it is being fed into the roof of my house. Would I be able to make an antenna with standard circuit/ electrical cable?
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jahboater
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Re: Antenna setup for aircraft signal advice

Mon Nov 12, 2018 10:30 am

DarkPlatinum wrote:
Mon Nov 12, 2018 8:11 am
It does not look like I can reach the tv satellite cable since it is being fed into the roof of my house. Would I be able to make an antenna with standard circuit/ electrical cable?
Yes, as a simple and cheap experiment. Don't expect it to perform as well as a purpose made antenna with the correct feeder cable!

You could just split the end of the cable (removing any cover) and separate the two cores for 68mm.
Hold the two arms apart somehow (cable tie them to a piece of wood perhaps), so that you have a T shape. Make sure the two arms are vertical.
This is a very crude 1/2 wave dipole antenna.
However, you are hoping to receive aircraft, so a dipole may not be best as it has a symmetrical, horizontal pattern.
It would receive aircraft near the horizon very well, but will not hear anything directly above.
A 1/4 wave antenna above a metal ground plane (a biscuit tin lid) will have an asymmetrical pattern pointing higher in the sky (30 degrees or so).

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Re: Antenna setup for aircraft signal advice

Mon Nov 12, 2018 11:31 am

jahboater wrote:
Mon Nov 12, 2018 10:30 am
DarkPlatinum wrote:
Mon Nov 12, 2018 8:11 am
It does not look like I can reach the tv satellite cable since it is being fed into the roof of my house. Would I be able to make an antenna with standard circuit/ electrical cable?
Yes, as a simple and cheap experiment. Don't expect it to perform as well as a purpose made antenna with the correct feeder cable!

You could just split the end of the cable (removing any cover) and separate the two cores for 68mm.
Hold the two arms apart somehow (cable tie them to a piece of wood perhaps), so that you have a T shape. Make sure the two arms are vertical.
This is a very crude 1/2 wave dipole antenna.
However, you are hoping to receive aircraft, so a dipole may not be best as it has a symmetrical, horizontal pattern.
It would receive aircraft near the horizon very well, but will not hear anything directly above.
A 1/4 wave antenna above a metal ground plane (a biscuit tin lid) will have an asymmetrical pattern pointing higher in the sky (30 degrees or so).
Interesting. I wonder how it would compare to the cheap small antenna that they give with the USB dongle. Would it be possible to add it on to the antenna given? The antenna that they gave, I have trimmed down to 68 mm.
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Idahowalker
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Re: Antenna setup for aircraft signal advice

Mon Nov 12, 2018 12:08 pm

I was going to add that instead of cutting the braided shield spread it out to form a ground plane. I saw the pie tine suggestion and thought 'Oi! great idea' to split the braided shield into 4 sections and spread unto the pie tin or other piece of metal; you might end u[p soldering the braid to the metal.

And the fellow is correct about not getting good reception on the straight above plane and thus another aspect of the project could be, with an attached ground plane, put the whole antenna onto a platform that can be pan and tilted with 2 servos.
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Re: Antenna setup for aircraft signal advice

Mon Nov 12, 2018 4:15 pm

Idahowalker wrote:
Mon Nov 12, 2018 12:08 pm
I was going to add that instead of cutting the braided shield spread it out to form a ground plane. I saw the pie tine suggestion and thought 'Oi! great idea' to split the braided shield into 4 sections and spread unto the pie tin or other piece of metal; you might end u[p soldering the braid to the metal.

