Alinco DX-70 User manual

DX-70
Service Manual
CONTENTS
• S P E C IF IC A T IO N S .................................................................................................................. 1
• C IR C U IT D E S C R IP T IO N ................................................................................................. 2
• S E M IC O N D U C T O R D A T A ........................................................................................... 1 2
• E X P L O D E D V I E W ................................................................................................................ 21
• P A R T S L IS T .................................................................................................................................. 2 8
• A D J U S T M E N T ............................................................................................................................. 4 2
• P C B O A R D V I E W .................................................................................................................... 4 9
• B L O C K D IA R A M ....................................................... . ....................................................... 5 8
• C IR C U IT D IA R A M ............................................................................................................... 5 9
• E D X - 1 ...................................................................................................................................................... 6 5
A L IN C O , IN C

SPECIFICATIONS
1) eneral
Operating mode J3E(LSB,USB). A IA (C W ). F3E(F )
Number of memory channels 100
Antenna impedance 50 Q unbalanced
Power requirement 13.8 V DC ± 15% (11.7 to 15.8 V DC)
Grounding method Negative ground
Current drain Receive 1.0 A max.
Transmit 20 A max,
Operating temperature -10 °C to +60 °C
Frequency stability ± 10 ppm (-10 “C to +50 °C)
Dimensions 178(w) X 58(h) X 228(d) mm
(179 X 71 X 268 mm for projections included)
Weight Approx. 2.7 kg
2) Transmitter
Transmit frequency
coverage
(e.g. U.S. Version)
160 m band
80 m band
40 m band
30 in band
20 m band
17 m band
15 m band
12 m band
10 m band
6 m band
1.8000 to 1.9999 Hz
3.5000 to 3.9999 Hz
7.0000 to 7.2999 Hz
10.1000 lo 10.1499 Hz
14.0000 to 14.3499 Hz
18.0680 to 18.1679 Hz
21.0000 to 21.4499 Hz
24.8900 to 24.9899 Hz
28.0000 to 29.6999 Hz
50.0000 to 53.9999 Hz
HF band
SSB. CW. F 100 W (high)
Approx. 10 W (low)
A 40 W (high)
j Power Approx. 4 W (low)
output
50 Hz
band
SSB, CW. F 10 W (high)
Approx. 1 W (low)
A 4 W (high)
Approx. 0.4 W (low)
odulation
system
SSB Balanced modulation
A Low power modulation
F Reactance modulation

Transmitter (continued)
Spurious emission HF bands Less than -50 dB (-45 dB in 10 Hz band)
50 Hz band Less than -60 dB
Carrier Suppression ore than 40 dB
Sideband suppression ore than 50 dB (at 1 kHz)
aximum F
deviation (default) HF bands ±2.5 kHz
50 Hz band ± 5 kHz
icrophone impedance 2 kfi
3) Receiver
Receiver circuitry Double conversion superheterodyne
Receive frequency range 0.1500 Hz to 30.0000 Hz. 50.0000 Hz to 54.0000 Hz
Intermediate frequency 71.75 Hz (1st) 455 kHz(2nd)
Sensitivity
SSB, CW
(S/N 10 dB)
0.5 to 1.8 Hz 0 dB (1 pV)
1.8 to 30 Hz -12 dB (0.25 (j.V)
50 to 54 Hz -16 dB (0.15 pV)
A (1 kHz,
30%, od,
S/N 10 dB)
0.5 to 1.8 Hz +20 dB (10n V )
1.8 to 30 Hz +6 dB (2 pV)
50 to 54 Hz +6 dB (2 |iV)
F (1 kHz.
3.5kHz, DEV,
S1NAD 12 dB)
28 to 30 Hz -6 dB|i(0.5 |aV)
50 to 54 Hz -10 dBji (0.3 }.iV)
Selectivity
SSB, A (Narrow) 2.4 kHz/-6 dB, 4.5 kHz/-60 dB
SSB(Nartow), CW(Standard) 1.0 kHzy-6 dB, 3.0 kHz/-60 dB
CW(Narrow) 500 Hzy-6 dB, 3.0 kHzA60 dB
A (Standard), F 9 kHz/-6 dB, 20 kHz/-50 dB
Superiors and image rejection ratio ore than 70 dB
Audio output power ore than 2.0 W (at 8 Q, 10% THD)
RIT/TXIT range ±1.4 kHz

