Peripheral Circuits - Alinco DX-SR9 T Service Manual

3) Peripheral Circuits

1. Beep and Sidetone Circuit
Sidetone is output by the STON line at pin No.24 of the CPU (MAIM UNIT) in
square wave. Beep is output by the beep line at pin No.16 of the CPU (MAIN
UNIT) in square wave. The sidetone frequency is switchable in the range of
400Hz to 1kHz. The VR1 is the volume control put which leads to the AP amp.
2. Tune Circuit
At the start of the tuning, the TUNE voltage comes out by which the one-shot
multi-vibrator operates and by the Q168 approximately 8V is output to
command the external auto tuner as a starting signal. Separately, an output
which goes low while tuning is created by the Q169 using the TUNE voltage.
When the starting signal is received by the external auto tuner (e.g. EDX-2),
the tuner outputs the said (low) output at TKEY terminal. The radio's CPU
monitors the TKEY terminal and while the voltage is at low level the radio is put
to the TUNE mode. If the TKEY terminal is low for more than 20 seconds, the
CPU releases the TUNE mode. During the TUNE mode the radio transmits in
AM mode besides microphone is muted and the carrier is suppressed at 10W
(adjustable).
3. Regulated Power Supply
The IC115 is a regulated power supply of 8V output. The voltage necessary for
transmission, namely T8V is created by the Q149, and for reception R8V by the
Q152. The IC117, Q151 and Q155 are Tx/Rx control. When PTT line is
grounded at the output of the Q161 by mic's PTT or CW keying, a High level is
output from the IC117:C, and buffered by the Q150 the output is sent to the
CPU in the front unit for Tx/Rx switching. The IC117:C, having delayed the
rising of reception with the R413, C408, and D158, controls Q149 with Q151.
When transmitting, the current flows from 13.8V thru the R410 and D156, and
since the Q149's base voltage is higher by one diode difference than 8V, the
emitter output will be just 8V. When transmitting, the Q151 is turned ON thus
the Q149's base voltage will be 0V, resulting no output on T8V line. When
receiving, the T8V line is shorted by the D157 to discharge remaining charges
in the capacitors on T8V line. The Q152 while receiving, similarly as T8V line,
has currents coming thru the D167 and R432 from the 13.8V line, and since the
base voltage of the Q152 is higher by one diode voltage than 8V, the base
voltage of the Q152 will be 0V hence no output on R8V line. When transmitting,
the R8V line is shorted by the D168 to discharge remaining charges in the
capacitors on R8V line. The input to the IC117:D, which goes low when
reception is started, is delayed with the R421 and C412, then inverted by the
IC117:B, followed by the Q155 to control R8V. If a voltage is applied to pin No.8
of IC117:C, the output at pin No.10 would vary with PTT going Low, hence a
PTT Lock is activated.
4. Mode Voltage Functions Control, BPF/LPF Switching
The CPU (MAIN UNIT) is controlling the mode voltage, preamp On/Off, Attenu-
ator, Power, BPF/LPF switching, AGC, break-in, and PTT-Lock. For each
mode, the Q167, Q170, Q171, Q177, Q179, Q181 and Q182 are turned on
providing 8V.
5. Low Pass Filter
The output from the final power amp goes through the low pass filter removing
the harmonics. The input/output for this filter is switched with a relay, and the
filters not used are shorted to ground thru relays. The LPF control utilizes the
control voltage for the BPF in the main unit. Each LPF is made of 5 pole Cheby-
shev filters, attenuating the second and higher order harmonics by more than
40dB.
L0
L1 2.5MHz~4.0MHz
L2 4.0MHz~7.5MHz
L3 7.5MHz~14.5MHz
L4 14.5MHz~21.5MHz
L5 21.5MHz~30.0MHz
The transmitting signal, having removed spurious contents by the LPF goes
thru the power detection circuit and
Tx/Rx switching relay.
6. Power Detection Circuit
The L901 is made by bifilar winding on a toroidal core in 10 turns. Hence the
two sides will have 20 turns with a center tap. When the jumper wire goes thru
the hole of the core, this itself is considered one turn having 1:20 transformer.
Since there are the R902 and R904 in parallel, it effectively means 50 ohm load
existing on both ends. For the jumper wire, it is equivalent to having 50Ω/
(20*20)=0.125Ω resistor existing in series. Hence when outputting 100W, the
voltage applied to ends of the said quasi-resistor is:
0.125/(50+0.125)*
Since the turn ratio is 20:1, the voltage between the L901 is [0.176*20=3.52V]
The center tap of the coil has the voltage a half of the above therefore the
current will flow reversely to that in the jumper wire. A voltage divided by the
TC901 and C904 is applied to the center tap, the voltage being in phase with
that in the jumper wire. If the voltage is adjusted with the TC901 to be equal to
the enter tap voltage, the R908 would have the voltages in phase adding each
other, and the R909 would have inverted phase canceling each other. If the
antenna impedance changes, there would be a differential voltage on the R909
without having cancellation due to phase or voltage difference hence having a
DC voltage after passing thru the D902. In this way, the voltage applied on the
R913 is proportional to the output power (forward voltage) and on the R914 is
to the reflected power (reflected voltage). Thus the output and reflected powers
are detected and in the main unit the power is controlled.
7. Power Switch
Pressing the SW1 turns the RL801 contact ON and 13.8V is supplied. At the
same time, the Q101 is turned on and 5V is supplied.
~2.5MHz BPF0, BPF1 1.8MHz band
BPF2 3.5MHz band
BPF3 7MHz band
BPF4, BPF5 10,14MHz band
BPF6 18,21MHz band
BPF7 24,28MHz band
(100*50) =0.176V