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Range extender... 2 Antenna question

Discussion in 'Phantom 2 Vision + Mods' started by justin00, Oct 16, 2014.

  1. justin00

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    Hey folks

    So upon my investigations logging into the range extender via SSH.. It appears that....
    a) The range extender is a client to the Phantoms access point to get the tele data/FPV
    b) The range extender also acts as a access point for your phone/device to connect to...
    it then bridges the 2 WIFI connections so the Range extender, Phone/device and Phantom are all on the same IP network/subnet.

    I see everybody upgrades both antenna's in the RE... Sooo my question is... Do you really need to upgrade the antenna that is used for connectivity to the phone/device ??

    I am assuming each antenna is used for each thing I listed above....

    What peoples thoughts... ? Am I completely way off ?
     
  2. allemtura

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    Hi Justin,

    The antennas used in the range extender are for both the phone and video feed to the Phantom, so whilst the upgrade makes no difference with the phone connection, it definitely does make a difference with the Phantom connection. Unless I've misunderstood your question?
     
  3. justin00

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    Ok thanks.

    I just assumed 1 antenna was for the Phantoms connection and another is for the phones connection.

    I cant remember if when you login to RE you see wlan0 and wlan1.. Probably not based on your answer. Pretty clever if they have used the same wifi adaptor to be associated with 2 diff SSID's (1 as client and other as A.P)

    You've understood heh :) Thanks
     
  4. justin00

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    Hmmmm I am tempted to open the RE and disconnect one of the antenna cables... Just want to double check..
    It seems extremely odd that both antenna's are used to connect to the Phantom (as a client) and also use same 2 antennas to act as an access point (for phones to connect to).
    It does seem like there is only 1 wifi module, but who knows how it works/whats in it..

    You guys see my confusion/why I think its odd ??
     
  5. Loaderbull

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    Both antenna's face the Phantom, i'm sure it just works as a diversity reciever, however i do hear what you're saying regarding how the phone then connects to the RE..The antenna's are just 1" square panel antenna's. Anyone actually know how the RE connects to the phone in respect to antenna etc? If one was a phone antenna then i'm guessing they wouldn't point it in the same direction (forward) as the Phantom one, as the phone will always be behind the RE?
     
  6. kondorfpv

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    It's actually quite impossible that 1 antenna would be used to connect to the phone and the other one to the phantom itself, being the phone less than a foot away from the extender, it's an access point- repeater , good for a multipoint connection, not a bridge. Not only does it work as a diversity setup, but also takes advantage of MIMO technology, combining the data streams received by both transceivers/antennas.
    Tony.
     
  7. justin00

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    perhaps It's a terminology issue.
    When we use Wifi repeaters at work (for fibre, Wifi or any transmission medium) it kind of acts as an amplifier (well in some setups) It takes existing signal and outputs it at a stronger power.. Or for the cheaper devices which are purely repeaters and don't do any amplification, they sit in the middle and repeat the signal to increase the range of the signal, in respects to Wifi.

    The RE has 2 different SSIDs that make up the 1 repeater.
    FC200_XXXXX for the phantom
    Phantom_XXXX for the device.

    To me it doesn't exactly sound like a repeater.. in the sense of the word. I'm just having problems getting what I am trying to say out clearly.. but either or.. it really doesn't matter. You guys have answered the questions in regards to the 2 antenna's so all good :)

    Thanks
     
  8. Foosy

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    One antenna can broadcast multiple SSIDs, or multiple networks. It is the same concept as a radio antenna that can receive multiple stations.
    Most access points today allow you to define multiple network segments, each using a different SSID, and a different encryption.
    Using two antennas allows using signal diversity to improve the quality and reliability of the received signals. There are a few ways the receiver can use these two signals, achieving different results based on the complexity of the receiver design:
    (as per wikipedia)
    - Switching – In a switching receiver, the signal from only one antenna is fed to the receiver for as long as the quality of that signal remains above some prescribed threshold. If and when the signal degrades, another antenna is switched in. Switching is the easiest and least power consuming of the antenna diversity processing techniques but periods of fading and desynchronization may occur while the quality of one antenna degrades and another antenna link is established.

    - Selecting – As with switching, selection processing presents only one antenna’s signal to the receiver at any given time. The antenna chosen, however, is based on the best signal-to-noise ratio (SNR) among the received signals. This requires that a pre-measurement take place and that all antennas have established connections (at least during the SNR measurement) leading to a higher power requirement. The actual selection process can take place in between received packets of information. This ensures that a single antenna connection is maintained as much as possible. Switching can then take place on a packet-by-packet basis if necessary.

    - Combining – In combining, all antennas maintain established connections at all times. The signals are then combined and presented to the receiver. Depending on the sophistication of the system, the signals can be added directly (equal gain combining) or weighted and added coherently (maximal-ratio combining). Such a system provides the greatest resistance to fading but since all the receive paths must remain energized, it also consumes the most power.

    - Dynamic Control – Dynamically controlled receivers are capable of choosing from the above processing schemes for whenever the situation arises. While much more complex, they optimize the power vs. performance trade-off. Transitions between modes and/or antenna connections are signaled by a change in the perceived quality of the link. In situations of low fading, the receiver can employ no diversity and use the signal presented by a single antenna. As conditions degrade, the receiver can then assume the more highly reliable but power-hungry modes described above.


    Not sure which way dji implemented the range extender. Regardless, it is not a repeater as you correctly observed, because they are using two different SSIDs.
    If they had used it as a true repeater you would have been able to connect to the phantom directly. Further we can learn that the other SSID must be hidden because it does not show up on your device as an option to connect to.
    I wonder if this "signal hand-over" is not causing unnecessary delay in the video transmission...
     
  9. justin00

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    Yeah the FC200_XXXXXX is hidden, This can be verified (obviously its not in the list as you said) if you SSH into the Phanton and look in /etc/config/wireless... In the FC200_XXXX SSID part of config it has the line "hidden 1" - setting to 1 hides the SSID..

    If you SSH into the RE and look in /etc/config/wireless under the Phantom_XXXXX SSID config it has "hidden 0" which is opposite.

    Alternatively if you have a wifi analyzer app for Android or use Linux, both of these have the ability to see hidden SSID even if not connected, so the FC200_XXXX SSID can easily be seen.

    You raise a good point about 1 Wifi adaptor being able to do things to multiple SSID...I completely forgot about this lol... Heck my home wireless router (Cisco 877W) can even do this... So thanks for bringing that up, and also the other info you got from wikipedia :)

    What do you mean by delay in video transmissions ?? What delay are you getting ? The RE seems to just combine (I'd call it a bridge) the FC200 and Phantom_XX SSID's which puts the Phantom, RE and phone in the same 192.168.1.x/24 networkt

    Anyways the multiple SSID being run off same adaptor was throwing my thinking off the most, so thanks for that. I get how its all working now, finally =) Well actually the only part I don't get is how the RE is only turning on its AP (to allow you to connect to Phantom_XXXX) once it is connected the FC200_XXX... It is probably a setting in /etc/config/wireless but I am not going to look into it any further, It really doesn't make a difference how that part is working and you folks have answered my main question/purpose of starting thread...so thanks again all!!