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Question About Parabolic Antenna Attachments and "SWR"

Discussion in 'Pro/Adv Discussion' started by Bigfootbuilt, May 30, 2016.

  1. Bigfootbuilt

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    I've watched several videos and read articles about various parabolic attachments for the DJI transmitters but it got me to thinking about what effect this would have on the transmitter itself. If any of you are old enough to remember the CB radio days, care was taken to lower, as much as possible, the SWR (Standing Wave Ratio) of the transmitter. The higher the number, the more of the signal was being reflected back to the transmitter causing it to overheat and burn it up eventually. My question is, does the same apply to RC transmitters? Does anyone know? Would using parabolic attachments like the Skyreat copper reflectors shorten the life of the RC since half the signal is being reflected right back to the transmitter?
     
  2. Pheonix7

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    I'm a ham operator and I wouldn't think this would be the case as the rf has already been transmitted via the antenna. I see the windsurfers as just a reflector of transmitted rf. SWR mainly comes into play if an antenna isn't properly tuned for a specific frequency which restricts the transmitters ability to emit rf appropriately via the antenna resulting in energy return to the transmitter itself.


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  3. Bigfootbuilt

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    But isn't reflection coefficient taken into account when measuring SWR? I remember being able to adjust radio antennas to lower the SWR but it had to be in an open area, because as soon as you get near a metal building or another vehicle, the SWR would rise again.
     
  4. WetDog

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    Yes, SWR is important. For a reflector like a Windsurfer it's likely not going to change much (yes, SWR changes with near field but if the Windsurfer is properly designed it should be OK). Hopefully the commercial antennas like the FPVLR and ITELITE flavors have had their base SWR checked.

    Unfortunately, it's pretty hard for all but dedicated microwave enthusiasts to determine SWR for a given antenna system. They do make commercial SWR meters for than range but they tend to be expensive. They're actually pretty easy to make if you have any electronics background (look them up). Might be a fun project.
     
  5. Pheonix7

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    This. Yes it's taken into account but at the low rf levels the remote is producing I can't see how it would be an issue.



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  6. WetDog

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    You certainly would not get heating and you are probably not at much risk of transmitter damage but you would lose efficiency which could be important especially given the low output.
     
  7. Bigfootbuilt

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    Thanks for the replies guys. Around here it is difficult to get distance because of dense trees (I live in South Carolina) and I was looking at the Skyreat parabolic attachments in particular, but either way, I think as long as obstacles like trees are between me and the P3A, it probably won't make much difference in most places no matter what mods I have on the RC. It would still be nice to have if I had a clear line of sight and a distant target to fly to.
     
  8. WetDog

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    Yeah, trees are a *****. They're just water and 2.4 Ghz signals love to interact with water. What we need is a skyhook system. A small UAV with a pair of narrow angle antennas - one pointed down and one horizontal. A radio set up as a 'bent pipe repeater' which takes the signals from one antenna and stuffs them out the other. Lots of battery and GPS so it will hover in place. Then rig it to talk to the Phantom and the RC.

    Probably take a set of competent engineers about a year to put it together and the FAA (and FCC for that matter) about an hour to shut it down.

    Tall ladders might be an option.