And the fellow is correct about not getting good reception on the straight above plane and thus another aspect of the project could be, with an attached ground plane, put the whole antenna onto a platform that can be pan and tilted with 2 servos.
But using servos wont do much use if its indoors? Could i just solder a flat piece of metal to the existing antenna to get a better range? maybe 5cm x 5cm metal piece?
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Idahowalker
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Re: Antenna setup for aircraft signal advice

Mon Nov 12, 2018 6:31 pm

DarkPlatinum wrote:
Mon Nov 12, 2018 4:15 pm
Idahowalker wrote:
Mon Nov 12, 2018 12:08 pm
I was going to add that instead of cutting the braided shield spread it out to form a ground plane. I saw the pie tine suggestion and thought 'Oi! great idea' to split the braided shield into 4 sections and spread unto the pie tin or other piece of metal; you might end u[p soldering the braid to the metal.

And the fellow is correct about not getting good reception on the straight above plane and thus another aspect of the project could be, with an attached ground plane, put the whole antenna onto a platform that can be pan and tilted with 2 servos.
But using servos wont do much use if its indoors? Could i just solder a flat piece of metal to the existing antenna to get a better range? maybe 5cm x 5cm metal piece?
Range of reception will have some to do how well the antena is built and tuned to the receiving frequency, a pre-amp could help some, the strength of the transmission would help a lot, and, as well as a VSWR meter. But none of that will help with sensitivity of direction of received signal to a Di-pole antenna, sticking straight up.


Perhaps you have heard how someone lived close to a radio station boradcast antena and complaind about how terrible their reception was for that radio station?


Perhaps this may help you out: https://www.pulseelectronics.com/docs/l ... 7%2012.pdf

https://web.wpi.edu/Pubs/E-project/Avai ... paper2.pdf

Read this one first.
https://www.dxing.com/tnotes/tnote01.pdf
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Re: Antenna setup for aircraft signal advice

Mon Nov 12, 2018 7:47 pm

Hmm... I have found some internet cable or antenna cable in my shed from previous tenants living in my house. Would a longer antenna be better then a shorter antenna? Also does it matter how thick it is? (Providing the length of the antenna is 1/4, 3/4, 1 and 1/4, 1 and 3/4 wavelength and so on.)
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jahboater
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Re: Antenna setup for aircraft signal advice

Mon Nov 12, 2018 8:36 pm

DarkPlatinum wrote:
Mon Nov 12, 2018 7:47 pm
Would a longer antenna be better then a shorter antenna?
Wow - a *big* question!
Talking about omni-directional vertical antennas (briefly) ....
The captured signal goes up with the square of the length.
However, the antenna must be a correct fraction of the wavelength for the frequency of interest, or sometimes multiples thereof.
As you add multiples (5/8, 2x5/8, 3x5/8 say), the gain increases and the antenna becomes more directional.
This is a bad thing for scanning the skies!

In free space, a dipole pattern looks like a ring donut. The antenna goes up the middle and the maximum reception is at right angles to it (you can see why you get no reception at all either straight up or straight down).
A higher gain antenna is like a squashed, flatter, wider donut.

I would stick with 1/4 wave or 1/2 wave. (actually a 1/4 wave is really a 1/2 wave with the lower half being the ground plane, or for a hand-held radio, the chassis of the radio and the operators arm!)
Antennas have a particular impedance which should agree with that of the feeder cable and so on.
1/4 wave and centre fed 1/2 wave antennas have a conveniently reasonable impedance (for example a 1/2wave is about 73 ohms, and a 1/4 wave is around 50 ohms depending in the shape of the ground plane or radials).
Anything thing else needs extra bits added (a 5/8 wave needs a coil, an end fed half wave or a 2x5/8 wave, needs a transformer and so on).

The presence of a large metal plate below the antenna (such as a car roof) pushes the pattern upwards, which in your case is a good thing.
DarkPlatinum wrote:
Mon Nov 12, 2018 7:47 pm
Also does it matter how thick it is?
The thickness makes a very slight difference. A thicker antenna will receive a wider range of frequencies, and might be slightly shorter.
Not worth thinking about.