ro
CIRCUIT ESCRIPTION
1. Receiver System
1) Filter Unit
a. HF Antenna Input SA501 and R527 are installed in the input part of HF antenna terminal as the
countermeasure against the thunder.
The electric charge of HF antenna is discharged at R527, and when the voltage
becomes over about 300V, the gap of SA501 is discharged so that the receiving
input circuit is protected.
The input signal from HF antenna is passed through the transmission/reception
selecting relay RL513. The followings are prevented in LPF consisting of 1525,
L526, C580, C581 and C582: 2m band image receiving, passing through the First
IF (71,75 Hz) and leaking of the first local oscillating frequency (72~130 Hz) to
the antenna terminal.
b. 50 Hz Antenna Input The receiving signal from the antenna of 50 Hz band is passed through the LPF
for transmission/reception and passed through the transmitting power detection
circuit, then led to transmission/reception switching circuit consisting of D508 and
D509, and to HPF. The signal is amplified about 8dB in Q503. Because the space
noise in 50 Hz band is less than it in HF band, its exclusive receiving preamplifier
is equipped to get high sensitivity.
The receiving signal of 50 Hz or HF is selected in RL514, then after passing
through the attenuator circuit (ON/OFF) of about 20dB consisting of RL515, R528
and R531 the signal is led to the ain unit.
2) Main Unit
a. Front End The receiving signal output from Filter Unit is fed to ain unit through CN2. •
HPF, consisting of L19, L20, C47, C48, C49, C50, C51 and C52, eliminates the
strong radio signal of W band of 1.6 Hz or below. In case of receiving the
signal of 1.6 Hz or below, the sensitivity is controlled by the attenuator in R37 and
BPF1, also the signal is separated into 1.6 Hz, over or below.
5 BPF units consists of 9 filters. Each filter covers the following frequency range.
The frequency of 2.5 Hz or more consists of Chebyshev BPF, and under 2.5 Hz
frequency band is LPF. Two BPF's are installed on the same unit. Not to be
influenced so much, the distant frequency band BPF’s are combined.
-1.6 Hz BPF1
1.G - 2..5 H2 BPF2 1.8 Hz
2.5 - 4.5 Hz BPF3 3.5 Hz
4.5 - 7.5 Hz BPF4 7 Hz
7.5 - 10.5 Hz BPF1 10 Hz
10.5- 14.5 Hz BPF2 14 Hz
14.5- 21.5 Hz BPF3 18, 21 Hz
21.5- 30 Hz BPF4 24, 2B Hz
50 - 54 Hz BPF5 50 Hz

Passing through BPF, the signal turns ON/OFF in the switching diode, D29 and
D30. This preamplifier is the parallel grounded gate operation of Q9 and Q10
(2SK2171), so the unit can obtain a good performance at a high level input signal
with low NF.
The wide range frequency from about 1 Hz to 60 Hz is amplified about 10dB.
This lOdB preamplifier and 20dB attenuator in the Filter unit are combined, then by
pressing RF gain switch on the front panel, one of four steps, -20, -10, 0, or +10dB
is selected.
The LPF, consisting of L52, L53, L54, C103, C104, C105, and C106, prevents the
following first receiving mixer from the local oscillation leaking, and also prevents
the first IF and image of the spurious receiving.
The first receiving mixer consisting of Q10 and Q11 is the balanced mixer, in which
the local oscillating signal is fed to the gate of 2SK2171.
7 he 3rd intercept point is about 20dBm, and local oscillator of about 2V P-P is fed
to the gate. The receiving signal is converted into the first IF of 71.75 Hz.
As the ratio of the spurious interference is decreased in 50 Hz band mode, the
trap of 71.75 Hz consisting of L72 and C107 keeps the ratio of spurious interfer
ence 70dB or more in all band.
b. The First IF Amplifier Circuit FL1: A and FL1: B are the crystal filters of 71.75 Hz. By the combination of two
filters, the unit has the characteristics of the band width of 15kHz or more/3dB and
the value of guaranteed attenuation of 70dB or more. Here the image ratio is
determined 70dB or more (approx. 80dB}. The first IF amplifier circuit of Q12 is
located between the crystal filters to prevent the loss in the front-end and mutual
interference.
The first IF amplifier circuit Q12 decides the sensitivity after passing the mixer.
AGC voltage is applied to the second gate.
c. The Second ixer Circuit, The Second Amplifier Circuit
DB (Double Balanced ixer) consists of L14, D7 and L16. The signal is passed
in the opposite direction while receiving or transmitting in this DB . Approximately
OdBm is as the second \ocat oscitaVing \evel, and the third IP is approximately
lOdBm.
The receiving signal (71.75 Hz) and the second local oscillating frequency
(71,295 Hz) is mixed, and unwanted signal is eliminated in LPF consisting of L17,
L73 and C36, then the signal of 455kHz is generated. After passing through the
switching diode D8, the signal is amplified in Q22. The source of Q22 is controlled
by the output of the noise blanker circuit.
d. IF Filter
After passing through the transmission/reception switching diode D9, the signal is
led to one oi three ceramic filters of 455kHz. The selectivity is decided here
except CW narrow.
SSB, A -NARROW FL3(CFJ455K5) 2.4kHz/-6dB 4.5kHz/-60dB
SSB-NARROW, CW FL2(CFJ455K8) 1.0kHz/-6dB 3.0kHz/-60dB
F , A FL.4(CFW455G) 9kHz/-6dB 20kHz/-50dB
Each filter has 4 switching diodes (D3-D48) in front and rear to isolate the filter.

