RF Technology R150 Instruções de Operação descarregar pdf (Página 14)

Page 14 RF Technology T70/T150

5.7 Local Microphone Input 5 CIRCUIT DESCRIPTION

The bridge configuration allows audio signal inversion by interchanging the positive

and negative inputs and minimizes ground loop problems. Both inputs should be

connected, with one lead going to the source output pin and the other connected to the

source audio ground.

5.7 Local Microphone Input

The local microphone input is provided for use with a standard low impedance

dynamic microphone. The microphone output is amplified by U9a before connecting

to analog switch U10a. U10b inverts the local microphone PTT input to switch U10a

ON when the microphone PTT button is pressed. U10a is OFF at all other times.

The local microphone audio has priority over the other inputs. Activation of the local

microphone PTT input switches OFF the audio from the line or direct inputs through

D16 and U10c.

5.8 CTCSS and Tone Filter

The CTCSS encoder module H1, under control of the main microprocessor U13, can

encode all 38 EIA tones and (on some models) additional commonly-used tones.

The tone output of H1 connects to jumper JP8 which is used to select either H1 or an

external tone source. The selected source is coupled to U9c which is a balanced input

unity gain amplifier. The buffered tone from U9c is fed to a 300 Hz low pass filter

U7c.

On Rev 4 or later revisions, the low pass filter can be bypassed by inserting a jumper

onto JP17.

RV3, the tone deviation trimmer, is used to adjust the level of the tone from U7c

before it is combined with the voice audio signal in the summing amplifier U7a.

Back to back diodes D4 and D5 limit the maximum tone signal amplitude to prevent

excessive tone deviation when external tone sources are used.

The subtone amplifier, filter and limiter can be bypassed on Rev 4 or later exciters by

removing the link from JP22 and moving the link in JP16 to the alternate position.

5.9 Audio Signal Processing

Jumper JP4 selects either the line or direct input source. The selected source is then

connected to JP6. JP6 can be removed to provide 20 dB attenuation when the input

level is above 10 dBm to expand the useful range of the line level trimmer RV4. The

wiper of RV4 is coupled to the input of the input amplifier U9d. U9d provides a

voltage gain of ten before connecting to the input of analog switch U10c.

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RF Technology R150 Instruções de Operação Página 14