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TX/RX Antenna Orientations

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dknguyen

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My questions is about the difference between antenna radiating strength and polarity.

See my attached graphic.

Blue Antenna = TX
Green Antennas = RX
Let's call the RX antennas 1 to 4, from left to right.

All RX are in the same plane as the radiating field of the TX so they are all sitting in the strongest part of the field.

RX1 won't have any reception. Although RX1 is sitting in the strongest part of the TX field, the TX is sitting in the weakest part of the RX1's field (the blind spot at the tips).

RX2 and RX3 also won't have any reception? Because it is not perpindicular to the radiating disc? Would it not be like trying to induce current flow in a wire by moving a magnet along it rather than across it?

RX4 will receive optimally because antennas transmit the same way they receive and RX 4 is oriented in the field the same way the TX is.

I am fairly sure about RX1 and RX4 (basically both antennas have to mutually be in the strongest part of each other's field for optimal reception). But I am not sure about RX2 and RX3 since they are sitting in the strongest part of each other's field, but they are oriented differently wrt to each other's radiating discs. I ran by some graphics from the Spektrum RC website that, if taken at face value would impy that RX2 and RX3 would work.
http://www.spektrumrc.com/Content/Images/Tech/eliminatesBlind2.gif

EDIT: I also found this neat graphic:
File:Dipolentstehung.gif - Wikipedia, the free encyclopedia
So from the blue lines in the capacitive plates and the red lines being perpindicular to AC current flow, I suppose it would be correct to say that the blue lines represent the electric field and the red lines represent the magnetic field. So reworded, my question would be...for an antenna (a dipole one anyways) to optimally receive it MUST be perpindicular to the radiated magnetic field (or parallel to the electric field). Makes complete sense now that I say it aloud and have a graphic to look at.
 

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k7elp60

Active Member
RX2 will receive some energy, but it is not the same electrical length as RX4.
The other RX antenna's will receive energy, but it will be typically 20db below RX2.
Most energy is transferred between TX and RX antenna's when they are the same polarization.
 
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dknguyen

Well-Known Member
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I suppose my graphic wasn't as clear as I thought it was. Please assume all RX are the same length. RX1, 2, and 3 are supposed to be lying on their side while RX4 is vertical (parallel to the TX). THe only reason it's longer is so you can tell it's vertical (look closely at how the field lines overlap or get overlapped by all antennas to indicate whether or not it is lying in the plane of the field, or poking through it.)

DOes this change your response?
 
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microtexan

New Member
RX2 will receive some energy, but it is not the same electrical length as RX4.
The other RX antenna's will receive energy, but it will be typically 20db below RX2.
Most energy is transferred between TX and RX antenna's when they are the same polarization.
I thought it was 30dB for cross polarized antennas:confused:
 

i_build_stuff

New Member
I think the reception of a dipole is related to the cosine of the angle between it and the electric component of the radiated field. If the antennas aren't completely aligned, but point in the same general direction, then you will get reception that's almost optimal.

The two antenna thing will work to eliminate the sensitivity to direction of a received signal, but only if you use two receivers. Just connecting the antennas together would make the received signal cancel itself out in two new directions...
 
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