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Thread: Newbie on Raspberry Pi and DVP-T USB wants to set up an external antenna

  1. #1
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    Newbie on Raspberry Pi and DVP-T USB wants to set up an external antenna

    Hi kind folks here.

    Completely new to plane tracking and my very first post here. Just set up my Raspberry Pi yesterday and set it up with an entry-level DVB-T USB stick (with its antenna). Photos attached here. I started feeding data to FR24, but being an indoor antenna it has it limitations. So I am looking to set up an external antenna which I will place on the top of the building.

    51Ny4caYpRL._SL1024_.jpg

    antenna.jpg

    I am looking to set up an external antenna via a Coaxial cable.

    Can you folks please guide me how to go about it?

    1) Please suggest an external antenna which is easy to make (DIY) . Alternatively, I can purchase one .

    2) Can I connect an external antenna to the USB stick using a 12 meters coaxial cable?

    3) I am guessing I will have to crimp a MCX male connector at one end of the cable (which will go into the USB stick).

    Thanks in advance guys.

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    Did you happen to have a poke around the forum beforehand?

    Theres a section dedicated to such questions with a couple of really good threads already

    Start at the end and work backwards on this one
    https://forum.flightradar24.com/thre...1-best-antenna

    And for DIY...
    https://forum.flightradar24.com/thre...g-No-Connector

    What you need is low loss cable (this is microwave) and pigtail. Rubbish cable and crimping will usually bring greater issues
    Posts not to be taken as official support representation - Just a helpful uploader who tinkers

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    Quote Originally Posted by Oblivian View Post
    Did you happen to have a poke around the forum beforehand?


    What you need is low loss cable (this is microwave) and pigtail. Rubbish cable and crimping will usually bring greater issues
    Thanks for the link. I will try a simple DIY first. I did read up some of the links before posting, but the plethora of information can be overwhelming at times. :-)

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    Hi,
    I am also Newbie on Raspberry Pi and DVB-T USB.
    I connect a HDTV USB DVB-T to rpi2b with raspbian.
    Please let me know if this device also can be used for feeding?
    Thanks,
    HDTV USB DVB-T.jpg

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    Quote Originally Posted by duvid View Post
    Hi,
    I am also Newbie on Raspberry Pi and DVB-T USB.
    I connect a HDTV USB DVB-T to rpi2b with raspbian.
    Please let me know if this device also can be used for feeding?
    Thanks,
    HDTV USB DVB-T.jpg
    You just plain can't tell from the outside. It's what is on the inside that counts.

    Only way to tell is get dump1090 and see (before registering to fr24 and finding it does not)

    Sent from my XT1092 using Tapatalk
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  6. #6
    Flight attendant Strix technica's Avatar
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    Quote Originally Posted by johy View Post
    I started feeding data to FR24, but being an indoor antenna it has it limitations.
    You might be surprised what a good, indoor antenna (but still placed as high as possible, eg in the loft) can do. That's where mine is and I was getting max 100–130 nm avg 50 nm. With a decent LNA and filter (such as the FA Pro stick +, though doubtless you can do better still if you buy good quality discrete parts), that went up to max 213nm, avg 96 nm.

    Quote Originally Posted by johy View Post
    So I am looking to set up an external antenna which I will place on the top of the building.

    I am looking to set up an external antenna via a Coaxial cable.

    Can you folks please guide me how to go about it?
    Height definitely helps, but a rubbish antenna 10m above your roof won't perform as well as a good quality antenna at soffit level or even in the loft. Remember, most of the signals come from significant elevation (compared with terrestrial signals such as TV and radio) with only the farthest coming from the horizon. That extra 10m won't make any difference to the horizon, and obstructions (eg neigbours' roofs) only matter for a/c directly on the horizon.

    The main reason for mounting the antenna outside is to get it clear of the attenuation of your own roof (which is close enough that it does matter). For that reason, an outside antenna that is mounted at the side of the house or isn't clear of the peak of the roof isn't much better than an antenna inside.

    The whip antenna supplied with your DVB is rubbish for ADS-B (although mine did better than I would have expected). Even a properly tuned whip or dipole won't perform as well as a co-linear (talked about at length in this forum and elsewhere) because neither can get the gain† of a co-linear nor have the collecting surface area of a co-linear.

    You can build your own co-linear and a basic version only requires coax, a knife, some tape, patience — and accuracy. The co-linear is not a forgiving design, so depending on your skill, appetite for experimentation and tolerance of frustration, you might be better off buying the antenna.

    Quote Originally Posted by johy View Post
    1) Please suggest an external antenna which is easy to make (DIY) . Alternatively, I can purchase one .

    2) Can I connect an external antenna to the USB stick using a 12 meters coaxial cable?

    3) I am guessing I will have to crimp a MCX male connector at one end of the cable (which will go into the USB stick).

