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Receiver Antenna Question


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I am going to make an antenna mount for my Futaba FASST receiver - basically a small mount with two plastic tubes at 90 degrees to keep the antennas tidy and at right angles - it will be fixed to the outside of the plane.

 

Question - so imagine the tubes make a right angle V - is it okay for this V to mounted flat on the top of the fuselage or is it better if it were tilted up at 30 or 45 degrees.

 

I'm guessing it doesn't matter that much as on past aircraft they have just be stuffed inside the fuselage out of sight not even with proper 90 degree orientation - but thought I'd check with the experts here.

 

Cheers,

 

Nigel  

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Flat on top of a fuselage works but probably best not flat 'against' the fuselage if it is carbon or some other conducting material.

The attached photo shows an arrangement that worked OK for me in a carbon fuselage.

 

Dick

Aerial support.JPG

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The underlying theory is that an antenna has a dead zone in the direction the wire is pointing. So a second antenna that is not pointing in exactly the same direction has a different dead zone. 90degrees is best, but the 90 degree pair can then be in any orientation.

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With a carbon fuse I'd be sorely tempted to put one antenna out 45 degrees either side, to avoid the situation where both antennae are capable of being shielded from the transmitter by the carbon fibre fuse.

 

Otherwise I agree with Dad_flyer's explanation, with both antennae as well clear as possible and not parallel to anything that conducts electricity.

Edited by Allan Bennett
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It cannot be that critical. We are talking about a moving receiver. And we are standing below the model as well And a very short wavelength. 90 degrees to what and  in which plane, not meant to be a pun plane meaning

x or y axis. I have seen modellers get their knickers in such a twist about this to the extent that they pull their aerials into all sorts of positions to achieve the legendary 90 degrees .

These aerials are delicate things  Usually the same modellers who have the problems.

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It is indeed not that critical. The dead spot is straight along the antenna wire, so as long as there is some angle between them the two antennas will cover each other's dead spot. The furthest from the same direction is 90degrees, so that is best, but it is not critical.

 

90 degrees to eachother has no reference to the model or receiver, it can be in any plane. Thinking about the best reception rather than the dead spot, the best reception is more like a ring donut with the antenna pointing up the hole. Two of those at 90degrees makes something like a sphere (or a jam donut). Reception is pretty much the same in all directions in that case, which is what we would like.

 

Everyone managed with one antenna on 35MHz... 

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I just place them at 90deg and as far apart as possible and also try to put them on the underside; probably makes little or no difference but thats where most of us will be.

 

Or if its difficult to position just use the antennaless options, havent had an issue and just poke them wherever but away from the usual signal affecting materials.

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