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 MIL-HDBK-419A
Design equipment enclosures that require large inlet and/or outlet apertures to include suitable
d.
shielding such as honeycomb placed over the aperture. Table 3-1 lists typical cutoff and recommended usable
frequencies of standard honeycomb cell sizes. Shielding may also be provided by layers of copper screening
with an attendant lower shielding effectiveness and higher air resistance. The mesh size should offer 60 or
more strands per unit wavelength at the highest frequency to be shielded.
Table 3-1
Frequency Properties of Standard Sizes of Honeycomb
Cutoff Frequency
Upper Usable Frequency
Ceil Size
(in.)
(GHz)
GHz)
1/8
48
16
3/16
32
10.7
1/4
24
8.0
3/8
16
5.3
Mount screens over apertures in the manner shown in Figure 3-24.
e.
Compare the attenuation of various types of screen with the shielding effectiveness required before
f.
choosing the screen to be used.
g.
Shield meters with one of the techniques illustrated in Figure 3-25.
Provide metal caps for fuse receptacles and for phone and meter jacks.
h.
Use fuses, jacks, and receptacles that have metallic bodies where possible.
i.
Shield either the front or rear of pilot and indicator lamps. Shielding of the front may be achieved
j.
through the use of wire screen or conductive glass.
Use equipment enclosures and cabinets to attenuate unwanted signals.
k.
Employ internal modular shielding in specific applications where the enclosure shield is inadequate.
l.
3-30
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