2.4 Antenna orientation

There still seems to be confusion on how to best orient the transmitter antenna on 2.4Ghz radios. Even pictures of “correct” and “not correct” antenna positions shown on the Team Horizon website differ from verbal recommendations from various experts. The stubby 2.4 antennas rotate at the base from horizontal to vertical as well as 360 degrees on their axis, resulting in an almost infinite number of ways to point. Our local JR rep made a presentation at a recent club meeting that seems to clear up the issue. In this short article I will attempt to put in layman’s language what the rep explained in fairly technical terms. For starters, both 72Mhz and 2.4Ghz antennas operate in a similar manner. Both are “common”, one quarter wavelength, dipole antennas with omnidirectional radiation in the plane perpendicular to their axis. In lay terms, that means they consist of a straight rod and radiate in all directions outward from the axis of the “rod”. The area directly off each end (axis) of the antenna is a “null” where the radiation pattern is weakest. Think of the radiation pattern as a very fat donut with the antenna pointing through the hole of the donut. Figure 1 shows a technical drawing of a dipole antenna radiation pattern.



Radiation pattern for both 72 and 2.4 transmitters. The “z” axis represents the antenna with nulls on both ends.

The objective is to orient your antenna to keep your jet in the “fat” part of the radiation pattern and away from the “hole” or null off the end. To achieve this, always have your antenna perpendicular to the anticipated flight path. For a 2.4 transmitter this can best be accomplished with the antenna positioned to near perpendicular (bent) and pointing at your head. One null is directly behind you and the other points into the ground immediately in front of you, two areas where hopefully you won’t be flying! If you naturally hold your transmitter pointing downward, the same effect can be achieved by positioning the antenna straight out and pointing at the ground.



Proper 2.4 transmitter antenna position




A logical question at this point is “if my 72Mhz antenna radiates the same as a 2.4Ghz, why aren’t we concerned about it’s orientation”? The answer lies in the wavelength difference between 72 and 2.4. With a wave length more than 10 times longer, the 72Mhz signal has more area to be “seen” by the equally long receiver antenna and in effect, “bends” around objects such as turbines and other solid items in your jet. Because of this characteristic, 72Mhz radios are less susceptible to signal loss in the null portion of the antenna radiation pattern.

Another byproduct of the short 2.4Ghz wavelength is the necessity for multiple receiver antennas. Both JR and Futaba systems use multiple, short antennas and both recommend they be oriented 90 degrees to each other. With Futaba’s two antennas coming out of the receiver, this means they should “point” more or less perpendicular to each other. JR uses up to four remote antennas and they should be placed in different areas in the fuselage and in different orientations as well. The objective with both systems is to have a least one antenna with a clear path to the transmitter signal radiation pattern. My personal opinion is that for most of our installations and the relatively close distance we fly our jets, the orientation of the transmitter antenna is probably not that critical. I see lots of pilots flying with their 2.4 antennas pointed in all sorts of directions and for the most part, nobody is having problems. Nevertheless, why not operate your radio in the most efficient and effective manner possible? We never know when that perfect combination of negative factors will coincide and we end up with a loss of signal. Now that I have at least a rudimentary understanding of how my antenna works, I make sure to keep the strongest signal pointed at my jet.