MIL-DTL-18266C
3.3.11 Cord assembly. Cord: P/O H-87B/U shall be assembled as shown pictorially and schematically
on figure 1. After assembling the transformer within the transformer-plug shell, the remaining space
within the shell shall be filled with a suitable epoxy resin. The assembled transformer-plug shall be
protected by rubber molding to a depth of not less than 0.025 inch. The junction of the single and multi-
conductor cordage shall be protected and reinforced by a rubber molding. In addition, the junction
molding shall include an eyelet for attaching the cord to the helmet. The dimensions of the finished cord
shall be in accordance with figure 1.
3.3.12 Total weight. The total weight of each cord shall be no greater than six ounces.
3.3.13 Recycled, recovered, or environmentally preferable materials. Recycled, recovered, or
environmentally preferable materials should be used to the maximum extent possible provided that the
material meets or exceeds the specified requirements (see 3.1), and promotes economically
advantageous life cycle costs.
3.4 Performance.
3.4.1 Frequency response (see 4.6.4). The frequency response characteristics of the transformer shall
be smooth and free from abnormal irregularities over the frequency range of 200 to 6,000 Hz. The output
response over this frequency range shall be within ± 2 dB of the 1,000 Hz output.
3.4.2 Distortion (see 4.6.5). The distortion introduced by the transformer shall not exceed 2 percent for
frequencies between 1,000 and 6,000 Hz. The distortion may increase for frequencies below 1,000 Hz,
but, shall not exceed 15 percent at 200 Hz.
3.4.3 Impedance (see 4.6.6). The impedance of the primary and secondary windings over the
frequency range of 200 to 6,000 Hz shall not deviate from the 1,000 Hz values by more than 15 percent.
3.4.4 Overload (see 4.6.7). The cord (transformer) shall be able to withstand an overload of 500
milliwatts rms at 1,000 Hz for a period of 8 hours without signs of failure. After meeting this requirement,
3.5 Environmental.
3.5.1 Flame-retardant cord (see 4.5.4). Self-sustained combustion of the finished cord insulation shall
not progress at a rate in excess of 1 inch per minute.
3.5.2 Temperature requirements.
3.5.2.1 Operating range. The cordage shall be flexible and resilient throughout the temperature range
of 55 degrees to +85 degrees C (-67 degrees F to +185 degrees F).
3.5.3 Humidity (see 4.6.8). The cord shall be able to withstand an ambient humidity condition of 95
percent, relative at 50 degrees C (122 degrees F). After meeting this requirement, the cord shall meet
the requirements of 3.4.1.
3.5.4 Cold bend (see 4.5.7). Specimens of the cordage shall show no evidence of cracking or other
damage to the jacket or conductor insulation after being subjected to a cold bend test. Immediately
following the cold bend test, the specimens shall withstand without breakdown a modified version of the
dielectric withstanding voltage test of MIL-DTL-10392.
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