The isolation is required the value of guaranteed attenuation of each filter (approx.
70dB) or more. The diode connected in parallel in front and rear of no used filter is
short and the diode connected in series is open. The combination of open and
short is used to get the high isolation.
The modes, transmission/reception and wide/narrow of this filter are selected by
Q36-Q46, D79, D80, D82, D83, D84.
e. The Second IF Amplifier Circuit
f. Demodulation Circuit
g. CW Audio Filter
After passing through the filter, the signal is led to the transmission/reception
switching diode D49, and amplified in Q23 and Q24, then buffered in Q25.
The AGC voltage is applied to the second gate of Q22, Q23 and Q24.
The output level of 025 is fixed because the AGC voltage is added to the receiv
ing signal.
This output signal is used for the demodulation in SSB, A and CW modes and
AGC detection.
In the F mode, after passing through the transmission/reception switching diode
of D49, a part of receiving signal is fed to 1C7( C3357) from C221, then it is IF-
amplified and demodulated. C214 is connected in parallel to the feedback resister
R182, and the resister is de-emphasized. Even in the F mode, Q23, Q24 and
Q25 are active, also AGC is operated.
In SSB and CW modes, the following local oscillating frequency is supplied from
PLL unit to IC3 balanced mixer, then the signal is demodulated.
The receiving signal is fed to Pint, and local oscillation Pin3, then picked up the
demodulation output of approximately 100mV from Pin7.
USB 456.5kHz +IF SHIFT
LSB 453.5kHz +IF SHIFT
CWU 455.8kHz +1F SHIFT
CWL 454.2kHz +IF SHIFT
The output is led to the switching circuit of each mode, and to the CW audio filter.
In A mode, the signal is detected in D51, then led to IC5.
In F mode, the signal is demodulated and de-emphasized in above-mentioned
IC7, then led to IC5.
IC4 is the active filter, which consists of the combination of low-pass filter and high-
pass filter in the operational amplifier. It has the band width of about 600Hz (-6dB)
centering the trequency of about 800Hz.
h. AF, AGC Time Constant Selection
1C5 is the analogue multiplexer which has 2 circuits with 4 contact points, and
switches the demodulation output in every mode and AGC time constant. The
voltage combined in D55 and D56 is input to Pin9 and Pinl 0, then the output of
1C3 (SSB, CW-W), the modulation output of F /A and CW audio filter output
(CW-N) are selected. The voltage of 8V is applied to Pin6 (INHIBIT) when
transmitting, and the modulation output is turned OFF unconditionally.
GO

