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Thread: 2.4 Ghz and Water

  1. #1

    Default 2.4 Ghz and Water

    There has been some chatter on various boards as to the suitability of 2.4 Ghz equipment for R/C boats, including anecdotal evidence that a) some Spektrum employees discouraged people from using their gear on boats and b) plenty of people ignored the advice and things seem to work just fine. Googling around located a fair amount of theoretical information on absorption of microwaves by water but not much experimental evidence. So I decided to run some simple tests.

    The test rig is shown in the photo: a waterproof Otterbox with a clear cover, some AAA batteries, a Futaba R616FFM receiver, and a fishing sinker. The receiver is Futaba's "park flyer" offering with less range than their main 2.4 Ghz products. It is attractive to RG65 and Footy sailors owing to its small size, and is also cheaper. It has a short stub antenna instead of the "twin lead" one on the larger receivers. Like all the Futaba receivers it has an LED which glows green when the receiver is linked to the transmitter and red when it is not. The transmitter used in the test was the T6EX.

    For the tests, the transmitter and receiver were powered up, the box closed and the rig dunked while observing the LED. The transmitter was placed on a chair about 2 feet above the surface of the water.

    The first test was close range submergence about 6 feet from the transmitter. The link was consistently broken when the receiver antenna was 1/2 to 3/4 inch below the water.

    The second test was a range test about 250 feet from the transmitter. Link was maintained with the antenna just at the water line and consistently broken with slight (1/4 inch or so) submergence.

    The lesson is the obvious one of keeping the antenna above the water line. In the case of the R616FFM it would probably be wise to have the antenna stick up through the deck.

    The test was conducted under calm conditions and did not assess the possible effect of microwave reflection off of waves. Since 2.4 Ghz is the frequency at which microwave ovens operate, I doubt that this is much of a factor. On the other hand, when sailing in truly desperate conditions, it is possible that a low-lying antenna could be in the "shadow" of a wave and break link. And of course, the "full size" receivers are almost certainly better in all circumstances.

    Cheers,

    Earl
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  2. #2
    Join Date
    May 2007
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    Mahwah, NJ USA
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    Thumbs up Re: 2.4 Ghz and Water

    An excellent test! Thank you for sharing the data.
    Footy #95 - Pepsi Torpedo (returned to township re-cycling bin)
    Footy #140 - 3-Liter Torpedo (root beer bottle) - still competitive, partially retired
    Footy #340 - Modified Bob-About 2 - actively competing
    Footy #395 - Keel-Forward Footy with 14" water line

  3. #3
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    Apr 2008
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    South Florida, USA
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    Default Re: 2.4 Ghz and Water

    Hi Earl,

    Thanks for posting this info. I have just received on of the new Spektrum 5 channel sets, and I've noticed that the included AR500 5 channel Full Range receiver has two antennas, one that is about an inch long, and the other is about 9 inches. I guess I'll be running the 9 inch lead out the hull and up vertically using an inner length of "nyrod" pushrod material like I have done with my 27 & 75mhz receivers. Hopefully, that will be higher than any waves (if not, I probably shouldn't consider sailing in those conditions anyway!).

    Regards,
    Bill Nielsen
    Oakland Park, FL USA

  4. #4
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    Jul 2005
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    Brooklyn, NY USA
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    Default Re: 2.4 Ghz and Water

    Hi Guys, On my recent vacation I had an opportunity to sail Brujo in the same rough conditions that were shown in my Bantam pics, 6 to 8 mph winds with gusts over 10. There were pretty big waves and some whitecaps. My Spectrum 6 radio had no problems.
    On Brujo the receiver is mounted under the deck. I was sailing from an adirondack chair on my dock which is a lower vantage point than standing and walking which is how I race. I am not sure that this is an issue.

  5. #5

    Default Re: 2.4 Ghz and Water

    Somebody needs to be the bad guy and determine if it really was a real great test.

    Earl,

    Was the receiver/box covered with water or was it sitting in a hole in the water? A boat hull would be a hole in the water. Seems like a big difference. This is not entirely clear to me from your description of the test, although I would almost bet money that the box was submerged and it was not a valid test.
    Scott

  6. #6

    Default Re: 2.4 Ghz and Water

    It was submerged to check worst case. Your point is valid for hulls in that some signal may propagate through deck and air space, although since microwaves are line of sight I don't think there's much help for antennae under the water line. I was just interested in how much "thickness" of water it took to break link. Somebody else can test simulated hulls (my receiver is back in the boat :-))

    Cheers,

    Earl

  7. #7
    Join Date
    Jan 2006
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    Canada
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    Default Re: 2.4 Ghz and Water

    2.4gig has now been in use for several years in the IOM racing fleet with no reported problems due to water affecting signals.

    In my IOM, my Rx is velcroed under the deck. One ariel runs lengthways and the other runs across the beam (to give the 90 degree as required). I have had no issues of any kind. Works great. If the boat is healed, then at least one ariel will be above the water.
    John Ball
    CRYA #895
    IOM CAN 307 V8

  8. #8

    Default Re: 2.4 Ghz and Water

    Quote Originally Posted by hiljoball View Post
    2.4gig has now been in use for several years in the IOM racing fleet with no reported problems due to water affecting signals.
    Yes, there's plenty of evidence that the larger receivers work fine in larger boats. I was interested in the much smaller and shorter-range "park flyer" receiver in worst case (submerged) conditions.

    Cheers,

    Earl

  9. #9
    Join Date
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    Summers - Lake Fenton, MI Winters: Sebring, FL
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    Default Binding Delay

    Has anyone ever noticed a delay when doing initial binding?

    It seems that it may be related to CDMA cell phone iin pocket, but not sure.

    Also occasional delay when turning system on.
    Best Regards, Frank

    US-12
    Soling 1M
    Fairwind
    ASymetrical Stern Footys
    FF-1 007 "Half @$$" w/Flames
    FF-2 007 "GoldFoot" w/Direct Drive Rudder

  10. #10
    Join Date
    Apr 2008
    Location
    South Florida, USA
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    Default Re: Binding Delay

    Quote Originally Posted by ffastffrank View Post
    Has anyone ever noticed a delay when doing initial binding?

    It seems that it may be related to CDMA cell phone iin pocket, but not sure.

    Also occasional delay when turning system on.

    Hi Frank,
    i can't remember exactly where I saw it, probably on the Spektrum site's FAQ section or maybe somewhere in the instructions, but Spektrum mentioned this problem can be due to several things, including interference, or even just having the Tx too close to the Rx (they recommend at least 4' between the two).
    Regards,
    Bill Nielsen
    Oakland Park, FL USA

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