8571—Technical description
344
NGT Transceiver System Technical Service Manual
300 Hz control tone—generation and detection
The 300 Hz control tone is generated by the tone generator IC16 on the Microprocessor
& TCVR Interface PCB. The clock frequency of 3.579 MHz is supplied from the
oscillator in the Bell 103 modem (IC6) and connected via buffer IC1e to the three clock
inputs of the tone generator (pins 9, 15, and 18).
The internal dividers of IC16 are programmed by the microprocessor via the eight data
lines and initiated by the two address lines (A0, A1) to produce a 300 Hz and two 30 kHz
square wave outputs.
The first 30 kHz from the tone generator (pin 17) clocks the notch and digital filters
(Dual Line Equaliser PCB, drawing
The 300 Hz square wave from the tone generator (pin 10) is applied via an RC network
to the input of a digital LPF IC17 (pin 8). The second 30 kHz square wave from pin 13 is
connected to the clock input (pin 1). The 300 Hz (pin 10) runs continuously, but the
30 kHz (pin 13) is enabled only when the 300 Hz sine wave is required at the output of
the digital LPF (pin 5). The digital filter is disabled when the 30 kHz is removed.
From the output of filter IC17, the control tone is connected to the input of the mixer
amplifier in the Bell 103 modem IC6. From the output (pin 17), the signal is passed via
connector P1 pin 30a to the Rx audio bus on the Backplane PCB, and continues on the
same path as the Rx audio through the Dual Line Equaliser PCB to the output of the
8571.
The 300 Hz received from the master 8571 is connected via the 2-wire or 4-wire
interface and Backplane PCB to the Dual Line Equaliser PCB and follows the same path
as the transmit audio to the output of the hybrid amplifier IC101a (see
). At this point, the 300 Hz control tone (when in the Transmit mode)
is applied to a 300 Hz digital BPF IC106.
The digital filter consists of two sections, the first connected as an LPF, followed by the
second as an HPF. The two filters overlap each other, resulting in a very narrow BPF
centred at 300 Hz. This removes the transmit audio but retains the 300 Hz control signal.
The 30 kHz clock is supplied from the tone generator IC16 on the Microprocessor &
TCVR Interface PCB.
From the output of the BPF, the control tone with the transmit audio removed is passed to
a DC gain-controlled amplifier IC104a. The gain of this amplifier is set by the
microprocessor for 6 dB above the threshold of the 300 Hz detector described below.
The gain-controlled element in amplifier IC104a is a variable resistive cell (delta G). Its
resistance decreases as the DC current is increased at the control pin 1 (controlled by the
microprocessor via DAC IC2 (Dual Line Equaliser PCB). Because the resistive cell is
part of the input circuit to the amplifier, a rise in DC current at IC104a pin 1 results in an
increase in the amplifier gain.
Summary of Contents for NGT 2010 RF
Page 87: ...03 01032 Issue 2 ...
Page 88: ...03 01032 Issue 4 ...
Page 97: ...03 01126 ...
Page 98: ...03 01190 ...
Page 428: ...04 03223 ...
Page 429: ...04 03562 CODAN ...
Page 430: ...04 03437 ...
Page 431: ...04 03533 ...
Page 432: ...08 05513 ...
Page 433: ...08 05514 sheet 1 ...
Page 434: ...08 05514 sheet 2 ...
Page 435: ...08 05628 sheet 1 ...
Page 436: ...08 05628 sheet 2 ...
Page 437: ...08 05628 sheet 3 ...
Page 438: ...08 05628 sheet 4 ...
Page 439: ...04 03125 ...
Page 440: ...08 05300 ...
Page 441: ...08 05522 ...
Page 442: ...08 05523 ...
Page 443: ...08 05524 ...
Page 444: ...04 03201 ...
Page 445: ...08 05470 ...
Page 446: ...04 03423 ...
Page 447: ...08 05986 sheet 1 ...
Page 448: ...08 05986 sheet 2 ...
Page 449: ...04 03133 ...
Page 450: ...08 05317 ...
Page 451: ...04 03109 ...
Page 452: ...08 05266 ...
Page 453: ...04 03108 sheet 1 ...
Page 454: ...04 03108 sheet 2 ...
Page 455: ...08 05265 ...
Page 456: ...04 03106 sheet 1 ...
Page 457: ...04 03106 sheet 2 ...
Page 458: ...04 03106 sheet 3 ...
Page 459: ...08 05261 sheet 1 ...
Page 460: ...08 05261 sheet 2 ...
Page 461: ...04 03095 ...
Page 462: ...08 05235 ...
Page 463: ...04 03378 sheet 1 ...
Page 464: ...04 03378 sheet 2 ...
Page 465: ...04 03378 sheet 3 ...
Page 466: ...04 03378 sheet 1 ...
Page 467: ...04 03378 sheet 2 ...
Page 468: ...04 03378 sheet 3 ...
Page 469: ...08 05889 sheet 1 ...
Page 470: ...08 05889 sheet 2 ...
Page 471: ...08 05889 sheet 1 ...