    Thanks in advance guys.
    First, USB is officially limited to about 5 metres. You can do 10 metres if you put a powered hub in between two 5 metre cables, but that isn't going to work for you. There are various other types of USB extender with a longer reach, but good luck with those.

    Coax is a different animal altogether. There are many different types and of each, there is a huge range of quality of construction.

    First, there's 75Ω vs 50Ω. Your receiver is 75Ω so, in theory, you should use 75Ω coax. In practice, the impedance mismatch loss with 50Ω is only about -0.18 dB. Cable attenuation is a bigger deal.

    Apropos, different types (and even different makes) of coax have different loss characteristics. Nominally, RG6 and RG59 are both 75Ω coax, but have -2 and -2.65 dB/10 metres @ 1000 MHz respectively. RG8 and RG58 are both 50Ω coax and have -4.5 and -7 dB/10 metres @ 1000 MHz respectively. Note that these are nominal figures. Actual loss depends on quality of cable. Your average CATV RG6 coax is crap quality and will probably be a lot noisier and higher loss than those figures quoted above.

    Also note that attenuation loss is much greater than mismatch loss.

    Your best bet is to use good quality RG6, a good quality LNA (low noise amplifier)† and a 1090 MHz band-pass filter. FlightAware sells the latter. If you put the filter between the antenna and LNA as close to the antenna as you can, coax losses become much less of a problem because the amp provides all the power required to drive even a long run of coax.

    Note that masthead amps require a DC injection box which adds a complication, but it's your only option if you've got a long coax run to your receiver.


    † The term 'gain' is used with both antennae and amplifiers, but they mean different things.

    An antenna is a passive device. It cannot increase absolute signal, but it can confine its sensitivity to a particular pattern which has the effect of increasing its sensitivity in the pattern at the cost of sensitivity out of the pattern.

    That means, for example, that a 12 dBi antenna is not necessarily better than a 5 dBi antenna. The 12 dBi whip will reach further (typically to the horizon), but will pick up less as altitude increases. Terrestrial TV antennae are an example of this: even so-so ones can be 10-15 dBi, but they're intended to be so directional that they pick up only signals from the direction at which the antenna is pointed. Satellite dishes are even more pronounced: they can have gains of around 40+ dBi, but they are even more sensitive to alignment because their pattern is so tight.

    Amplifier gain is literally an increase in the absolute signal. Everything comes at a cost, though, and this time it's an increase in the noise. That's why you put the bandpass filter between the antenna and LNA so's to minimise the noise that is amplified and sent down the cable.

  7. #7
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    Hi,
    if i do localhost:8754
    and get:
    Flightradar24 Feeder/Decoder
    Linux/generic/static_arm/1.0.18-9
    Updated: 21:20:52 GMT+0300 (IDT)
    FR24 Link: Connected via UDP
    FR24 Radar Code: T-LLHA4
    Aircraft Tracked (ModeS & ADS-B): 0
    Aircraft Uploaded: N/A
    Receiver: dvbt, Connected
    MLAT running: NO

    I amuse that this is OK to start tracking?

  8. #8
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    That's the output from fr24feed and if that's running, then you're already connected and feeding.

    Aircraft Tracked (ModeS & ADS-B): 0
    But that suggests that something is wrong with your antenna...

  9. #9
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    Quote Originally Posted by duvid View Post
    Hi,
    if i do localhost:8754
    and get:
    Flightradar24 Feeder/Decoder
    Linux/generic/static_arm/1.0.18-9
    Updated: 21:20:52 GMT+0300 (IDT)
    FR24 Link: Connected via UDP
    FR24 Radar Code: T-LLHA4
    Aircraft Tracked (ModeS & ADS-B): 0
    Aircraft Uploaded: N/A
    Receiver: dvbt, Connected
    MLAT running: NO

    I amuse that this is OK to start tracking?
    As above that is why I suggested something such as dump1090 or rtl1090 to confirm if that stick is capable.

    Chances are that USB stick does not have the right chipset available (without seeing it) or no range.

    You will need to do more testing with commands to see what is displayed on startup, not the config page

    sudo fr24feed service stop
    sudo fr24feed start
    and look for errors

    Or stop all and run
    rtl_test

    You need to see the right output, not errors as shown
    https://forum.flightradar24.com/thre...ll=1#post74834
    Posts not to be taken as official support representation - Just a helpful uploader who tinkers

  10. #10
    Flight attendant Strix technica's Avatar
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    Or, as a last resort, run rtl_tcp and use SDR# to see whether you can pick up commercial FM radio. if you can't do that much, you know that something is hosed.

    Also check that the USB device isn't locked by a kernel driver (look at lsusb and lsmod). Running any of the rtl_* commands (including rtl_test) will tell you if it can't attach to the device.

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