Kenwood TM-D700A Service Manual

TM-D700A/E
CIRCUIT DESCRIPTION
7. Data Terminal and Peripheral Circuits
J700 (data terminal) is the data communications terminal on
the front. It handles transmission control, data input/output, and
squelch signals.
There are two data communications modes: 9600bps mode
and 1200bps mode. 9600bps mode communications are
FAST FM mode of SSTV, GMSK and G3RUH packet
communications. Unlike with 1200bps AFSK, with this type of
high-speed modulation, frequency modulation is carried out
after the digital base band signals (rectangular wave) are
passed through a band limiting filter. For 9600bps GMSK for
example, compared to 4800Hz signals (nearly sine wave
signals passed through a filter), these signals have a hissing
sound like digital modulation when listened to by ear. Different
7-1. Transmission signals
Transmission modulation signals enter from PKD of the
data terminals (J700). The path to the modulation depends on
whether communications are 1200bps or 9600bps mode.
For 1200bps mode, the transmission modulation signals
pass through the analog switch (IC803), and are input to 1C801
(Pin 6). The signals pass through the pre-emphasis (Q801,
Q802), are adjusted.by the electronic volume, and are input to
the VCO.
types of modulation, such as GMSK and G3RUH, are
distinguished by the type of band limiting filter.
fin meine Specification
bps switching 1200bps 9600bps
1 PKD 'Modulation input 40mVp-p 2Vp-p
Frequency shift 3+0.5kKHz 2.2+0.5kHz
Output level 500mVp-p/10kQ
4 PR9 : :
Always output during reception
5 PRI Output level 500mVp-p/10kQ
Not output when squelch off
Table8 DATA terminal input/output level
For
9600bps
mode,
the
transmission
modulation
signals
pass
through
IC803
and
amplified
by the
tone
amp
(IC802).
Then
it
is
adjusted
by
the
electronic
volume,
and
are
input
to
the
VCO.
The
frequency
shift
depends
on
the
input
signal
level,
so
there
is
an
amplitude
limiting
circuit
(D702,
D703)
to
hold
the
signal
below
4
Vp-p
to
avoid
extreme
shifts.
Thanks
to
this
circuit,
the
PKD
signal
does
not
go
above
4
Vp-
Pp
and
the
frequency
shift
does
not
fluctuate
extremely.
ANALOG SW
IC 803
eats
PKD © C
Sac o-~<f- COMPUTER
PRI O~
PRI O
PKS oe eeicie
IC703
BUFFER
aes
AMP IC801
BUFFER
IC 802
TA75SOIF
ELECTRONIC
VOLUME
IC804
PRE-EMPHASIS vco
Q801 Q802 Z
2804617 28C4617 H———-> VCO
(S) (S)
Fig.18 Transmission signals
15

Kenwood TM-D700A Specifications

General

Brand	Kenwood
Model	TM-D700A
Category	Transceiver
Language	English