Packet modem. Scheme, description

Packet modem. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Nodes of amateur radio equipment

In my previous article [1], a packet modem scheme was published for operating in the VHF band at a speed of 1200 baud. Somewhat later, the circuit was successfully tested for operation in the KB range at a speed of 300 Baud. which allowed the development of a universal 1200/300 baud modem. characterized by simplicity and reliability.

(click to enlarge)

Schematic diagram of the modem is shown in the figure. Compared to [1], it has not undergone significant changes, with the exception of two points: switching nodes for the frequency of the reference oscillator 4.43 MHz / 2.215 MHz and indications of the PTT and DCD modem operation modes have been added, providing additional convenience in operation. Switching between KB and VHF modes (speeds 300/1200 Baud) is performed by switch SA1.

Connector X1 is used to connect to the computer's COM port, connector X2 - to connect a KB transceiver, connector X3 - to connect a VHF radio station.

In addition, I would like to clarify the data on the circuit diagram [1]: the value of the resistors R2 and R14-2.2k0m.

Literature

1. Teteryuk V. Modem for the package. Radio amateur. - 1997. No. 10. P.37.

Author: V. Teteruk (YL2GL), LV-5402, Latvia, Daugavpils; Publication: N. Bolshakov, rf.atnn.ru

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