Metalic films and Rx antenna performance
11-13-2003 | 11:13 AM
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From: Lehigh Acres,
FL
Metalic films and Rx antenna performance
What constitutes a threat...and what does not?
Over the years there has been much talk of Rx antenna signal degradation when in close proximity to things such as metal push rods, servos and their leads, etc. How close is too close? Since I am one of those who much prefers to keep the Rx antenna inside the aircraft, I would like to know from the knowledgeable sources, just exactly what constitutes a potential problem and what does not. Metal clevis to a metal throttle arm, is a common item, and the new metalic trim films are an aluminum foil based material...would this form a signal shield? Would only a few metallic trim pieces have any effect on the antenna? If the antenna was external to the aircraft, and the aircraft covered with a metalic foil vinyl, would it also have some effect on the received signal? Thanks for helping to resolve some of these old "wifes tales" that are tossed around every flying site, and helping us to make our radio installations much more reliable, and safer.
Over the years there has been much talk of Rx antenna signal degradation when in close proximity to things such as metal push rods, servos and their leads, etc. How close is too close? Since I am one of those who much prefers to keep the Rx antenna inside the aircraft, I would like to know from the knowledgeable sources, just exactly what constitutes a potential problem and what does not. Metal clevis to a metal throttle arm, is a common item, and the new metalic trim films are an aluminum foil based material...would this form a signal shield? Would only a few metallic trim pieces have any effect on the antenna? If the antenna was external to the aircraft, and the aircraft covered with a metalic foil vinyl, would it also have some effect on the received signal? Thanks for helping to resolve some of these old "wifes tales" that are tossed around every flying site, and helping us to make our radio installations much more reliable, and safer.
11-13-2003 | 05:39 PM
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RE: Metalic films and Rx antenna performance
There really isn't a sure answer for you. The metallic Monokote colors, as well as Aluminum and Chrome Monokote films don't actually contain any metal particles in them. The main problems with the antenna's location is the proximity to other wires: servo and battery leads. They will emit a small electromagnetic field that can interfere with antenna reception.
As far as metal-to-metal contact is concerned, it could be a major problem in the AM systems, but FM systems are more resistance to interference by electrical noise. Metal rubbing (vibrating) against metal can produce electrical noise that the receiver can pick up. Since it's basically AM noise, FM receivers will reject it, unless it's really, really strong. Ignition noise is a strong one, and many times, a gasoline engine's ignition system needs shielding to prevent the noise from getting into the receiver and causing problems.
Long, all-metal pushrods could pose a difficulty if the receiver antenna's too close, but we're talking within an inch or so. Even so, on small gliders, I've run metal cable pushrods the length of the fuselage with the receiver antenna taped to the bottom of the fuse on the outside. The pushrods were no more than an inch from the antenna, and no interference was noted.
If the model is a scale model with actual aluminum sheet as the covering, then it's possible some shielding may occur.
We're sorry, but there's no absolute, sure answer. You make the best installation you can, range test the model with the engine running and not running and see how you do. If the ground range is OK, you fly. If you get glitching, you have to try to see where it came from....antenna blanking, long servo leads, a bad servo feeding back, outside interference, and on and on. We hope you get the picture.
As far as metal-to-metal contact is concerned, it could be a major problem in the AM systems, but FM systems are more resistance to interference by electrical noise. Metal rubbing (vibrating) against metal can produce electrical noise that the receiver can pick up. Since it's basically AM noise, FM receivers will reject it, unless it's really, really strong. Ignition noise is a strong one, and many times, a gasoline engine's ignition system needs shielding to prevent the noise from getting into the receiver and causing problems.
Long, all-metal pushrods could pose a difficulty if the receiver antenna's too close, but we're talking within an inch or so. Even so, on small gliders, I've run metal cable pushrods the length of the fuselage with the receiver antenna taped to the bottom of the fuse on the outside. The pushrods were no more than an inch from the antenna, and no interference was noted.
If the model is a scale model with actual aluminum sheet as the covering, then it's possible some shielding may occur.
We're sorry, but there's no absolute, sure answer. You make the best installation you can, range test the model with the engine running and not running and see how you do. If the ground range is OK, you fly. If you get glitching, you have to try to see where it came from....antenna blanking, long servo leads, a bad servo feeding back, outside interference, and on and on. We hope you get the picture.
