5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS
RT2048
5.5.
SELCALL UNIT (MODULE 5)
The input to the selcall is taken from the telephone output. The signal is first amplified and limited in U04/2 and then
it passes the bandpass filter. Finally the signal is rectified and compared with a reference level in the comparator
U04/1.
3.7125 MHz is divided in the programmable counter U06. The output of, this is divided by 2 and turned into a square
wave in the flip-flop U03/2. The outputs of the flip-flop is connected to the switches U02. The frequency, at which
the switches around the capacitors C03 and C04 are working, determines the resonance frequency of the filter.
Thus by changing the dividing figure to U06, it is possible to change the resonance frequency of the filter.
With R01 it is possible to fine adjust the resonance frequency of the filter (see the adjustment procedure).
Figure
f(nominal)
U06 input
U03 output
No.
(Hz)
14
13
12
11
6
5
4
3
(Hz)
1
1124
0
1
1
0
0
1
1
1
18022
2
1197
0
1
1
0
0
0
0
0
19336
3
1275
0
1
0
1
1
0
1
0
20625
4
1358
0
1
0
1
0
1
0
1
21838
5
1446
0
1
0
1
0
0
0
0
23203
6
1540
0
1
0
0
1
0
1
1
24750
7
1640
0
1
0
0
0
1
1
0
26518
8
1747
0
1
0
0
0
0
1
0
28125
9
1860
0
0
1
1
1
1
1
0
29940
0
1982
0
0
1
1
1
0
1
0
32004
R
2110
0
0
1
1
0
1
1
1
33750
When the radio is switched on the dividing figure, corresponding to the first figure in the selcall number, is shifted
out on port B0 on the uC at the interface unit which is connected to the input of U07. U07 is a serial to parallel shift
register which converts the signal to the dividing figure U06. If the correct tone is received the output of the
comparator U4/1 goes low. This output is connected to the uC’s SEL-DET. pin. When the tone disappears again
the uC will put out the dividing figure corresponding to the next figure in the selcall number.
If all five tones are received correctly, the port C06 (EXT. ALARM) on the uC goes high. This port is connected to
pin I on the connector to the option board at the RX/TX unit. At the same time the uC will send out an alarm tone
from D06 via the volume control and power amplifier to the loudspeaker. The alarm tone lasts for 10 secs after an
individual call, and after an all call it lasts until the selcall has been reset. If the SELCALL
T/R button is activated the alarm circuits and indicators are tested.
Page 5-18
Summary of Contents for RT2048 VHF
Page 1: ...INSTALLATION MANUAL SAILOR RT2048 VHF ...
Page 4: ......
Page 11: ...1 INTRODUCTION RT2048 Page 1 7 9403 BLOCK DIAGRAM ...
Page 12: ......
Page 22: ...2 INSTALLATION RT2048 Page 2 10 9346 626945 625473 ...
Page 24: ...2 INSTALLATION RT2048 2 8 REAR VIEW OF VHF RT2048 25567 9350 Page 2 11 ...
Page 26: ......
Page 31: ...3 Service RT2048 3 10 PIN CONFIGURATIONS Page 3 5 ...
Page 32: ...3 SERVICE RT2048 Page 3 6 ...
Page 33: ...3 Service RT2048 Page 3 7 ...
Page 34: ...3 SERVICE RT2048 Page 3 8 ...
Page 38: ...5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS RT2048 Page 5 2 ...
Page 89: ......
Page 90: ...Thrane Thrane A S info thrane com www thrane com M2048GB Issue E 0820 ...