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MX-20 range and antenna position

Discussion in 'Electronics' started by Scott Aubuchon, May 13, 2013.

  1. Scott Aubuchon

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    Been having issues with my receiver strength... was just shooting a golf course the other day and was 170 yards away and totally lost communication. Thankfully I was low and slow so no real damage... BUT, wth! I'm glad I wasn't over water or real high.

    I'm trying to figure out why I totally lost communication. The only thing I can think was that I hit my antenna all the way to one side (for whatever reason). I was line of sight, only one small (non-leafed out) tree in-between.

    Just has me really concerned moving (or flying) forward. :/
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Scott: can you share details of the transmitter/receiver and perhaps post an image of how you have the transmitter (EDIT by Andy) Receiver! installed on the copter?

    Andy.
     
  3. Steve Maller

    Steve Maller UAV Grief Counselor

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    And if you are a Mikrokopter guy and have a GPX file from your Navi board, that'd be super helpful, too.
     
  4. Gary Haynes

    Gary Haynes Administrator
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    Scott watching some of Holger's videos I have seen him have the antenna pointing up on the TX and horizontal on the TX. I've flown both ways and frankly can't really tell a difference. The techies will weigh in but more likely most of the time the position of the receiver antenna is more important. As requested post a photo of the copter install. If you are using the Graupner system and have turned on logging in the Graupner you can pull the data file and it will tell you very accurately what happend on the TX/RX strength.
     
  5. Steve Maller

    Steve Maller UAV Grief Counselor

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    Scott, you said "Been having issues with my receiver strength". What kind of issues, and how do you know that was the issue?
    Again, a GPX file (or a few) can help us all understand what's going on.
     
  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    For whip antennae (of the form we typically find on RC transmitters), if the antenna is vertical most of the energy is emitted in a doughnut shape, horizontally parallel to the surface of the earth:

    The whip antenna can be considered half of a dipole antenna, and like a vertical dipole has an omnidirectional radiation pattern, radiating equal radio power in all azimuthal directions (perpendicular to the antenna's axis), with the radiated power falling off with elevation angle to zero on the antenna's axis. Whip antennas 1/4 wavelength long or less (the most common type) have a single main lobe, with field strength maximum in horizontal directions, falling monotonically to zero on the axis. Antennas longer than a quarter wavelength have patterns consisting of several conical "lobes"; with radiation maxima at several elevation angles; the longer the electrical length of the antenna, the more lobes the pattern has.​

    Vertical whip antennas are widely used for nondirectional radio communication on the surface of the Earth, where the direction to the transmitter (or the receiver) is unknown or constantly changing, for example in portable FM radio receivers, walkie-talkies, and two-way radios in vehicles. This is because they transmit (or receive) equally well in all horizontal directions, while radiating little radio energy up into the sky where it is wasted.​


    Thus, if you have a whip antenna horizontal, then most of the energy is radiated outwards at 90 degrees to the axis of the antenna -- so lots of energy goes straight up, lots of energy goes straight down -- but some of it does go horizontally -- but at 90 degrees to the direction towards which the antenna is pointing.

    Therefore, what Holger may do will work for short range, but for longer range have both the Tx and Rx antennae vertical -- then most of the Tx's energy is radiating outwards horizontally from where you are standing. If you want maximum range, tip the Tx antenna tip back towards you so that the RF power "doughnut" tips down towards you and up towards to the copter.

    Does it make a huge difference? I don't know. You'd have to measure it. But it certainly doesn't help to have the Tx and Rx antenna (a) horizontal (remember for Graupner it is also transmitting telemetry back to the ground), and (b) and the Rx antenna strapped to carbon fiber (which absorbs radio frequency signals -- do a Google search for "does carbon fiber absorb RF" (without the quotation marks and see! :) )

    Check out the Modi-fly Rabbit at http://www.quadrocopter.com/Modi-Fly-Receiver-Rabbit_p_668.html -- that holds the antennae (a) at 45 degrees to each other -- which looks like a vertical antenna, in effect.

    By the way, if I understand the design correctly, the Bluebeam antennae also need to be oriented up or done -- the peculiar lobe shape of the antennae imparts a spin (a.k.a. polarization) to the outgoing radio frequency waves -- which the lobe shape of the receiver is optimized to pick up.

    If we have any EE/Antenna design gurus on the forum, please correct me if I'm wrong. Antenna design seems to be a cross between an art and a science.

    Andy.
     
  7. Scott Aubuchon

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    Well, I usually listen to voltage and receiver strength while flying and have noticed that the receiver strength will bounce all over... sometimes she reports 0% right after 95%... its strange.