i. AF Amplifier
The voltage that can pass through the analogue switch of IC5 is very low. The
voltage is amplified approximately 20dB in IC12: B to get higher AF input voltage
to following IC13 (voltage controlled electronic volume). Also a part of this output
is picked up and output to Pin6 of microphone as non-squelched audio output.
This output is used as the terminal of packet, RTTY, SSTV, etc.
j. Electronic Volume, AF Amplifier
IC13 is the dual electronic volume controlled by the voltage.
The volume is controlled by the AF GAIN VR on the front panel. Pin5 is the control
terminal. The value of the attenuation is the minimum when the control voltage is
about 3.4V, and the value is 90dB or more at maximum when the control voltage is
about 3.1V.
One of the circuits is for volume control of the demodulation sound, and the other
for the volume control of the beep and sidetone. The beep and sidetone can be
heard even if the volume is set to the minimum point and sound tone is related with
AF GAIN VR.
The squelch circuit (IC14:A, Q14) controls Pin5. The output of IC14: A activates to
close the squelch when transmitting, so Q14 is turned OFF in D85 to control the
volume of the sidetone.
The receiving sound is fed to Pin6 and applied from Pin7. As for the beep and
side tones, Pin2 is for input and Pin 1 for output. These two outputs are combined
with the inpul of LPF amplifier IC12:A. The high tone noise that is generated in IF
amplifier is decreased by LPF amplifier.
The output of IC12: A is attenuated in R309 and R310 to get the same level with
IC20, and also to decrease the noise. IC20 is the AF power ampliiier which can
get the output of 2W or more (THD 10%) at 8£2 load. The ripple filter consists of
Q51 and C260.
The AGC voltage is supplied one stage to first IF amplifier and three stages to
second IF amplifier. These IF amplifiers consist of 3SK131. AGC voltage is
applied to the Gate2. The IF amplifiers are designed that the gain is changed
linearly corresponding to the AGC voltage.
D53 and D54 are the rectifier, and Q26 is DC amplifier. D50, the anode is set to
about 2V in R176, D110, D111 and R177. Usually AGC voltage is applied 2.4V.
The strong signal rectifies D53 and D54 resulting in DC voltage. Q26 decreases
the AGC voltage.
When AGC-FAST is selected in SSB/CW mode, C205 and C206 are connected
between 5V and AGC line in parallel. The attack time of AGC is determined in
R167 and C206, then the release time is determined in R168 and C206. The
characteristics are "fast attack" and "slow release". In case of AGC-SLOW, the
analogue switch IC6 is turned ON, then R175 and C287 are connected in parallel.
The release time is lengthened because of C287. In case of A , C206 is con
nected in parallel, then the attack time is delayed, which is the average type. D110
and D111 is the thermal compensation of D50.
in receiving A , AGC is the average type not to follow the modulation.

I. S eter, Squelch
The output of Pin 1 and RF meter output are combined in the diode, then it is sent
to the front CPU to display the meter. The output signal of Pin1 is fed to Pin6 of
IC14:A. The voltage of Pin5 is determined by the squelch VR of front unit. Com
paring with this voltage, the squelch is opened or closed.
While the check operation the CPU output decreases the voltage of squelch VR in
front side to open the squelch forcedly. The squelch output controls IC13, at the
same time it is provided to the front unit to light RX LED and led to CPU unit.
m. Noise Blanker Circuit
This circuit eliminates the pulse noise of a car, etc. Because the noise emitting
time is short, in this duration the operation of receiver is stopped to prevent the unit
Irom emitting a noise. The pulse noise is delayed when it is passed through the
narrow band filter, and the emitting time becomes longer. It makes difficult to
eliminate the noise, so it is necessary to eliminate the noise in the earlier stage.
A part of the second mixer output, whose band width is limited, is amplified in Q20,
Q19, 018, and Q16. The signal is detected in D33 and D34, and the AGC voltage
is applied to 019, Q18 and Q16.
The charge time constant of this AGC is determined by R82 and C128, and also
the discharge constant is determined by R81+R82, C128. The voltage of AGC
does not rise suddenly because of the charge constant, so that this voltage is not
applied to almost all the short signals such as pulse noise, but is applied to the
continuous signals such as receiving signal and amplilier gain is decreased.
While emitting the pulse noise, the AGC voltage does not follow the pulse noise,
so the detected voltage is high, then 015 is turned ON in that time.
On the contrary, as for the continuous signal, the detected voltage of D33 and D34
is fixed by AGC, so 015 is turned OFF because of the emitter bias of R85 and
R84.
Namely Q15 is turned ON only the time of the pulse noise, then 021 is turned
OFF. The source of IF amplifier of 022 is biased through R98 and R102 so that
the gain is decreased and the signal is blanked. When the emitter of Q15 is
biased to high, the Noise Blanker is turned OFF.

