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Thread: RSSI from Spektrum receivers

  1. #1
    Join Date
    Apr 2012

    RSSI from Spektrum receivers

    It is working

    So far only bench tests with AR7000 DSM2. Upper right corner shows how RSSI reacts while switching on and off the DX8 TX.

  2. #2
    Join Date
    Jun 2012

    This is the link for the people that want to buy it.

    Is it possible for you to make a testflight video? So that we can watch the RSSI in flight?

  3. #3
    Join Date
    Jun 2011
    Durango, CO
    I have an ar7000 DSM2 Rx laying around. You are using this with no modifications using this DORA board?

  4. #4
    Join Date
    Apr 2012
    The installation of DORA is as simple as it can be. No mod. It takes 5 min. - you need to connect it to a RX data output port and then the other end to analog RSSI input of your OSD. Calibrate the OSD RSSI readings (in my case TX on and then TX off) and that is it.

    So I have done two tests today.

    1. Typical in-flight situation. Quadrocopter, standard Spektrum TX/RX (DSM2, AR7000+sat and DX8) with standard antennas. Ca. 1300m (0.8 miles) from the ground base. Basically no signal loss except few drops around maximum distance achieved. Other than that perfect signal during the entire flight. Please bear in mind that I have EU TX, so it has 70mW module (+ antenna gain).

    The clip is extremely boring and takes about 5 min.

    2. Non-flight test. I left my quad on the balcony of my house next the my ground station and took the TX for a walk It was not that far in terms of a distance (ca. 350m/ 0.2 miles max) but there were quite a few houses in between TX-RX. In the clip you can see there were some drops in RSSI (in the end I have switch off the TX for a few moments).

    Short version with cut scenes when nothing was happening:

    And the full 10 min one for those that have too much time :

    As expected (because of digital transmission characteristic) the drop is very sudden (as well as recovery) - please remember that I was only walking, so my speed was pretty low. In other words you have to be very careful while relaying on RSSI status during normal flight. I believe this is the reason that the manual says that RSSI value below 80% (on the scale from 0 to 100, were 100 represents best signal) should cause your immediate reaction resulting in finding position with better signal.

  5. #5
    RTFM aeryck's Avatar
    Join Date
    Aug 2011
    SE Michigan
    I'm curious to know how this thing interprets Spektrum's flight log data. As we all know, Spektrum does not give a true RSSI reading - Rather, it reports information on antenna fades, lost packets, and holds (which happen after X consecutive lost packets). Near as I can tell, the best guess this thing can tell you is that either you have a signal or you don't.
    Far better is it to dare mighty things, even though checkered by failure; than to take rank with those who neither enjoy much or suffer much, because they live in the gray twilight that knows not victory nor defeat.

  6. #6
    Join Date
    Apr 2012
    That is correct. This is not a real RSSI. It rather calculates signal loss and represents it as "RSSI" voltage. Based on the product description it is not just 0-1 detection. And based on my short experience with it I can only confirm this. There is some logic that stands behind the calculations depending on the signal loss intensity. Would be good if the designer could comment on this...

  7. #7

    Designer's note

    Hi there,

    It is correct that what DORA gets from the receiver are 3 groups of digital information (“Antenna Fades”, “Frame Losses” and “Holds”).

    So with a single system receiver everything happens rather abruptly: you get antenna fades then frame losses and then the model goes into hold mode.

    My first Youtube flight video with DORA was made with such configuration (AR600 DX6i) and one can see that the RSSI transitions quickly from full signal to zero.

    It still is a big help though because without the RSSI input you often miss brief holds until you arrive at a distance where the connection is permanently lost. With DORA you just wait for the connection to come back and turn the craft towards home..

    With a multisystem receiver the antenna fades set in much earlier as usually one system is in a less than perfect orientation. This gives a warning time long enough to avoid going into hold conditions.

    The constant channel hopping of DSMX adds to this effect. Now every receiver subsystem will see fades from time to time so as DORA averages over time and systems you get an even more gradual behavior.

    I have upgraded first to a AR7010 and recently to a DX7s and I’m quite happy with the result.

    Another feature of the algorithm is the “limiting” of the different transmission incidents which allows distinguishing what is going on.
    So the antenna fades are limited to take off up to 20% of the RSSI. So as long as the RSSI is above 80% all you see is fades (which means no complete telegram is lost).

    The frame losses take off 60%. Since they will be always accompanied by lots of antenna fades the RSSI now goes down to 20%..30%.

    A Hold brings the RSSI to zero, since that is as bad as it gets.

    This sounds a bit confusing but after flying with Dora a bit it becomes quite natural to understand what the value is saying and also when it is time to turn around..

    Hope this helps.

  8. #8
    Join Date
    Apr 2012
    Hi Frank, good to see you on FPVLAB

  9. #9
    Navigator hockeymonkeymark's Avatar
    Join Date
    Apr 2012
    Arlington, Texas
    I just installed this on my quad and had a few questions. The digital spectrum signal is sent through DORA and is still a digital signal on the other side correct? It hasn't been converted to an analog value or signal correct? and I guess the I need to turn the pentometer to best find that sweetspot voltage before I drop out..?

  10. #10
    Join Date
    Apr 2012
    The outcome of DORA is a normal analog signal (the voltage that is changing). The only thing I have done with my unit was a RSSI calibration in my OSD (I have not calibrated DORA as such). In my OSD the calibration is as easy as it can be. You switch on the RC and calibrate OSD at "max" RC RSSI. Then you switch off the RC TX and calibrate OSD at no signal. In the background the OSD calculates and remember best signal voltage and worst signal voltage and then represent it in signal % (highest/best as 100% and worse signal as 0%).

    So, I'd say you need to look into your OSD manual, rather then DORA.

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