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Oct 08, 2013, 03:04 AM

FrSky Rx Antenna Placement Questions

Hi, I've got some noob antenna questions, hoping someone can please give me a hand...

- I'm trying to build up my Bilxer 1 up for FPV & range. I've got an FrSky D8R-II Plus receiver, with the two dipole antennae. I'd like to have a better understanding of how receiver & antennae layout will affect the FrSky's performance. So, I've got the following questions:

1) The actual antenna is the small, 33mm white 'tip' at the end of the cable, and the rest is just a coax extension (i.e., has nothing to do with the antenna's gain or performance), correct or incorrect?

2) the optimum layout is for each 'dipole tip' (the white part) to be @ 90 degrees from the other, correct or incorrect?

3) assuming that #2 is true, should the 'right angle' formed by the dipoles be in a vertical 'V' configuration, or should it be in an 'L' configuration (i.e., offset 45 degrees from the ground/horizontal plane, or perpendicular to the horizontal plane) ???

4) again, assuming that #2 is true, does the 'distance' of each dipole tip from the 'origin' of the two have any effect on the combined dipole antenna's performance? (i.e., does increasing the distance between each tip improve or degrade performance, or is it irrelevant?)

And, does each dipole tip need to be equidistant from the origin, or is it irrelevant?
Example: For an L configuration of the dipoles along the plane's vertical & horizontal stabilizers, and assuming a layout where the vertical dipole goes up 15cm while the horizontal dipole goes out 20cm, would it matter that the vertical & horizontal distances are not equal?

5) Apparently, my plane's EPO foam should be 'invisible' to the 2.4GHz microwaves for the RC link, correct or incorrect? If correct, then why does my RSSI sometimes change dramatically with large changes in the plane's orientation? (i.e., I can get a big drop off with bad orientation, where there's nothing between me & the antennae other than the plane's foam body)

6) Not really a question, need advice on the following:
I just got a pair of 'FrSky 40cm extension' dipole antennae from HobbyKing, and I'm trying to figure out how to best mount them. A popular setup seems to be placing them along the horizontal & vertical stabilizers, which basically means that I'd have to find a way to mount the Rx closer to the tail... I've got this 'mock-up' so far...
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I'm not sure if that's an optimal setup or if it should be changed.
Any feedback or advice would be greatly appreciated...

Also, can someone please explain what that bulky part with black heat-shrink on the FrSky extension antenna is?

Up until now, I've had the receiver up front, and have just been poking the antennae out from the sides of the 'cockpit' cover (in either an 'L' config, one vertically/one horizontally, or a 'V' config, each tip out 45 degrees). It might just be coincidence, but I've noticed that setting up the antennae in a 'V' instead of an 'L' seems to give me a more stable RSSI value & little more distance before I start hearing any 'beeps' from the Tx (though I might be wrong about this, and perhaps it has nothing to do with my antenna configuration).

Anyway, any info/feedback on this stuff would be a huge help, thanks!
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Oct 08, 2013, 06:44 AM
Registered User
1 - correct

2 - correct, the reason being that it covers most flight orientations align well with tx antenna so bear in mind you might fly fpv in less aerobatic style so generally one fore-to-aft and the other left-to-right and not necessarily vertical. BUT there is another train of thought that suggest your tx ant should be more vertical in which case your rx ant's would be better in a vertical orientation.

3 - Either really, What you are trying to do is keep the tx and rx antennas aligned for as many flight orienatations as you can.

4 - Further part could be better since it will provide more coverage if one is blocked by motor, battery etc

5 - I'm not sure foam is truly 100% transparent, other things can also block the signal but also if the movement causes the tx and rx ants to move out of matching alignment then your rssi will drop

6 - If your tx ant is vertical then the horizontal antenna is only really used when the plane rolls so it is aligned with the tx. If your tx ant is horizontal, then the one on the vert stab is only used when the plane rolls for the same reason.

The extended antenna leads are a 'sleeved dipole' design which improves their sensitivity ie range.

To summarise, the aim is to position your rx antennas so they remain aligned with your tx antenna in as many plane orientations that you are likely to fly.

Hope that helps

Oct 17, 2013, 10:48 AM
Registered User

i stumbled on this thread while looking for info on your kk project and while hangaspace already gave you a lot of good answers to a lot of good questions, i wanted to mention my experience with a very similar setup:

ive been fpv flying a skysurfer (==bixler1) paired with a 4chan frsky receiver for a well over a year - hundreds flights. lots of experimenting with antennas & placements have gotten me from triple beeps @ 2km to almost no beeps at 7km - battery & video has stopped me from going further. my current setup is basically identical to your pictures: the balun antennas (identified by black shrinkwrap on top of it) works miracles, as does mounting them just like you have on the horizontal/vertical stabilizers. the third part is using a high gain antenna on the tx (DIY biquad in my case). others have gone twice the range with a similar setup.

also: "ive noticed that setting up the antennae in a 'V' instead of an 'L' seems to give me a more stable RSSI value". it is always dangerous to speculate about RF as theory and reality does not always line up , but as hangarspace mentions, assuming that you hold your tx antenna vertical, your current setup will result in perfect conditions for vertical rx antenna and worst case for horizontal one while maintaining level flight. only in a hard bank or dive will horizontal antenna experience better conditions. not the type of flying most of us do at extended distances. a v-configuration will result in so-so conditions for both antennas during level flight and only ideal conditions for one of them during a bank. thus, for docile long range i believe your current setup is better, about the only disadvantage i can think of is that if your vertiical antenna somrehow pops loose while far out, your horizontal may not be able to save your bacon so you better have that RTH built by then

edit: lots of good info for you in this thread:

you can see my setup in post #230 (looks familiar doesnt it?). ive gone to 7.5km with the same setup since i did that post
Last edited by fpvwannabe; Oct 17, 2013 at 10:52 AM. Reason: adding link
Jan 15, 2016, 05:19 AM
Registered User
Hi, I am using a FrSky D8R-II PLUS 2.4Ghz 8CH Receiver with Telemetery and i lost one of the two antenna, is it going to effect the performance of my reciever? will I not be able to use it at all?
Last edited by hanns; Jan 20, 2016 at 09:00 PM.

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