Nuisance interference has occurred between licensed transmitters and aircraft for many years, and up to now it has not caused any serious problems to the continued safe flight and landing of commercial aircraft. To ensure continued flight safety with new electronic technology avionic systems, new design methods are needed. This paper addresses some of the more important design techniques for complying with the new HIRF requirements.
HIRF design measures have to consider the “weakest link” when assessing systems. One or two improper design measures can nullify all of the beneficial hardening techniques of the system. Today's equipments are neither analog nor digital, but a combination of both. All design measures must be compatible with both sets of rules. Employing older proven analog design measures to prevent “ground loops” is no longer sufficient for the new digital/analog combination systems. New rules that satisfy both the low frequency, limited bandwidth, analog circuits and the wide bandwidth digital functions must now be implemented.