2. Transmitter System
1) Main Unit
a. icrophone Amplifier The input signal from microphone is amplified by the low noise amplifier 056
through the mic gain VR1. It is possible to bias (8V) the microphone terminal with
R388 for the microphone which needs the power supply, (solder bridge)
In SSB/A mode, The gain of IC21 (approx. 15dB) is determined by R329 and
R328.
In F mode, R330 is connected to R320 in parallel by Q55, then the gain is
increased approximately 34dB. Also the cut off frequency is risen, and the signal
is pre-emphasized and operated as a limitter.
In the SSB/A mode, C345 and R384 are conntected to the feedback circuit by
Q63 when the speech compressor is turned ON. The gain is increased about
15dB, then IC21:B is operated as the limitter.
When the speech compressor is ON, the low frequency is cut by C345.
In F mode, the gain is risen enough, so the speech compressor has no effect.
The output of Pin1 of IC21: B is attenuated in R326 and R325. The subaudible
tone from PLL unit is applied through R325. (When the Tone is ON.)
IC21: A is LPF amplifier that is the Splutter filter in F mode, and it is operated for
speech compressor.
This signal is output to PLL unit as the F modulation, and output to the balanced
modulation of IC2.
The output to IC2 is muted by Q54 in CW/F mode.
b. Balanced ixer !C2 is the balanced mixer, and the carrier is suppressed in SSB mode. To get
more ratio of carrier suppression, the balance adjustment of VR3 and VR4 are
applied.
The carrier is necessary in CW/F /A mode, so the input of Pinl is made unbal
anced by applying the DC voltage to obtain the carrier.
By applying the DC in A /F mode, or by keying in CW mode, the balance is
broken to obtain the carrier wave. VR11 is used for the adjustment of carrier level.
In the A mode, the DC and modulation is added simultaneously. In SSB mode,
the modulation is added by R317. In A mode, D93 is DC-biased and turned ON.
Then the attenuator consisting of R317 and R393 limits the modulation.
c. IF Filter After the output of !C2 increases the impedance in C177 and L77, it is passed
through D49 and led into band limit IF filter. D52 is isolated highly by connecting to
the output in parallel at receiving. In SSB mode, the output is DSB signal. (Double
Side Band)
The filter is switched by the selection of above-mentioned diode switch. The signal
is passed through the following filer in each mode.
SSB FL3(CFJ455K5) 2.4kHz/-6dB 4.5kHz/-60dB
CW FL2 (CFJ455K8) 1.0kHz/-6dB 3.0kHz/-60dB
F , A FL4 (CFW455G) 9kHz/-6dB 20kHz/-50dB
SSB is obtained by eliminati'ng one of side bands of DSB through the filter.

d. IF Amplifier, The Second ixer
After passing through the filter, the signal is led to D37, Q7, and D6, and passed
through the second mixer in the opposite direction of the receiving, then the signal
of 71.75 Hz is obtained. Q6 operates the CW keying.
The voltage of ALC is added to the second gate of Q7.
The local oscillating signal of 71.295 Hz and unwanted signal are eliminated in
FL1: A and FL5. The signal is amplified in 05, passed through FL5, then led to the
balanced mixer of Q3 and Q4.
e. The First Transmitting ixer
This mixer is the balanced type, and the unwanted signals (IF and local oscillating
signal) are decreased. The best operation is selected by biasing the second gate.
To decrease the spurious, the signal is balanced in VR1.
f. Power Amplifier Passing through tihe mixer, the transmitting signal which has the desired transmit
ting Irequency is passed after switching the LPF tor HF band or BPF tor 50 Hz
band. The unwanted signal and especially the leak of local oscillating signal is
decreased as less as possible.
The signal is amplified up to 0~3dBm in Q1. T notch filter consists of C1, C2 and
11. It is tuned to approximately 44 Hz while using 50 Hz band to decrease the
spurious signal. Then the signal is supplied to PA unit.
2) PA Unit
a. Power Amplifier
The signal input to PA unit is amplified up to approximately 100mW. The idling
current of 0601 flows about 100mA during transmitting as A-class amplifier. The
frequency characteristics are compensated by feedback, besides connecting the
capacitor to emitter resistor in parallel.
The signal is amplified up to 10W in Q602 and Q603.
PA amplifier is the wide band range from 1.8 Hz to 50 Hz
The idling current flows 100mA (adjusted in VR601), and the amplifier is the push-
pull type.
D601 is connected to Q602 and Q603 thermally, and the idling current is compen
sated for temperature. This output is switched at RL601 in 50 Hz, then supplied
to filter unit.
b. Final Stage Power Amplifier in the final stage amplifier circuit consisting of Q604 and Q605 (2SC2904), the
idling current of about 300mA is flowing. The base bias is made by Q606. D604
and D605 are connected to 0604, 0605 and Q606 thermally, and the idling current
is compensated for temperature.
The feedback circuit, consisting of R621, R622, R623, C633, R627, R628 and
C637, makes the gain flat in the wide range of 1.8 Hz~30 Hz.
The 100W output is led to filter unit.
The collector cun'ent of 0606 and Q607 is detected by using FB606 and L611.
Then led to the main unit.
U l