Sailor RT2047 Service Manual download pdf (Page 52)

2 CIRCUIT DESCRIPTION RT2047 DSC - PART II

2.6.7 PA REGULATOR

By means of the PA regulator it is possible to adjust the output power of the transmitter. When the output

from U3/2-6 is changed from O to 5V, Q7-6 is turned off. Thus Q8-6 is turned on and then also Q2-6 and

Q1-6 and the output voltage rises. When the voltage at the base of Q8-6 is equal to the voltage on the

base of Q7-6 the current in Q8-6 is reduced and then also in Q2-6 and Q1-6 and the output voltage

stabilises. The output power from the TX POWER AMPLIFIER is adjusted by changing the output voltage

of the PA REGULATOR with R68-6. When reduced output power is chosen (0W mode) the µC turns PB5

to 0 V and the reference voltage to the regulator will be lowered. It can be adjusted at R29-6, and thus

also the reduced output power.

2.6.8 RX FILTER CONTROL AMPLIFIER

The control voltage from the RX VCO is turned into a control voltage to the capacity diodes in the band

pass filters in the receiver.

2.6.9 MICROPHONE AMPLIFIER

The amplifier consists of three stages. In the first stage the signal is preemphasized. In the next stage

the signal is clipped when the input signal is big enough, and in the last stage the signal is deemphasize

before it is led to the modulator in the TX EXCITER. The deemphasizing is necessary because it is a phase

modulator.

2.6.10 SQUELCH CIRCUIT

The signal from the receiver is fed to the active high pass filter U5/1-6. The filter attenuates signals below

10 KHz which means that talk will not be detected. The output of the filter is fed to the clipper Q15-6 and

the detector comprising the capacitor C45-6, the diodes D13-6, D14-6, and the resistors R3/1-6 and R5/

1-6. The rectified noise level is compared with a reference level in the voltage comparator U15/2-6. When

the noise level is higher than the reference level, the output will be low. This output is connected to PD7

on the µC, which will turn off the AF by means of U18-6, except if the squelch setting is 0 ( in the display),

The correspondence between the number in the display and the latch U4-6 can be seen below:

64 :LWKRXWFDUULHU :LWKFDUULHU

%%%% %%%%

0 1 1 1 1 1 1 1 1

1 1 1 1 0 1 1 1 1

2 1 1 0 1 1 1 1 0

3 1 1 0 0 1 1 0 1

4 1 0 1 0 1 1 0 0

5 1 0 0 0 1 0 1 0

6 0 1 1 0 1 0 0 0

7 0 1 0 0 0 1 1 0

8 0 0 1 0 0 1 0 0

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Sailor RT2047 Service Manual Page 52