BPSK modem 1200. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Data transfer
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When working with packet communication on VHF at high exchange rates, phase modulation (BPSK) is used. The 1200 Baud phase modem (Fig. 1) is connected between the transceiver and the TNC.
Fig.1 (click to enlarge)
The design of the modem is shown in Figure 2-4. Instructions for setting up a phase modem:
1. Check the presence of supply voltage on all microcircuits.
2. Connect a modem to the packet communication controller (pins: TXD, TXCL, RXD, DCD).
3. Check the frequency on pin 9 of D1 (1200Hz).
4. Type on the computer keyboard: "cal", "enter", (the controller entered the calibration mode) "to" (transmission is turned on). By pressing the "D" key, check the presence of frequencies of 1200 and 600 Hz at the modem's THA output (the frequencies change each time the "D" key is pressed). Exit calibration mode - key "Q".
5. Resistor R1 set the level on the engine +5 volts.
6. Connect the pins of the TXA-RXA modem. Check the presence of a signal at the output of the comparator DA 1.1.
7. Replace RIO, R11 with a 200 - 300 kΩ variable resistor. Smoothly rotating the axis of the resistor and observing the waveform at the RXD output with an oscilloscope, achieve identity with the signal on the TXD modem pin (in this case, the controller must be in calibration mode and a square wave with a frequency of 600 Hz must be present at the TXD input).
8. Unsolder and measure the resistance of the variable resistor. Subtract 10 kOhm from the obtained value and solder a fixed resistor of the received value instead of R10.
9. If there is a signal at the RXA input, the DCD LED should go out, if this does not happen, select the position of the R1 resistor slider more precisely within a small range.
Ris.2
Ris.3
Ris.4
Author: V. Chepyzhenko (RC2CA), Molodechno; Publication: N. Bolshakov, rf.atnn.ru
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