TS-990S
13
CIRCUIT DESCRIPTION
3-5. Preamplifi er circuit
The preamplifier circuit consists of two amplifiers: pre-
amplifier 1 and preamplifier 2. Preamplifier 1 operates at
30kHz to 21.5MHz, and has a gain of approximately 9 dB.
Preamplifi er 2 operates at 21.5 to 60MHz, and has a gain of
approximately 22 dB.
Preamplifier 1 is a noiseless feedback amplifier of the
transformer-feedback type, and incorporates a push-pull cir-
cuit in order to improve the IMD (Intermodulation Distortion)
characteristics. Preamplifi er 2 uses a bipolar transistor (Q20)
and forms a grounded emitter circuit.
The preamplifi er can be passed by turning off the P.AMP
display with the [P.AMP] key (Refer to Table 8.).
Fig. 8 Preselector circuit
ATT
ATT
0dB
1dB
2dB
PRESEL AMP
RX unit
(X55-313 A/2)
PRESEL unit
(X42-343 B/10)
PRESEL
through path
Preselector circuit
Fig. 9 Confi guration of the preamplifi er
PRE AMP2
OFF
PRE AMP1
OFF
Fig. 10 Preamplifi er 1 circuit
L39
L32
L33
Q25
Q26
L34
14V
14V
L44
14V
L40
14V
Output
Input
1t
3t
5t
4.5t
4.5t
4.5t
4.5t
1t
3t
5t
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