G. This Headset-Microphone Kit is designed to fit both the regular and large size Combat Vehicle Crewman\'s Helmet. The electrical characteristics of the kit are compatible with Tactical Radio Systems, such as the VRC-12.

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MIL-DTL-55535A

3.4 Finish. Equipment shall be finished, as specified in MIL-F-14072, type I.

3.5 Marking. Marking shall conform to MIL-STD-13231.

3.5.1 Serial numbers. Serial numbers are not required.

3.6 Microphone.

3.6.1 Microphone response. The frequency response of the microphone shall be essentially flat from

300 to 3,500 Hz. The minimum power output of the microphone shall be � 56 dBm (the term "dBm" is

used, when a power of one milliwatt is the reference level) at 1,000 Hz, when measured in accordance

with 4.7.1. In addition, the response shall fall within the envelope on figure 1. During this test, the

microphone shall be terminated with a non-inductive load of 150 ohms.

3.6.2 Distortion. Total harmonic distortion shall not exceed 5 percent at a sound pressure level of 115

dB referenced at 20 �Pa (micropascal) over the frequency range of 300 to 3,500 Hz (see 4.7.2).

3.6.3 Signal to noise ratio. The signal-to-noise ratio of the microphone shall be at least 15 dB

(signal over noise), when measured in accordance with 4.7.3.

3.6.4 Dielectric strength, and insulation resistance (see 4.7.4). There shall be no evidence of

insulation breakdown. There shall be no decrease in insulation resistance below 1 megohm following this

test.

3.7 Earphone. The earphone element shall be constructed in accordance with ECOM Drawing SM-C-

436361.

3.7.1 Earphone response (see 4.8.1). The output of the earphone shall be not less than 103 dB above

a reference level of 20 �Pa, when 1 milliwatt rms power at 1,000 Hz is applied to the earphone terminals.

The response of the earphone at any frequency shall not deviate from the 1,000 Hz response by more

than the values shown in table I (see figure 2).

TABLE I. Earphone response.

Deviation from 1,000 Hz (dB)

Frequency (Hz)

Min.

Max.

300 - 1,000

-3.5

+1.5

1,000 - 3,500

-5

3.7.2 Distortion. The acoustic output of the earphone shall have no more than 5 percent total

harmonic distortion over the audio frequency range of 300 to 3,500 Hz, when measured as specified in