Datron TW7000MS, Техническое руководство

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3: Theory of Operation
TW7000MS 3-9
3.4 Receiver Signal Flow
For a block diagram of the receive path in the TW7000, refer to the
"Transceiver Receive Path Diagram" figure on page 3-11. The receive signal
(channel frequency) enters the radio via the 50 ohm antenna connector on the
rear panel, passes through the VSWR board (E4), and goes to the RF Filter
board at J50. In the RF Filter board, the signal is low-pass filtered before
exiting and going to the 75 MHz IF board at J52.
In the 75 MHz IF board, the channel frequency is mixed with the first LO to
form the first IF at 75 MHz, then filtered and amplified before going to the 5
MHz IF board at J53. The signal is mixed with the fixed 70 MHz second LO
to obtain the second IF at 5 MHz, then filtered, amplified, and mixed with the
third LO (BFO) to get to baseband audio.
The demodulated audio (DEMODA) exits the 5 MHz IF at J5-21 and goes to
the Audio board (J8-21). In the Audio board, audio is processed, passed
through the squelch gate, and sent out as unbalanced squelched audio via J8-7
to the front panel (J1-30) to drive the speaker, or to Accessory 2 (pin 22).
Unbalanced squelched audio is provided at J8-6, J18-19 to both accessory 2
and accessory 3 (pins 6 and 13) connectors.
Channel frequency = 1.6 MHz, LSB, voice, 1 kHz modulation
First LO = 75 MHz + channel frequency
= 76.6 MHz
First IF = 76.6 MHz - (1.6 MHz - 1 kHz)
= 75.001 MHz
Second IF = 75.001 MHz - 70 MHz
= 5.001 MHz
Output
Audio = BFO - second IF
= 5.000 MHz - 5.001 MHz
= -1 kHz
Channel frequency = 1.6 MHz, USB, data, 1 kHz modulation
First LO = 76.6036 MHz
First IF = 75.0026 MHz
Second IF = 5.0026 MHz
Channel frequency = 1.6 MHz, USB, data, 1 kHz modulation
Output
Audio = BFO - second IF
= 5.0036 - 5.0026
= 1 kHz