Page 472: ...08 05889 sheet 2 ...
Page 473: ...04 03410 ...
Page 474: ...04 03414 ...
Page 475: ...08 05963 ...
Page 476: ...08 05962 ...
Page 477: ...08 05973 ...
Page 478: ...04 03169 ...
Page 479: ...08 05415 ...
Page 480: ...08 05416 ...
Page 481: ...08 05511 sheet 1 ...
Page 482: ...08 05511 sheet 2 ...
Page 483: ...04 03369 ...
Page 484: ...08 05869 sheet 1 ...
Page 485: ...08 05869 sheet 2 ...
Page 486: ...08 05869 sheet 3 ...
Page 487: ...08 05910 sheet 1 ...
Page 488: ...08 05910 sheet 2 ...
Page 489: ...04 03542 ...
Page 490: ...08 06461 sheet 1 ...
Page 491: ...08 06461 sheet 2 ...
Page 492: ...08 06461 sheet 3 ...
Page 493: ...08 05910 sheet 1 ...
Page 494: ...08 05910 sheet 2 ...
Page 495: ...04 03425 ...
Page 496: ...08 05988 sheet 1 ...
Page 497: ...08 05988 sheet 2 ...
Page 498: ...04 03424 sheet 1 ...
Page 499: ...04 03424 sheet 2 ...
Page 500: ...08 05987 ...
Page 501: ...04 03499 sheet 1 ...
Page 502: ...04 03499 sheet 2 ...
Page 503: ...08 06261 sheet 1 ...
Page 504: ...08 06261 sheet 2 ...
Page 505: ...04 03498 sheet 1 ...
Page 506: ...04 03498 sheet 2 ...
Page 507: ...08 06260 ...
Page 508: ...04 03379 ...
Page 509: ...08 05890 ...
Page 510: ...15 10506 001 ...
Page 511: ...15 10514 001 ...
Page 512: ...04 03110 ...
Page 513: ...08 05267 ...
Page 514: ...04 03514 ...
Page 515: ...08 06320 ...
Page 516: ...04 03272 ...
Page 533: ...03 01138 ...
Page 534: ...03 01139 ...
Page 604: ...04 03422 ...
Page 605: ...08 05985 ...
Page 606: ...04 03419 ...
Page 607: ...08 05997 ...
Page 608: ...04 03420 ...
Page 609: ...08 05999 ...
Page 610: ...04 03416 ...
Page 611: ...08 05977 sheet 1 ...
Page 612: ...04 03428 ...
Page 613: ...08 05998 ...
Page 614: ...04 03429 ...
Page 615: ...08 06000 ...
Page 616: ...04 03415 ...
Page 617: ...08 05976 sheet 1 ...
Page 618: ...08 05976 sheet 2 ...
Page 619: ...04 03418 sheet 1 ...
Page 620: ...04 03418 sheet 2 ...
Page 621: ...08 05979 sheet 1 ...
Page 622: ...08 05979 sheet 2 ...
Page 623: ...04 03417 ...
Page 624: ...08 05978 sheet 1 ...
Page 625: ...08 05978 sheet 2 ...
Page 626: ...08 05978 sheet 3 ...
Page 627: ...04 03421 ...
Page 628: ...08 05984 ...
Page 629: ...04 03453 ...
Page 630: ...08 06067 sheet 1 ...
Page 631: ...08 06067 sheet 2 ...
Page 632: ...08 06102 sheet 1 ...
Page 633: ...08 06102 sheet 2 ...
Page 634: ...04 03377 ...
Page 635: ...08 05926 sheet 1 ...
Page 636: ...08 05926 sheet 2 ...
Page 637: ...04 03407 ...
Page 638: ...08 05927 sheet 1 ...
Page 639: ...08 05927 sheet 2 ...
Page 654: ...03 01079 ...
Page 700: ...04 03363 sheet 1 ...
Page 701: ...04 03363 sheet 2 ...
Page 702: ...08 05854 sheet 1 ...
Page 703: ...08 05854 sheet 2 ...
Page 704: ...08 05854 sheet 3 ...
Page 705: ...04 03364 ...
Page 706: ...08 05855 ...
Page 707: ...04 03370 ...
Page 708: ...08 05870 ...
Page 721: ...03 01080 ...
Page 749: ...04 03366 sheet 1 ...
Page 750: ...04 03366 sheet 2 ...
Page 751: ...08 05860 sheet 1 ...
Page 752: ...08 05860 sheet 2 ...
Page 753: ...04 03367 ...
Page 754: ...08 05861 ...
Page 771: ...03 01108 ...
Page 826: ...08 05994 sheet 1 ...
Page 827: ...08 05994 sheet 2 ...
Page 828: ...04 02541 ...
Page 829: ...08 03905 ...
Page 830: ...04 02690 ...
Page 831: ...08 03993 ...
Page 832: ...04 02691 ...
Page 833: ...08 05995 ...
Page 834: ...04 02852 ...
Page 835: ...08 04644 ...
Page 836: ...04 02487 ...
Page 837: ...08 03817 ...
Page 838: ...08 03995 ...