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 MIL-HDBK-419A
10.4.2.4.2 In-Line Waveguide Attachment. Connecting the waveguide to the shield without the feedthrough
section and flange joints requires an in-line connection. In-line connections are somewhat inconvenient,
because the waveguide penetration hole in the facility must be fairly accurately located so that it is aligned
with the waveguide ports on the internal equipment and the external plumbing. In addition, the hole in the wall
must be large enough to pass a waveguide flange, yet must be effectively closed by the attachment mechanism.
Finally, the attachment to the waveguide must accommodate misalignment of the waveguide with the axis of
the hole. If we further prohibit welding or brazing because of the potential distortion and damage to the
internal finish of the waveguide, we are limited to soft soldering, mercury wetting, and clamping to make the
electrical connection to the waveguide. Because of its environmental problems and its tendency to dissolve
waveguide materials, mercury wetting has not been proposed to make the connection. The use of soft solder
bonds also is prohibited by MIL-STD-188-124A on conductive paths subject to lightning or power fault currents.
The following procedures are acceptable for bonding waveguides or cables to a designated RF shield, barrier or
entrance plate.
10.4.2.4.2.1 Sleeve and Bellows Attachment. In this method, illustrated in Figure 10-13, the connection to the
waveguide is made with a snug-fitting sleeve over the waveguide. The sleeve may be installed on the guide
before the end fittings are installed, or a split sleeve may be used so that it can be installed at any time. The
preferred method of attaching the sleeve to the waveguide is to soft solder the sleeve to the guide with a
eutectic lead-tin alloy. For split sleeves, however, it will probably be necessary to provide mechanical support
with a clamp, as illustrated in the figure. If even eutectic soldering cannot be tolerated, a clamping alone may
suffice, if the sleeve is slitted to allow it to grip the waveguide and if the sleeve and waveguide are both clean
and protected so that they remain clean. To help prevent distortion of the waveguide by the clamp, it is
recommended that a neoprene or other resilient cushion be used between the clamp and the sleeve. The flange
on the sleeve and the bellows and its flanges can be welded together without damaging the waveguide. Details
of their design are optional, but the bellows and flanges must be large enough to pass the waveguide flange if
the bellows assembly is to be installed in the field after the waveguide is assembled.
10-21
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