Circuit Description - Kenwood TM-201A Service Manual

M-201A
CIRCUIT DESCRIPTION
RX SECTION
"ne input signal from the antenna passes shrough
E receiver dicde switch on the Final unit before
aaing .nput te the front end. The front end is comprised of
ampifier Q1 (GaAs FET 3SK97 2), first mixer C2
25K74L), a 3-pole helical resonator having a 4 MHz band-
cass and a 2-stage MCF (Monolithic crystal filter) to give good
Jassitivity and two signal characteristics.
The first IF signal (10.695 MHz), having passed through the
's mixed with the (10.240 MHz) second local oscillator
s.gnal at the second mixer Q3 (3SK74GA) to produce a se-
cond IF signal at 455 kHz. This (455 kHz) second IF signal is
assed through ceramic filter CFW-455F, IF amplified hy 04
A7302P), Q5 (2SC2668Y], and Q6 (4PCS77HI and
.cted by ceramic discriminator CFY-455S. The (10.240
M2) second local oscillator output is also used by the
iver PLL for the comparator reference signal
Tne detected output from the discriminator is divided into an
audio frequency component and a noise component and are
'ren coupled into their respective circuits. The audio frequen-
2/ component is de-emphasised, and preamplified by Q7
2SC2458Y) before delivery to Q14 (M83712), which the
ower amplifier which drives the speaker. The noise compo-
nant is derived through the BPF (bandpass filter), which
32tects the noise in the vicinity of 20 kHz. This is amplified by
8 and Q9 (2SC31138) and rectified by DS and D6 to
achieve squelch control. The squelch control signal is applied
sy Q10 (28C2458Y) to control Q7. Q1t (2SA1115E) and
212 (28C31138) are OC-ampiitiers for the busy indicator.
213 prevents transient ''clicks'' when the alert function
operates and mutes the audio when the CTCSS 's being used
Rem
Rating
'Nominal canter frequency 455 He 21 eee
3 a8 arawath
=8 kr or more (from 455 He)
50 dB bandwith
212.5 krzorless trom 455 KH)
Ripple within pass bandwith 3 aBorless
within 455 He « § kH2)
toss 60 GB orless
Guaranteed attenuation 38 dB or more
(Within 455 kHz « 100 kHz)
Input and output impedance
20K
Table 3 Ceramic filter (L72-0315-05) (A unit: L8)
[item | Rating
[Nominal center Feaueney 70.695 ME
(Pn nenamatn [eae Winer nen 30a
"Artanuation band '£25 KH or ess a 40 3B
| ff 245 kite or less at 60 48
Guaranteed attenuation 70 68 or more within fy 1 Miz
(Spurious evel= 35 dB or more)
| 80 48 oF more
| within fy 21910 kien 20 Khe) |
| Fiosle [1.0 68 or less
Loss 15 6B or oss i
Terminal imoedonce [Sao 10RF 1
Table 1 MCF (L71-0216-05) (A unit: L4)
vee
(Tom Rating
Genter frequaney {f) and "255 whiz = 1 KHz or less |
deviation
Peak separation 15 KH or more
Voltage sensitivity 1523 mvinnz
Hump No hump in the ranges ShHe |
Unearty 45503 We oF more |
Ternperature characteristics 20.3% or ess
(=20°C to +60°C) (Center frequency)
Table 2 Ceramic discri. (L79-0446-05) CFY455S
{A unit: 611)
Fig. 3 MB3712 (A unit: Q14 AF power amp.)