When designing a cabling system for a particular airframe, there are two
basic factors, or requirements, to consider:
(1) What devices in the airframe are susceptible to either steady-state or
transient transmission line effects? This evaluation covers the frequency
spectra of normal signals, transients, and also those frequencies over which
interference and interaction spectra extend. After the susceptible devices have
been isolated, it is necessary to tabulate tolerable threshold levels.
The specific parameters are:
- voltage standing wave ratio (VSWR)
- impedance mismatch (as a function of frequency
- phase shift
- propagation delay
(2) What are the levels of interference and noise signals that can be induced
into transmission lines from the environment or adjacent cables?
Recognizing these requirements, special techniques can be used to reduce
coupling to the susceptible devices.