(VF): Pertaining to those frequencies within that part of the audio range that is used for the transmission
Note 1: In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz.
Note 2: In telephony, the bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands. Synonym voice band.
Source: from Federal Standard 1037C and from MIL-STD-188
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