MIL-DTL-15370J
3.4.11.2 Plating. All metal parts of directional couplers which are not corrosion-resistant shall have a plating of
silver, type I or II, grade A, palladium, gold, nickel, or tin, in accordance with ASTM-B700, ASTM-B679, SAE-AMS-
2422, SAE-AMS-C-26074, or ASTM-B545, ASTM-B339, whichever is applicable (see 3.1). The minimum thickness
for gold and nickel plating shall be 10 microinches and 30 microinches, respectively. Aluminum alloy surfaces shall
be chemically treated in accordance with MIL-DTL-5541 or equivalent corrosion prevention method.
Magnesium-alloy surfaces shall be given a chrome-nickel treatment in accordance with type I of SAE-AMS-M-3171.
Nickel plating shall be used only when other plating cannot meet the intended performance requirements.
3.4.11.3 External finish. External finish shall be applied to connectorized or waveguide couplers only regardless of
plating or chemical treatment, except that the mating surfaces shall not be coated. The primer coat shall be zinc
chromate in accordance with TT-P-645. Two finish coats of enamel, in accordance with type III, class 2, of MIL-DTL-
15090, shall be applied. External coating shall be applied as continuous film.
3.4.12 Weight. The weight of the directional coupler shall be as specified (see 3.1).
3.4.13 Temperature range. The operating and non-operating temperature ranges shall be as specified (see 3.1).
3.4.14 Pre-seal bake. Hermetically sealed directional couplers shall have a pre-seal bake in an inert atmosphere
or vacuum at the maximum specified storage or operating temperature, whichever is greater, for a minimum of 16
hours. There shall be a direct transfer to the seal chamber with an inert atmosphere that has a monitored moisture
content of less than 0.1 percent.
3.4.15 Connection cap. All connections that are not normally sealed shall be capped with push-on plastic caps to
prevent both damage and the entrance of moisture and foreign material during shipment and storage.
3.4.16 Threaded parts. All screw threads used in the construction of directional couplers shall be in accordance
with FED-STD-H28.
3.4.17 RF input power to primary. Directional couplers shall be designed to meet the electrical requirements with
the specified RF input power to the primary.
3.5 Performance.
3.5.1 Coupling. When directional couplers are tested as specified in 4.7.5, the measured value of coupling shall
be within the tolerance specified for the nominal value. This specified tolerance includes the allowed variation of
coupling over the specified frequency ranges.
3.5.2 Coupling variation (frequency sensitivity). When directional couplers are tested as specified in 4.7.6, the
variation in coupling (in dB) over the specified frequency range shall not exceed the maximum specified (see 3.1).
3.5.3 Effective directivity. When directional couplers are tested as specified in 4.7.7, the effective directivity (in dB)
over the specified frequency range shall not exceed the value specified.
3.5.4 Insertion loss (see 6.4.2). When directional couplers are tested as specified in 4.7.8, the insertion loss
(excluding coupling power loss) shall not exceed the value specified.
3.5.5 Voltage standing wave ratio (VSWR).
3.5.5.1 Primary line (see 6.4.3). When directional couplers are tested as specified in 4.7.9.1, the VSWR over the
specified frequency range shall not exceed the value specified.
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