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Re: Antenna setup for aircraft signal advice

Mon Nov 12, 2018 10:40 pm

Thanks for your help so far. Which do you advise me to use, a 1/4 wavelength or 3/4 wavelength? I would just and the extra 2/4 wavelength onto my existing antenna (single pole). I can't really create my own antenna as I do not have and MCX connector. All I can really do is make my existing antenna long and thicker possibly.

Would you recommend 3/4 wavelength antenna with some aluminium foil layers on top as a flat surface?
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jahboater
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Re: Antenna setup for aircraft signal advice

Mon Nov 12, 2018 10:58 pm

DarkPlatinum wrote:
Mon Nov 12, 2018 10:40 pm
Thanks for your help so far. Which do you advise me to use, a 1/4 wavelength or 3/4 wavelength? I would just and the extra 2/4 wavelength onto my existing antenna (single pole). I can't really create my own antenna as I do not have and MCX connector. All I can really do is make my existing antenna long and thicker possibly.

Would you recommend 3/4 wavelength antenna with some aluminium foil layers on top as a flat surface?
You cant just do things like that.
There needs to be junction between the sections that changes the phase by 180 degrees (a coil or a capacitor).
The only simpler commonly used configuration is 5/8 (1/2 + 1/8) that doesn't require a phasing junction, and that works in a completely different way from the others. 5/8 requires a very large reflective metal surface below it - the out of phase lower 1/8 part bounces off the metal and rejoins the main signal having changed its phase in the process. Even that needs a matching coil at base.
Its complicated. Honestly just try a basic dipole!
The old Pi3 antenna was a dipole!

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Re: Antenna setup for aircraft signal advice

Tue Nov 13, 2018 8:20 am

jahboater wrote:
Mon Nov 12, 2018 10:58 pm
The old Pi3 antenna was a dipole!
But the antenna is only 68mm long in one direction? This is what my antenna looks like:

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Re: Antenna setup for aircraft signal advice

Tue Nov 13, 2018 8:56 am

DarkPlatinum wrote:
Tue Nov 13, 2018 8:20 am
jahboater wrote:
Mon Nov 12, 2018 10:58 pm
The old Pi3 antenna was a dipole!
But the antenna is only 68mm long in one direction?
The Pi3 antenna was for 2.4GHz. Frequency * Wavelength == 299792458

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Re: Antenna setup for aircraft signal advice

Tue Nov 13, 2018 9:47 am

jahboater wrote:
Tue Nov 13, 2018 8:56 am
DarkPlatinum wrote:
Tue Nov 13, 2018 8:20 am
jahboater wrote:
Mon Nov 12, 2018 10:58 pm
The old Pi3 antenna was a dipole!
But the antenna is only 68mm long in one direction?
The Pi3 antenna was for 2.4GHz. Frequency * Wavelength == 299792458
So the original antenna was 2.4 ghz, i trimmed it to 68mm which is 1/4 wavelength. How can i make a di pole from this existing antenna if it is just an antenna in 1 direction.
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jahboater
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Re: Antenna setup for aircraft signal advice

Tue Nov 13, 2018 10:24 am

DarkPlatinum wrote:
Tue Nov 13, 2018 9:47 am
jahboater wrote:
Tue Nov 13, 2018 8:56 am
DarkPlatinum wrote:
Tue Nov 13, 2018 8:20 am

But the antenna is only 68mm long in one direction?
The Pi3 antenna was for 2.4GHz. Frequency * Wavelength == 299792458
So the original antenna was 2.4 ghz, i trimmed it to 68mm which is 1/4 wavelength. How can i make a di pole from this existing antenna if it is just an antenna in 1 direction.
I just gave the Pi3 as a common example of a dipole. (I don't yet understand exactly how the new antenna on the Pi3B+ works)

You have all the info you need above!

