Does the MAAA have recommendations on how to construct a safety fence to protect pilots from runway operations?
The MAAA cannot recommend the construction of safety fences that include metal framing or panels, although many Clubs do operate with these types of fences with no apparent problems. The reasons for this include:
- Conducting material reflects radio waves.
- The better the conductor the more effective the reflector.
- This is the principle behind the Faraday cage that provides complete Electro Magnetic Radiation screening and is also the basis of the design of TV antennas.
- If items are placed at random it is difficult to predict the effect without sophisticated modelling.
- The effect depends on the frequency, the location of the transmitter and receiver antennas and their orientation, and the size, shape and position of the reflector.
- This is why model radio range testing in the proximity of cars and wire fences gives unreliable results with variations of at least 50% in range having been observed.
- Rust and high resistance connections can make the situation worse by generating spurious signals and in-band 3rd Order Intermodulation. Operation at 29, 36 and 40 MHz frequencies are a particular concern.
- Due to the unpredictability and unreliable repeatability of the interference it is impossible to know if any radio problems were either caused by, or exacerbated by, metal fences when they are used.
- The more the metal there is around and the more the transmitters are enclosed by metal the higher the probability of issues arising.
- Metal behind or to the side of the transmitters will affect the outcome as well as metal in front.