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Most of the intercoms now have private functions such as CTCSS and DTCSS. Generally speaking, when these private functions are set on the intercom, it is impossible to hear the content of the call without knowing the private line code used, but this is not true voice privacy. Because its security function is not very well, it is only useful for unintentional eavesdroppers but useless for intentional eavesdroppers. For users who need to have confidentiality requirements, they cannot rely on the "private" line for confidentiality.

1. The voice privacy of the wireless intercom system is to disguise the call information

Unauthorized people cannot understand the content of the call, and the disguised speech is called literal words. The process of disguising voice information is called voice encryption, and the encrypted voice information is called secret words. The set of rules and procedures used by the encryptor is called encryption algorithm, and the algorithm is usually carried out under the control of a set of keys. The recipient uses the secret key, which is used to encrypt the opposite algorithm, to restore the encrypted words to the literal words that they can understand. This process is called decryption or deciphering, and the process of deciphering the plain words from the secret words by the eavesdropper is called deciphering.

The voice encryption of the intercom is to process the voice information of the call, destroy its characteristics and reduce its intelligibility. After using the security function, the voice quality will be affected to different degrees, so pay attention to this problem when choosing the security level. Decryption is performed on most secure devices, and voice quality is affected by channel distortion, interference, and background noise. The cost factor should also be considered when choosing a security device. The higher the security function, the higher the cost of the security device. Therefore, various factors such as voice quality, security level, and cost of security equipment should be comprehensively considered when selecting security equipment.

2. The voice security technology of intercom is mainly divided into analog and digital voice security technology

Frequency domain scrambling is the earliest analog voice secrecy technology used in voice, and it is still widely used today. There are three commonly used techniques for frequency-domain scrambling: scramblers, band-shift scrambles, and band-splitting. Mainly use modulators and filters to achieve frequency shifting, frequency measurement and division.

Frequency scramble is the voice security technology that most of the imported wireless intercom systems are used at present. Frequency scramble is to exchange the high frequency and low frequency of the signal, that is, move the high frequency part of the signal to the low frequency band, and move the low frequency part to the high frequency band. The scrambled signal has the same frequency range as the original signal. The frequency components of the original voice signal are scrambled to reduce the intelligibility and play the role of voice secrecy. The same frequency scrambler is used to restore the signal at the receiving end. This frequency scrambler is the simplest speech scrambler, which is essentially an encoder. Commonly used scramblers do not have keys, so their secrecy is limited.

In addition, there is a frequency band-shift scramble, which is based on a frequency scrambler to introduce a key, and both parties to the call can use the agreed key for confidential communication. In this way, the band-shift scrambler becomes a real voice secrecy machine.

There is also a frequency band division, also known as frequency band scrambling, which is also the most commonly used technology in analog voice security machines.

The security of the digital voice security technology of the wireless intercom system is very good. Moreover, this system overcomes the difficulty of keeping density and voice quality in the analog voice security technology, so most of the digital voice security technology is used in important occasions.

Digital security systems include voice codecs, decoders, digital modulators, demodulators, and channel coders and decoders. The working principle is that the analog voice signal is digitally encoded into a digital signal through a voice encoder, and then converted into a digital encrypted voice signal through an encryptor, corrected by a channel encoder, and then transformed into a digital signal suitable for the sending end through a digital modulator. The analog signal transmitted by the channel. At the receiving end, the demodulator is restored to a digital signal, and then the voice signal is restored by a channel decoder, a decryptor, and a digital-to-analog converter.

The encrypted signal output by the digital voice security technology has pseudo-random characteristics, so it is only a piece of noise for eavesdroppers, which cannot be understood.