Circuit Description; 0-1. Frequency Configuration; 0-2. Local Oscillator Pll Circuit - Kenwood TS-940S Instruction Manual

10. CIRCUIT DESCRIPTION
10-1. FREQUENCY CONFIGURATION
The TS-940 is quadruple conversion in SSB, CW, AM and FSK modes and triple conversion in FM mode. As a trans-
mitter, it is double conversion in CW and FM modes and triple conversion in SSB, AM and FSK modes.
Fig. 1 0-1 shows the frequency configuration of the signal paths as both a transmitter and a receiver.
30KHz
-30MHz
X
1-
Qg(RFl (IF) 04.5(1 Fl
RX MIX1 45.05MHz RX MIX2
VC03
45.08
I
75.05MHz
HET CARO
8830MHz
SSB
AM
8830KHz
Q7.1!1Fl
1CAK2
CAR 2
9285KHz
+
455KHz
455KHz
CARl
1455KHz)
"
V>
LL
OISCRI
r...____,IC>
RX
OUT PUT
~----<D-C~s=ss=--,_--<K MIC INPUT
AM
TX MIX3 45.05MHz TX MIX2 FSK TX MIXl
0
8
73
"M( IF)
044,45IIF)
Ot,2(RFJ IRF-IF) Qso,st!IF),L_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ----'
Fig.
10-1
10-2. LOCAL OSCILLATOR PLL CIRCUIT
This is a digital VFO (Variable Frequency Oscillator) that
covers a frequency range of 45.08 MHz - 75.05 MHz in
1OHz steps. Three PLL loops are linked in analog mode.
The dividing ratio data to each PLL is controlled by the mi-
croprocessor.
Each loop is of a single crystal frequency control sys-
tem: the VCO phase is compared with the unique refer-
ence frequency STD . CAR1 and CAR2 frequencies are in-
serted halfway in the analog link, enabling variable band-
width functions such as VBT and slope tuning.
The PLL circuit is shown in Fig. 1 0-2.
10-3. RECEIVER
The signal from the antenna is applied to the RF unit
(X44-1 660-00) ANT terminal. The signal passes through
the transmitter/receiver selector circuit and out the EXT
terminal. The output is connected to the RF unit RXA ter-
minal via the selector circuit provided on the rear panel.
This signal is applied to the receiver BPF through the RF
attenuator (0, 1 0, 20, or 30dB selectable) via relays RL 1
and RL2. The BPF divides the received frequency range
into nine bands, which are automatically selected by RX
BPF control data (ABO - RB3) from the Digital unit A
(X54-1830-00).
The signal from the BPF is passed through the RF AGC cir-
cuit composed of PIN diodes D23 and D26. It is then am-
plified by RF amplifier 01 0 and applied to the first re-
ceiver mixer 09, where it is mixed with the VCO signal to
become the first IF signal at 45.05 MHz. This signal is ap-
plied to grounded gate amplifiers 07 and 8, and the out-
put is applied from the RIF terminal to IF unit
(X48-1430-00).
The unwanted signal components are removed from the
45.05 MHz first IF signal by 15 kHz MCF XF1. The signal
is then applied to the second receiver mixers 04 and
05, mixed with the (36.22 MHz) HET signal and converted
to the (8.83 MHz) second IF signal. This signal is separ-
ated into two channels: one is supplied to the noise
blanker on the Control unit (X53-1420-XX), and the other
is applied to the second IF filter via noise blanking gate D3
-06.
This filter circuit is provided with crystal filter
XF2: YK88S1 with a 2.7 kHz bandwidth for SSB (used
also for wide CW /FSK and narrow AM), and wide band LC
filters L37, L38 for FM (used also for wide AM when the
optional AM filter is not provided.) As an option, the filter
circuit permits use of two filters: a YK-88C-1 with 500Hz
bandwidth for CW and a YK-88A-1 with 6kHz bandwidth
for AM. These four filters are automatically selected by
the W/N-mode information (WN, ND2 and MD1) from Di-
47