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Re: Antenna setup for aircraft signal advice

Tue Nov 13, 2018 10:42 am

No no, thats not what i mean, what i meant is, on my existing ADS B antenna, its just a stick antenna, how can i convert that into a dipole antenna? I don't know much about antennas. I got confused when you started talking about a Pi 3 antenna, i thought you were talking about my antenna not the wifi chip antenna (i think thats what your talking about?)
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drgeoff
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Re: Antenna setup for aircraft signal advice

Tue Nov 13, 2018 2:08 pm

There is plenty of info on the net about making all kinds of aerials for aircraft tracking. Simplest to make dipole is probably the cork and two bits of stiff wire one.

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Re: Antenna setup for aircraft signal advice

Tue Nov 13, 2018 3:25 pm

drgeoff wrote:
Tue Nov 13, 2018 2:08 pm
There is plenty of info on the net about making all kinds of aerials for aircraft tracking. Simplest to make dipole is probably the cork and two bits of stiff wire one.
Yes I have looked online, but many of them require buying an mcx connector to attach to the reciever dongle. I would like to modify my exisitng antenna without having to buy extra parts. I do have some antenna cable that i have unsheathed.
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Re: Antenna setup for aircraft signal advice

Tue Nov 13, 2018 3:54 pm

DarkPlatinum wrote:
Tue Nov 13, 2018 10:42 am
No no, thats not what i mean, what i meant is, on my existing ADS B antenna, its just a stick antenna, how can i convert that into a dipole antenna? I don't know much about antennas. I got confused when you started talking about a Pi 3 antenna, i thought you were talking about my antenna not the wifi chip antenna (i think thats what your talking about?)
I think jahboater was talking about the wifi chip antenna, although I'm not sure it's a dipole as normally the chip antennas only have a single connection - a dipole has two elements (di meaning two).

You can't really convert the small antennas you get with the rtlsdr/tv dongles into a dipole. If you really wanted to do that cut the antenna part off and just use the coax ends, but before doing that read on ...

Taking a step back, two things which will likely make the biggest difference are getting the antenna portion outside and as high up as possible. The better the view of the sky it has the more it'll receive. Anything that can block the signal (which can include glass) will limit what the antenna can pick up.

Going for a basic bit of theory. The frequency and wavelength are related by the speed of light. In a simplified form: 300 / Frequency (MHz) = Wavelength (m). So for ADSB with a frequency of 1090MHz you have a wavelength of 0.275m. Typically the driven element in a ground plane antenna or each part of a dipole antennas will be a 1/4 wavelength (so 0.0688m or 68.8mm).
DarkPlatinum wrote:
Tue Nov 13, 2018 3:25 pm
Yes I have looked online, but many of them require buying an mcx connector to attach to the reciever dongle. I would like to modify my exisitng antenna without having to buy extra parts. I do have some antenna cable that i have unsheathed.
I wouldn't recommend trying to attach an mcx connector to coax cable you'll almost certainly need a suitable crimp tool, soldering iron and a lot of patience. An easier approach is to get a suitable pigtail so you can then make an antenna and feeder cable using more suitable parts and plugs (BNC is probably the easier plug to start with). In terms of antenna I'm wondering if something like a QFH, halo, or crossed dipoles might be better designs. These might give a better coverage above the antenna. The groundplane and dipole antenans will have very similar patterns and (for a vertical antenna) will be good towards the horizon but poor for anything above.

In terms of connecting the antenna to the dongle you want to get the best coax you can (especially for longer runs). Satellite coax is generally reasonable the stuff that comes with those small antennas isn't so great (around 1dB/m at 1GHz). What is often sold as Low Loss TV coax (at least in the UK) really only belongs in the metal skip.

If you want to learn lots more about antennas there are several good books around particularly look at those from the ARRL or RSGB (or ones those organisations suggest).

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Re: Antenna setup for aircraft signal advice

Tue Nov 13, 2018 3:57 pm

--------------
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Re: Antenna setup for aircraft signal advice

Tue Nov 13, 2018 4:14 pm

Definitely, 1st and 2nd link is what I need; tips for better antenna performance. 3rd link not so much but a good read nevertheless
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