    I will post the files once I get back to my home office later tonight. Thanks
     
  8. Scott Aubuchon

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    I will post pics later tonight, thanks
     
  9. Steve Maller

    Steve Maller UAV Grief Counselor

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    I get the same thing with voltage level from the Fraulein every so often whilst airborne. It always gives me a start when she declares, "Voltage level 0.0 volts". :eek:

    Not sure why the telemetry channel is prone to dropouts, but I have never seen that reflected in my GPX files (which I review religiously), so it must be the downlink. That's why I asked you to see a GPX file: I don't fully trust the downlink channel.
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Yeah. I've had that too -- pretty regularly, and your brain gets pulled back to focus on her voice with a "What did she just say?" moment.....

    Andy.
     
  11. Scott Aubuchon

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    sorry for the delay guys, work sometimes always gets in the way. Having never really looked at my log files (yes, I did just say that). Is there a way to transfer from the SD card via MK tools? I don't have a microsd card reader handy.

    I tried to use the MK_GPX tool and used the import from MK tool feature, but it didn't work and I had little time to look at it. I am for sure going to dedicate some time tonight on it.
     
  12. Steve Maller

    Steve Maller UAV Grief Counselor

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    Most microSD cards come with a 'cradle' for turning your microSD card into a regular SD card. Do you have one of those? If not, you're SOOL. You could upgrade to the latest MK firmwares and software, and I think they allow you to pull the logs from the copter without removing the microSD card. But that's a big leap.
     
  13. Gary Haynes

    Gary Haynes Administrator
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    Scott the latest update from MK has the ability to download directly from the NAVI board. All of the instructions to get to .90 version of FC and NAVI are on the MK Wiki.
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Gary: As I recall, the latest firmware (which uses a simple FTP server on the Navi Board) only allows for retrieving a single GPX file at a time doesn't it? It's a useful start, but would be quite tedious if you have lots of files.

    Andy.
     
  15. Gary Haynes

    Gary Haynes Administrator
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  16. Scott Aubuchon

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    So, I found my SD card holder and loaded up the card.... k, so this was my first time viewing the log files. Great info, don't ask why I never looked before. :) Anyway, I had a ton of log files, but none past 12.17.2012... strange... I wonder what happened after that day? So, for the original question, I guess we will never know.

    But in general, how do you point your antenna on the MX-20? I usually have it straight out, but that day noticed it was turned... and that was just a thought. But willing to guess it could have been any number of issues.

    Also, since I am doing all this discovery, I am upgrading to the latest firmware on navi and flt controller. Anybody want to yell "STOP!", or should we be good. And does upgrading wipe away or reset any of my custom settings? I have them backed up and I have a screen shot of the settings as well (pretty stock anyway)... but just curious. Probably best to revisit those settings anyway.

    Sorry for the thread scope creep :O

    Thanks guys
     
  17. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Scott:
    Not sure why logging would have stopped at 12.17.2012. I'd copy the files on the microSD card to the hard disk of your laptop and reformat the card. But NOTE: If you have commercial GPS license there's a file that needs to be on the card. All other files, eg. SETTINGS.INI will be recreated. Also note, you will not get a log file (with the new firmware) unless you have a GPS date (it used to be a GPS fix but that changed) -- the date is used to create the file name -- and you increase the throttle above 40% (which, if you have the props on, means you're flying). The logging continues for two or three seconds after motor stop -- so don't be too quick to unplug the LIPO otherwise you will lose a chunk of the GPX file.

    Point the MX-20 antenna straight up -- the RF energy radiates sideway in a disk around the tip of the antenna. You'll get much better range.
    Make sure that the antennae on the Receiver are not in close proximity to RF-absorbing carbon fiber...you might want to consider getting the Modi-Fly RX holder. http://www.quadrocopter.com/Modi-Fly-Receiver-Rabbit_p_668.html that holds the Rx and its antennae up high.

    I would always presume that you need to set the MK Tool settings after an upgrade. It may not clobber them, but "distrust and verify."

    I've not heard bad things about the latest firmware -- other than I think with voice response where it tells Gary and Dave "UP" when their bird first takes off. Personally, I think that's probably very sound advice..... ;)

    Hope this helps.

    Andy.
     
  18. Scott Aubuchon

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    Updated everything, and MK is now writing a log again. I have attached a GPX, anything look out of place? Also, I attached a screen shot of all my configuration. Anything advise on settings would be greatly appreciated? See File

    Thanks!
     

    Attached Files:

  19. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    GPX file looks nominal. House looks great! :)
    If you want to make sure you always get a GPX file, then on the MISC window, you might want to check the SD Card Missing and GPX fix missing checkboxes.

    Hope that helps
    Andy.
     
  20. Scott Aubuchon

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