Receiver antennas placement in your copters

[LordPikaChu]

Hello everyone!

I was wondering how other people mount their receivers on their machines and what's their reasoning behind mounting them in a particular way.

I have recently stumbled upon , which is a simple 'rabbit' to keep antennas on Graupner receivers at right angle. What bugs me (and that's why I've created this thread) is that on second photo on the linked page they propose mounting the receiver so that one antenna stands vertically and the second one is positioned horizontally. In addition to that, they keep the receiver at the top of the copter.

Why should the receiver be mounted this way? Wouldn't it be better to keep the receiver at the bottom of the frame so that the frame itself doesn't get in the way of radio signal? Most of the time the copter will be above pilot's head so if the Rx is mounted as Quadrocopter.com suggests, it would be hidden behind copter frame most of the time (from pilot's perspective).

Now, horizontal/vertical positioning of separate antennas - shouldn't the receiver antennas be both positioned horizontally, but one, for example, pointing back and the second one pointing right? I always thought that the signal coming from Tx is polarized the way that your Tx antenna is kept, so, if I keep my Tx antenna pointing right, this would create horizontally polarized signal. Why would I then want to mount one of my antennas vertically, as Quadrocopter.com suggests? Multicopter platforms usually fly leveled (not talking about acrobatics), so to my knowledge the vertical antenna would almost never be utilized.

Anyways, please post you thoughts on receiver mounting, some photos would be great too!

[Max]

IMHO everything you say makes sense. Any discussion of antenna placement should start with how the Tx antenna is held and the desired angles of coverage (like you say, a 3D acro 'plane would be a lot different from an AQ).

Personally I keep my Tx antenna mostly horizontal (I also often use a patch style since I aim the Tx at the model anyway). I use FrSky and on a bigger model I get their extended antennas. On a smaller build, their stock antennas are long enough to extend past the center plates. Rx is on top with the rest of the stack, but I run the antennas out past the plates and/or down the legs. I keep both antenna tips horizontal, one pointing back towards me, and another pointing 90° off to the right or left. RSSI stays > 80, so I'm happy

-Max

[kinderkram]

Ideally there should only be air between rx&tx antennas.
That´s hard to achieve on bigger copters with gimbal, gears and what not.

Especially if you want to keep the signal wires short, you´re doomed to have the antennas covered in some situations.
That´s where the DSM satellites kick in. With a distribution board you could have 4 of them, attached to certain places to always have a clear view.

[LordPikaChu]

Thanks for your replies guys!

@kinderkram - yeah, having multiple satellite Rxs sounds like a good idea, but I use Graupner MX-16, so I have to stick with what I have now.

Do you think that using longer antennas would help with the reception? I have two 45cm antennas for my GR-16 receiver and I'm thinking about using them for my upcoming 70cm hexa. This way I could lead the actual active element on the antenna to places that are more remote from all the power cables and more visible from pilot's perspective. I'm not sure how to keep antennas this long in place, though. I don't want them flapping around and being cut off by spinning props, but I also don't want to root them along carbon fiber arms, as I've heard that this can detune antennas. Any ideas?

[kinderkram]

Not an easy decision. I think trial&error will be the best approach to find the best solution.
Do some range tests and watch the RSSI while turning the copter around or the receiver away from the craft.