DX7 Antenna angle?

[Zoobie]

I read somewhere in one of the Futaba ADs, that most of the signal for a 2.4ghz radio comes out the side of the antenna. Does this mean that on your DX 7 it would be safer to fly with the antenna at 90 degrees? Is the knuckle only there so that it fits in flight boxes etc, or is it more important?

Thanks.

[WayneBrown]

its more important.
We generally lock the antenna at about a 45 degree angle, and so far have had no range issues.

[jeffk]

Honestly, it really shouldn't matter at all which way you have it. To get the maximum signal strength between any receiving antenna and any transmitting antenna, the two antennas should be aligned along the same axis. That is, they should be pointing the same direction. We radio folks refer to this a s "polarization". If your antenna on your model is vertical, it will "hear" your transmitter best if the TX's antenna is also vertical. Likewise with a horizontally polarized antenna, but here we introduce another axis: azimuth (the direction the tip of the antenna is pointing).

If your antenna on the TX is horizontal, and pointing at, say 270 degrees (due West), then your receiver will hear it best when it's antenna is also horizontally polarized and pointing at 270 degrees. Signal strength is always lowest when the transmitting antenna and the receiving antenna are "cross-polarized" or put another way, perpendicular to each other.

The thing with antenna placement is, your model's position (and therefore, the antenna's position) is constantly changing as it moves and maneuvers through the air. Therefore, the orientation of one antenna to the other is constantly changing, and so the received signal strength at the model is constantly fluctuating. So, it really matters very little which direction your transmitting antenna is placed. The radios are engineered so that in a worst case scenario (i.e. TX and RX antennas perpendicular and model at outside edge of range) the radio signal strength will be sufficient to maintain control of the model.

Proper antenna / receiver placement in the model will have a much bigger effect on range and signal strength than whether or not your TX antenna is horizontal, vertical, or somewhere in between. Ensure that your antenna is as exposed as you can get it and keep it away from conductive surfaces that can block reception and you'll be fine.

[Pinecone]

Dipole antennas (which is what we use, a quarter wave whip is half of a dipole with the ground acting as phantom second dipole element) do not radiate directly off the tip. So if you point the antenna tip directly at the model, you have the minimum signal going to the model.

But the radiation pattern of a dipole is like a fat donut, so even 3 - 5 degrees angle off the tip has a good signal strength.

[Danal Estes]

There seems to be two groups of people with regard to "bending" or "aiming" the antenna:

Those who read the internet and carefully set various angles into things.

Those who don't read the internet and just go fly with the antenna in whatever orientation.


After watching many, many, many people in both groups, they seem to get about equal results in the real world at the flying field. :)

[WayneBrown]

Heres my validation, Watch someone fly. most folks face the machine, pretty common. Some folks use body english and twist and turn too. With Pinecone's description of a dipole antenna in mind, you are most likely one of the folks who FACES the model you are flying, directly in the weakest plane of signal. Crank the antenna at an angle, and you always have the antenna pointed elsewhere besides the model.
Back in the day of AM radios, you'd get by with pointing the antenna at a model for a couple hundred feet, and lose it. Rotate the tip 90* and regain control. Lessons learned then still apply in some respect to the newer technology.

[jeffk]

A 2.4 GHz antenna on a spektrum or futaba radio is not a dipole by any stretch of the imagination. Unless you're 3 inches tall, the ground is so far away from the antenna (electrically speaking) that there's no possible way it can act like the second leg of a dipole. If anything, it's using the circuitry in the radio, or even the carrying handle as a ground plane.

In any case, an antenna such as we have on our transceivers is so inefficient that we as average users couldn't possibly begin to plot the radiation pattern. With all the pattern interfering objects in the way (not the least of which is your body, which distorts e-fields at 2.4G quite effectively) you might as well give up on predicting where your signal strength is maximum. Also, you're very rarely pointing the tip of the antenna directly at the model. this is why I maintain that polarization would be the only real factor that you could do anything about, but even if you did, a moving model negates anything you CAN do.

If you're really in doubt, do a range test. Try the antenna in various positions, pointing at and perpendicular to the model. To simulate the relative antenna position, move your transmitter to different angles relative to the model. Turn the model around from all angles. This ought to give you a pretty good picture of what's going on.