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I'm currently building a rc radio system using the 433mhz RFM69W transceiver, so far everything works fine, but i am not sure about the way i laid out my antenna and how the layout cripples the efficiency of it. (The connection is stable up to 400m to 600m with a building in between at ~13dbm output power)

this is a crude but very accurate drawing of the layout

The wires are each around 165 mm long to form a quarter wave monopole, the layout in the re-purposed radio is exactly like in the schematic above.

My main concern is the bend in the antenna and the positioning of the ground wire, would you recommend a different antenna design (helical/pre-made?), keeping in mind that the joysticks eat up most of the room except for a few shafts in the middle/sides of the housing just like here:

example (not my picture, but the rc controller he built this in is laid out just like the one I am using)

And would it make a big difference at all?

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I'm not experienced with RC systems, but on general antenna design principles:

  • The bend is fine. It's too small a feature to have much effect.
  • The “ground” wire (really better described as a second antenna element) is fine. The antenna will radiate better in the direction that wire runs than others.

The biggest problem with this layout is that your antenna is going to be obstructed by the user's hand. You would get better results by using an antenna which extends away from the controller's casing.

If you don't want to do that, I would suggest swapping the roles of the two wires. Assuming your antenna “GND” is tied to the circuit ground of the rest of the controller, that circuit ground is already somewhat capacitively coupled to the user's hands, so it's best to put the other pole of the antenna in the least-coupling position.

However, this theoretically gives you a horizontally polarized antenna instead of vertical-or-45°-depending polarization, which might be worse — how much polarization matters depends on how reflective the environment you're operating in is.

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  • $\begingroup$ Thanks for your input! I'll try re-positioning the radio module to the top and rotating the radial(s) so that they point forwards, in case the signal turns to be too weak/unreliable in flight. Having everything inside the case is very convenient though since it's compact and you can't break anything... $\endgroup$ – VaTTeRGeR Nov 4 '16 at 22:17
  • $\begingroup$ Gret answer, @G6YO. In AM broadcasting we have to have 120 radials spaced at 3 degrees, but sometimes route them around small structures on the land. And if one side of the land is too short the radials are laid by bending them along the property line and keeping them spaced from each other. But always full length. As long as your radial layout is roughly circular in total the FCC doesn't even need to issue STAs for that because it is so common. $\endgroup$ – SDsolar Apr 14 '17 at 6:36

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