LM I812 is a complete ultrasonic transceiver designed on a block chip. It is used in various pulse echo ranging applications. The work of the chip is carried out by transmitting oscillatory pulses by means of a converter. Then use the same converter to monitor the returned echo. If the received echo signal has sufficient amplitude, the LM1 8 I2 detector will send a pulse with the same width as the original pulse. The closer to the blocking object, the shorter the return echo time received. Ultrasonic transducer drive and receiving circuit composed of LMISI2: 
PufangTech`s VHF radio modems operate in 136~174MHz and 220~240MHz frequency band. The VHF Radio Modem has an air data rates of 19200bps in 25kHz channel spacing and 9600bps in 12.5kHz.
Suitable to apply in data collecting, and VHF radio modems have been used to transmit voice and radio data since the middle of last century. This is one of the most efficient ways to communicate over miles away. A wider coverage is a different advantage belongs to VHF frequency from the others. VHF has 30 to 50 per cent larger range than UHF Radio Modem with the same carrier power.
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