Kenwood TH 78 Service Manual

Page 2

TH-78A/ E

CIRCUIT DESCRIPTION

1 Frequency configuration 0 The SUB-U receive signal becomes the 45.050 MHz first lF by
0 The TH-7e has separate pLL and lF units for the VHF and UHF doubling the VHF local oscillator signal, which is used as the
bands. so it can receive signals in both bands at the same time. '5 1093' oscillator signal (lower hetero), and is processed by

O The UHF VCO signal is doubled, and the signal before doubling the MvVHF IF circuit.
is used as a local oscillator signal, so signals can be received in . The SUBV receive signal becomes the 55-525'MH1 '5 it: by
the VHF band at the same time. using the VHF signal before the UHF-VCO doubler as the first

0 The signals can be received in the UHF band by doubling the 03 050mm signal (upper hetero). and is processed by the M-
VHF local oscillator signal. UHF IF circuit.

0 The M-UHF receive signal becomes the 58.525 MHz first IF 0 The VHF transmitter system effects reactance modulation by
when mixed with the first local oscillator signal (lower hetero), diVSCi'Y driving the V00: and amplifies the signal 10 the required
and is then mixed with the 58.070-MH2 second oscillator signal level 10 produce a transmit Signal.

(upper hetero) to produce 3455 kHz signal. 0 The UHF transmitter system applies reactance modulation to

O The M-VHF receive signal becomes the 45.050 MHz first n: the oscillator that generates half the transmit frequency.
when mixed with the ins: local oscillator signal (lower hetero), doubles the signal. and amplifies it to the required level, to pro-
and is mixed with the 45.505 MHz second oscillator signal duce atransmltsignal.

(upper hetero) to produce a 455 kHz signal,
ANT
379.47% <
GEE-QSOMNI UHF F g
erc or: sost l9§.l75~ F _
Fl (VHF) 2475mm ase-asim
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mm 550th les.os~ls3.05mz "me var
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AFAMP
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T/R SHIFT
PLL DATE EXAMPLE 2U45.A and CANAMAN VERSION

Fig. 1 Circuit conflgration by frequency

Page 96

CONTROL UNIT (X53-342X-XX) C/S

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CONTROL UNIT (X53-342X-XX)E/5

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96