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Thread: Raspberry PI Dual tuners

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    Raspberry PI Dual tuners

    Afternoon all,

    Does anyone know if its possible to put two tuners into the PI and use the feed from both.?
    I want to run two tuners 1 using a co-lin antenna and the 2nd from a high gain yagi.

    Any thoughts.?

    Regards

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    use modesdeco2 to "read" both sticks then connect fr24 feeder to modesdeco2. If I got you right.
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    Quote Originally Posted by rangler View Post
    Afternoon all,

    Does anyone know if its possible to put two tuners into the PI and use the feed from both.?
    I want to run two tuners 1 using a co-lin antenna and the 2nd from a high gain yagi.

    Any thoughts.?

    Regards
    Why not just use the antenna that has the best signal strength?
    Good question though. No problem connecting and installing two receivers on raspberry pi but don't know if you could feed two tuners to fr24feed.
    Last edited by Sam26K; 2016-01-18 at 05:17.

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    For me and after being shown a big parabolic dish im thinking of 4 to make 360* cover and all to feed one dongle into one Pi.

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    That idea sounds interesting. Need a mixer and maybe an LNA at the antenna end to overcome the loss of the mixer and cable.
    My initial design is somewhat crude right now, but I have one of those 6dB gain co-linears from FlightAware and designing to have the dongle and raspberry pi mounted directly on the mast to eliminate the loss from a long run of coax. Using Wifi and headless configuration so the only long wire to the antenna is the 120VAC extension cord for the pi's ac adapter.

    I still need to invest in an outdoor enclosure and lightening protection for everything before I take it outside but even indoors I'm getting over 125 mile range so far.

    Edit: On the 120VAC issue of running it up an antenna mast (not safe) it could also be done with a safer voltage such as 24VAC with the appropriate power converters.
    Last edited by Sam26K; 2016-01-19 at 09:22.

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    If you use decent power cable for outdoors it'll be fine. SWA is perfect for this.

    I run my pi via POE at the top of the mast.

    No hardware needed from the understanding. It's all software based so you can use a mix of antenna to get more range.

    I'm looking forward too seeing result

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    Quote Originally Posted by Pyropetepete View Post
    ...im thinking of 4 to make 360* cover and all to feed one dongle into one Pi.
    I am afraid you will spend quite a lot of work and money earning rubbish. In case, you will involve big dishes - whatever big means - you will get four antennas with an aperture of around 20 degrees each. With 4 times 20 you are far from 360 degrees operation.
    Concerning the feed: In case you would combine the four antenna signals properly you would have a strong 4 times 20 degree reception cover with poor reception in the remaining 280 degrees. In case, you mount 4 antennas, covering around or more than 90 degrees each, you will earn very strange interference effects by multipath reception of the same signal through two antennas, even when cleverly feeding all four singals via an appropriate antenna splitter. Enganging 4 antennas means to build 4 reception chains and multiplex them. e.g. four antennas, four dongles, number of pis under question, ModesMixer2 for multiplexing.

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    Quote Originally Posted by rueckwaertsflieger View Post
    - you will get four antennas with an aperture of around 20 degrees each. With 4 times 20 you are far from 360 degrees operation.
    Concerning the feed: In case you would combine the four antenna signals properly you would have a strong 4 times 20 degree reception cover with poor reception in the remaining 280 degrees. In case, you mount 4 antennas, covering around or more than 90 degrees each, you will earn very strange interference effects by multipath reception of the same signal through two antennas, even when cleverly feeding all four singals via an appropriate antenna splitter. Enganging 4 antennas means to build 4 reception chains and multiplex them. e.g. four antennas, four dongles, number of pis under question, ModesMixer2 for multiplexing.
    You could design a reflector with a 45 degree aperture at 1 GHz in the horizontal and tilt all 4 of them a few degrees (depending on mast height) to catch most of the sky. It would require at least one omni directional to catch the couple of hundred miles of sky directly above and around the receiver.

    You are right that an antenna multiplexer would be the best solution with a single receiver. The multiplexer could be controlled by the pi through the I/O port as a virtual "rotating" directional antenna.

    As I understand Amper's reply above, you can use two DVB-T sticks on one pi? Can you use 4 or 5?
    The problem I see with that is if you have cross over reception from two or more antennas and feeding that to fr24feed from the same account at nearly the same time. But it would solve the multiplexing issues.

    As I understand it, the problem with ADS-B is that the air borne transponders only transmit their position information when interrogated by other radar. So a higher gain receiving antenna won't guarantee a greater range beyond a limit.

    There are ADS-B receivers that actually send out interrogation signals but they are around $1000USD or more and probably require a permit. Their target consumers are private pilots who don't have TCAS and they are not using it with a ground based elaborate high gain antenna array.

    Here is a cute video on youtube from one of the companies:
    https://www.youtube.com/watch?v=JvxvyCVFCVU
    Last edited by Sam26K; 2016-01-21 at 09:18.

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    Quote Originally Posted by Sam26K View Post
    ...You are right that an antenna multiplexer would be the best solution....
    I cannot recommend any antenna multiplexer. Further, I would call that antenna diversity, with a diversity controller choosing the best antenna. In comparison, feeding all four antenna together in an analogue antenna splitter way would cause strange interference effects as said. Again: The "best" way of using four antenna for 360 degrees operation was to use four ANtenna, four dongles, four decoders with n Pis under question, regarding the price point of that components. Everything else sucks. However, even when managing the dishes approach, I do not see any added value, thus no "best" compared to medium gain antenna because reception range with the radiation power of ADS-B transponders is no matter of signal level or antenna gain mainly. It is about line of sight and earth curvature, terrain reflection and absorption, terrain obscuring...
    Quote Originally Posted by Sam26K View Post
    The problem I see with that is if you have cross over reception from two antennas and feeding that to fr24feed from the same account at nearly the same time.
    That is why I recommend ModesMixer2, to my knowledge being a server capable of sorting out dupes.
    Quote Originally Posted by Sam26K View Post
    As I understand it, the problem with ADS-B is that the air borne transponders only transmit their position information when interrogated by other radar. So a higher gain receiving antenna won't guarantee a greater range beyond a limit.
    No. With the B in ADS-B standing for broadcast, position as well as velocity reports are sent out on a regular basis without interrogation from ground.

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    Quote Originally Posted by rueckwaertsflieger View Post
    No. With the B in ADS-B standing for broadcast, position as well as velocity reports are sent out on a regular basis without interrogation from ground.
    That's interesting as I thought that even ADS-B is not broadcast unless it's pinged. I thought that's why all the signals drop off to black and software estimates take over when the planes are a few 100 miles out to sea.

    As far as multiplexing antennas, that's old hat. Switching 1Ghz is not that hard. I would build it from scratch rather than trying to buy one off the shelf though. You can do it with mosfets configured as analog switches with surface mount components, microwave pcb and RF enclosure and connectors. You could switch the mosfets (and antennas) from the pi's I/O lines

    Of course that approach does require some basic understanding of designing with 1GHz and isolating the antenna paths so they don't interfere with each other inside the multiplexer. The best designs actually use a sandwich approach with two microwave pcb's with the surface mount components in the center and the outside of the pcb's are completely shielded by the unetched copper clad outer layer. The sandwich design utilizes characteristics that are better transmission lines to match impedance and minimize loss with high isolation between antenna ports.
    Last edited by Sam26K; 2016-01-21 at 10:43.

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