Quantcast Lower Frequency Equipments

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Components exhibit different degrees of susceptibility to damage from EMP (see Volume I, Chapter
10). Electromechanical devices appear to be the least susceptible.  Vacuum tube devices offer reasonable
immunity, while solid state devices such as diodes, transistors (FET's -Field Effect Transistors- in particular),
silicon controlled rectifiers, and integrated circuits exhibit damage susceptibility thresholds two to three orders
of magnitude less than the threat posed by the EMP. These factors should be kept in mind during initial design
and, wherever a circuit function can be accomplished with a less susceptible device, use the device with greater
immunity.  For example, an electromechanical relay will be less likely to suffer damage than will an SCR
(Silicon Controlled Rectifier) or transistor switch. A vacuum tube front end for a receiver will offer greater
immunity than will the transistor version. Where the more susceptible devices must be used, they should be
adequately shielded (the compartmentalization of subassemblies is probably the most economical and practical
approach) with appropriate surge protection applied to all incoming and outgoing leads.
Effective EMP design practices require careful tradeoff comparisons between functional
requirements, device properties, physical constraints, and overall cost.  Consult Volume I, Chapter 10 for
additional design assistance; References 3-6 and 3-7 are also highly recommended.
Before installing, or accepting for installation, any piece or item of electronic equipment in a facility designed
or modified to meet the recommendations represented herein, the equipment should be evaluated for
conformance with the practices set forth in this volume. Record the results of this evaluation on the Inspection
Form given in Section 3.7.11.
Before beginning the evaluation, determine whether the equipment is designed to operate at frequencies
(a) from dc to 30 kHz (in some cases up to 300 kHz), or (b) above 300 kHz (in some cases down to 30 kHz).
Square wave signals are always considered to be higher frequencies. In making this determination, the primary
signals to consider are those which interface or communicate with other equipments or systems. For example,
the frequencies of control and monitor signals, communication signals, data links, and input and output rf
signals should be noted. (Those signals arising from internal sources and utilized only internally to a unit or
piece of equipment are primarily the designer's responsibility.) List the frequencies under Part IA of the
Inspection Form.
After establishing the frequency classification of the equipment, inspect the lower frequency types for
conformance with the recommendations set forth in Section and inspect the higher frequency types for
conformance with the recommendations contained in Section Some equipments will necessarily utilize
both lower and higher frequency signals for interfacing purposes. For example, wideband data links frequently
extend from low audio frequencies to frequencies well above 10 MHz. Such hybrid systems should be inspected
for conformance to the recommendations set forth in Section Specific inspection steps and procedures
for all three types of equipments are contained in the following sections.
3.7.1 Lower Frequency Equipments.
Examine the drawings and schematics and visually inspect to see if an isolated single-point signal
ground as described in Section is provided. Provide a brief description of the signal ground network
under Part IB of Inspection Form or attach copies of the schematics or drawings. Verify that the internal signal
ground network is terminated to an insulated signal ground terminal of a type described in Section


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