Voice Band Inverter

4

MX014

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2. Signal List

Pin No.

Name

Description

1

XTAL

An external 4MHz clock can be applied to this input. The clock circuit on chip has a resistor

and capacitors so that only one external crystal is required.

2

XTAL

This is the inverted 4MHz clock output for use when a crystal oscillator is used, or as a buffer

for driving other clocked devices.

3PTT

Push To Talk is an input with a 3M

Ω pull-down resistor.

4

PTT

This is the inverted PTT output. It has a 100k

Ω output impedance.

5PTL

Push To Listen is an input with a 3M

Ω pull-down resistor.

6

PTL

Push To Listen is the inverted output of PTL; it has a 100k

Ω output impedance.

7

RXAUDEN

RX Audio Enable is an input with a 3M

Ω pull-down resistor.

8

RXAUDEN

RX Audio Enable is the inverted output of RX Audio Enable; it has a 100k

Ω output impedance.

9

PRIVEN

Privacy Enable controls the input action of the balanced modulator by switching the carrier

clock. When audio signals are inverted, the signal path gain is adjusted automatically to

compensate for the upper sideband loss. It contains a 3M

Ω pull-down resistor.

10

RXOUT

11

TXOUT

12

The negative supply pin (ground).

13

BPFOUT

For a gain of one in the RX Output stage, these two pins are wire linked together. However,

14

RXBIN

if gain is introduced at the RX input, attenuation may be introduced at the RX Output using

these pins and two resistors.

15

DEMPOUT

The pre-emphasis circuit has a 10dB gain at 1 kHz. Additional gain, or attenuation can

16

TXBIN

be introduced as in the RX path.

17

BIAS

18

FILTR

This filter is the output of the Input Audio BPF and must be a.c. coupled into the Balanced

Modulator Input through a 0.1µF capacitor.

19

BALMOD

This is the input to the balanced modulator. It must be a.c. coupled to the Filter Output.

20

RXIN

This is a negative input of an op-amp at the input of the RX path. It can be used, along with

RX Audio Feedback and two external resistors, to increase the signal to its optimum level prior

to frequency inversion/filtering. This may improve the S/N.

21

RXFB

RX Audio Feedback is the output of an op-amp at the input of the RX path. See RXIN.

22

TXIN

The negative input of an op-amp at the input of the TX path. It can be used, along with TX

Audio Feedback and two external resistors, to increase the signal to its optimum level prior to

frequency inversion/filtering. This may improve S/N.

23

TXFB

TX Audio Feedback is the output of an op-amp at the input of the TX path. See TXIN.

24

The positive supply pin.

Table 1: Signal List