| 摘要 |
FIELD: physics; teaching. ^ SUBSTANCE: invention relates to diving and specifically to diving hydroacoustic (underwater) communication stations. The subject of invention is design of a secure hydroacoustic communication system for divers with a frequency modulated or frequency-shift keyed noise-like signal. In the transmitter, an audio signal in telephony or telegraphy mode is transmitted after a low-frequency amplifier to a carrier-frequency generator and then frequency modulated. This frequency modulated signal is then transmitted to a balanced modulator to whose other input is transmitted a noise signal from a noise generator or a special water noise receiver. A double-sideband suppressed carrier noise-like signal is obtained at the output of the balanced modulator. This signal is amplified by a broad-band power amplifier and emitted into the water using an acoustic antenna. The noise-like hydroacoustic signal is transmitted through a receive path from the antenna to the input of a broad-band limiting amplifier (or several limiting amplifiers which cover the entire band), which cuts off all amplitude noises. The signal is then detected using an amplitude detector without restoration of the carrier. As a result, a signal with frequency equal to double the carrier frequency is obtained at the output of the detector. The signal is formed after merging the lower and upper sidebands of the noise-like signal. This double carrier is frequency-modulated by an audio signal as well as main initial carrier in the transmitter. The signal is isolated using a filter and transmitted to a frequency detector. Low frequency is obtained at the output of the detector which is transmitted to telephone of the diver after amplification. ^ EFFECT: system is simple, compact and cheap, and is characterised by high noise immunity. ^ 4 dwg |
