User Manual

CIRCUIT ANALYSIS

Test Point TP31 by connecting the negative lead to TP31 and the positive lead to ground

(TP32 or TP33).

6.5.4High-Speed Data Transmit Filters

Buffer/follower circuit U6A precludes the quad operational amplifier high-speed data

transmit filter circuits for RFTXDAT. The output of this circuit can be monitored at TP1.

The output of U6A is applied to the inputs of high-speed Data Transmit Filters:

• 9600 Baud Wide Band

• 4800 Baud Narrow Band

• 9600 Baud Wide Band ETSI

• 4800 Baud Narrow Band ETSI

• 9600 Baud Narrow Band Switched Capacitor Filter Circuit

The High Speed Data (HSD) filter is an active Gaussian Minimum Shift Keying

(GMSK) filter that filters the data transitions to minimize the high-speed-data

transmission bandwidth. The frequency response of the HSD filter section is changed by

selecting the output of only one filter circuit by 8:1 MUX U7.

High-speed data is a 4800 or 9600 bit per second data stream generated by the

microcomputer through the RF data modem U9 on the Modem Daughter Board.

Each of the HSD filter circuits has two sections.

6.5.4.1 9600 Baud Wide Band

This HSD filter circuit consists of operational amplifier U5B followed by operational

amplifier U5A. The output of U5A, Pin 1 is applied to the input of 8:1 MUX U7, Pin 4

(N01). This HSD amplifier filter output can be monitored at TP4.

6.4.4.2 4800 Baud Narrow Band

This HSD filter circuit consists of operational amplifier U5C followed by operational

amplifier U5D. The output of U5D, Pin 14 is applied to the input of 8:1 MUX U7, Pin 5

(N02). This HSD amplifier filter output can be monitored at TP5.

6.4.4.3 9600 Baud Wide Band ETSI

This HSD filter circuit consists of operational amplifier U10B followed by operational

amplifier U10A. The output of U10A, Pin 1 is applied to the input of 8:1 MUX U7, Pin 6

(N03). This HSD amplifier filter output can be monitored at TP6.

6.4.4 4800 Baud Narrow Band ETSI

This HSD filter circuit consists of operational amplifier U510C followed by operational

amplifier U10D. The output of U10D, Pin 14 is applied to the input of 8:1 MUX U7, Pin

7 (N04). This HSD amplifier filter output can be monitored at TP7.

European Technical Standards Institute

MM101271V1 R1A 51