Kenwood TR 851 A Service Manual

Page 2

TR-851A/E

CIRCUIT DESCRIPTION

MODEL NAME -
TR-SSIA (K. M) Tn-asI e (T, wl
UNIT NAME
FINAL UNIT X45-3030-l1 X45-3030-51
CAR UNlT xsoaowoo xso-aowoo
COMPOSITE UNIT (PLL, DRIVE, FRONT) XSO-BOSO-il xeo-aoso II
X5314w52lTl
NT u I xsa-Iaswz
CO "0'- T x53-14w621wl
COMPOSITE UNIT IRXI xso-iazo-m XGD-IBZDAOI
Table 1 TR-astA/E Pc board chm
D _ , Fr u. lMHzl VFO step lkHzl TX OFFSET Repeater Tone . .'
"""'°" N "W FM ssa DISPLAY shift (kill) mm
KTM 430,o~ 325:3; it: _ : :155 r7502): t
43939995 . - {a one we
w 12.5kHz 5kHz D-A o-e 1'5 I750 Tone

Table 2 Frequency configuration at destination

FREQUENCY CONFIGURATION

The TR-861A/E utilizes a PLL synthesizer system in-
corporating a digital VFO, which covers each band in
5,on steps. (See Fig. 1.)

Received signals are mixed with the first local oscillator
(388.585 to 398,585MH2) to produce the first intermediate
frequency of 41.415MH2. In 583 or CW, the receiver
operates as a double conversion system. The 10.695MHz
lF signal is mixed with the second local oscillator (30.72
MHz) to produce the second intermediate frequency of
10,695MH1. The 10,695MHZ IF signal is applied to crystal
filter XFI (L71-0249-05), and the signal is then applied

to the ring detector to obtain the audio output.
In FM, the receiver operates as a double conversion

system, The 10,695MHZ signal is mixed with the PLL re-
ference frequency of 10.24MH2 to produce the second
intermediate frequency of 455k H2.

The transmitter system operates as a double conversion
system. In 553 made, output from the carrier oscillator is
modulated by a balanced modulator to produce an inter-
mediate frequency signal, which is then mixed with the
first local oscillator signal to produce the two meter
transmit signal. The carrier oscillator circuit is controlled by
the microprocessor according to the selected mode.

During USB or CW receive, the carrier oscillator fre<
quency is 10.6935MH1. During LSB receive, it is 10.6965
MHzt During CW transmit, it is 10.6943MH1, ln FM. 3

10.695MHZ crystal oscillator frequency is Used that is
directly modulated and then mixed with the first local
oscillator signal.

To minimize internal heterodyne tones and spurs in the
frequency generator and analysis are controlled by a
microprocessor. The PLL-based frequency system consists
of two PLL synthesizer loops controlled by a 4vbit high-
speed microprocessor and a stable, analog RIT oscillator
circuit.

Flfin',

10.99sz

Within :20on at one
2.2kH2 or more at ads
Within 21 .5kHz at 20:15
Within :ZAkHz at 60dB
his or less

see or less

lurn
Nominal frequency
Allowable center trsq' deviation
Pass bandwidth and
attenuation handwldth
(based on minimum loss)
nipple
Minimum loss ,
Guaranteed attenuation was or more within mom:
I/o terminating impedance I.2kn:5%/50Ft5%

Table 3 Crystal filter 10F2.2$ (L71-0249-05) characteristic!
(Composit unit (RX) XF1)

Page 3

TR-851A/ E

CIRCUIT DESCRIPTION

imam:
:iosessunz
:mssssmm
105915MN1
:ioawwux

10555an
xFinxrrx commpnl

toassmuz

59st

146W

RECEIVER SYSTEM

0 General

Incoming signals lrorn the antenna pass through a low-
pass filter in the Transmitter Final unit and a diode swltih
(03,04) for transmit/receive selection. The signals then m
through antenna coil (L301) and then are amplified by 'a
GaAs FETs and junction FET (0301, 302i. Undesired
signals are removed from the RF signal by a Z-pole helical
resonators (L303,304) and the resulting signal is then
applied to the first mixer l0303l4 The signal is mixed there
with the first local oscillator signal from the PLL system
to produce the first IF signal of 41.415MHz. Undesirable
adjacent channel signals are removed from the first IF
signal by a monolithic crystal filter (MCF : XFI l.

The first IF signal is then distributed to either the $58
or FM circuits

In the SSS circuit, the first IF signal goes through noise
blanker gate (Di) then amplified by a Dual Gate MOS FET
(01) and then applied to the SSB crystal filter (XFI ). The
filtered signal is then amplified by the lst lF Amplifier
(02) and the 2nd IF Amplifier (03) and then applied to
the ring detector (05,06) to obtain received audio signals

ummm
20¢ Mixen MCF

430.0
«£0.sz

ANT sw

Fig. 1 Frequency configuration

In the FM circuit, the first IF signal is amplified by a
Grounded Gate (04) J-FET and applied to the second
mixer (05). The IF signal is mixed with 1024MHZ to pro-
duce the second IF signal of 455kHz, Adjacent channel
interference is removed from the second IF signals by FM
ceramic filter (CF1), the second lF signal is then amplified
and detected by IC2 to obtain the received audio signal

The audio signal from the $88 and FM circuits is then
amplified by a common audio preamplifier Ql (X59
1110-00). High-frequency components are removed from .
the audio signal by an active LPl= (02L The audio signal
is then applied to the audio volume control on the front
panel. The audio signal is amplified again by audio amplifier
ICZOI (030504 1) and then applied to the speaker.

Page 12

TR-851A/E

CIRCUIT DESCRIPTION

0 Mod. voltage twimhing and standby circuit

Fig. 11 shows the mode voltage switching and standby
circuit when a mode is selected with a front panel key,
the corresponding port on MPU-I is set to high (5V) and
an appropriate mode voltage is transmitted by switching
the 8V line.

When the PTT is pressed, MPU-II sends information to
MPU-I, and port P22 of MPU-l is set to H, swtching 04.
O Other I/O circuits
1. Busy input circuit

The Busy input circuit is used to determine whether the
scan or DCL system has received a signal, The squelch signal
from the receiver system is swuched by Q7 and applied
to port P10 of MPU-I. This signal also turns the BUSY
indicator on, using 06 and GB for switching.

I01
: uncms
EQUIVALENT cincunr

P 50
(L58)

2. Audio mute output (AL)

When checking memory channel M1, performing code
squelch during alert operations, port P41 of MPU-I is set
to H (5V) to mute audio output
3. Microphone "lull output (ME)

The ME signal is used to mute audio inputs from the
microphone when the DCL system transmits a control
signal, Port P53 oi MPU-Ill is set to H (5v) to switch 025
in the MIC input of the RX unit. This signal is also used tc
control a modern if: in the modern unit MU-i,

ICG
: orsAqu
EOUWALENT cincun 1

Lsa

p 54
(CW)

P 52
(USB)

I

IC

P 53
(FM)

MPU-I

Dz:
(ATX)

P2 2
5T8Yi

MAIN CHASSIS 06

(X534460-XXNA/6) lustr LED CONTROL

MPU-K
IC 301

- FIT-OmitNEL
; (X53-14so.xxl(B/6i

Fig. 11 MODE voltage switching and standby circuit

12