This information is provided as a guide for shielding your aircraft for
the successful installation and operation of any AM radio system.
Engines used in ultralight aircraft are traditionally two stroke 20 to 75 horse-power units which use a magneto to generate electric current in order to produce a high energy spark for ignition. This type of ignition is reliable and effective and used on most aircraft
utilizing gasoline-fueled engines.
However, this set-up interferes with radio broadcasting. The problem with high energy spark ignition is its inherent characteristic of broadcasting a complete spectrum of radio signals in the form of static, especially on the AM band.
Years ago, when aircraft communication was initiated, the only radios available were of the amplitude modulation (AM type). Since that time, no major changes in aircraft radio design have been made.
Engine ignition noise (static) has always been a problem for aircraft communication systems, and it
remains so today. With the advent of the all-metal airplane, the problem has been reduced for a number of reasons.
Most important of these is the complete shrouding of the engine in a metal cowl with a metal firewall between the engine
and radio installation.
But even shrouding the engine in metal does not remove all of the interference. By shielding the actual source, most unwanted signals can be suppressed. High tension wires should be shielded with wire braid, spark plugs jacketed in metal, and the magnetos housed in a metal case with all of these grounded to the engine block.
As a final measure, the antenna for the radio
should be placed some distance from the engine and connected to the radio with a shielded coaxial cable which has its outer braid
grounded at j each end.