Yaesu FT-1900R, Technical Supplement

Page: 8 / 34

8
Circuit Description
TX APC Circuit
A portion of the power amplifier module output is
rectified by
D1022 (
1SS321
), then delivered to APC
Q1038 (
LM2904PWR
), as a DC voltage which is pro-
portional to the output level of the power amplifier
module.
The APC Q1038 (
LM2904PWR
) is compared the rec-
tified DC voltage from the power amplifier module
and the reference voltage from the main CPU Q2002
(
HD64F2266TF13
), to produce a control voltage,
which regulates supply voltage to the power ampli-
fier module
Q1030 (
RA60H1317M
), so as to main-
tain stable output power under varying antenna
loading condition.
PLL
A portion of the output from the VCO Q1009
(
2SC5231
) passes through the buffer amplifier
Q1010 and Q1017 (both
2SC5374
), then delivered
to the programmable divider section of the PLL IC
Q1011 (
MB15A01PFV1
), which divided according
to the frequency dividing data that is associated with
the setting frequency input from the main CPU
Q2002 (
HD64F2266TF13
). It is then sent to the phase
c o m p a r a t o r s e c t i o n o f t h e P L L I C Q 1 0 1 1
(
MB15A01PFV1
).
The 21.25 MHz frequency of the reference oscillator
circuit made up of
X1001 is divided by the reference
frequency divider section of Q1011 (
MB15A01PFV1
)
into 4250 or 3400 parts to become 5 kHz or 6.25 kHz
comparative reference frequencies, which are uti-
lized by the phase comparator section of
Q1011
(
MB15A01PFV1
).
T h e p h a s e c o m p a r a t o r s e c t i o n o f Q 1 0 1 1
(
MB15A01PFV1
) compares the phase between the
frequency-divided oscillation frequency of the VCO
circuit and comparative frequency and its output is
a pulse corresponding to the phase difference. This
pulse is integrated by the charge pump and loop fil-
ter into a control voltage (VCV) to control the oscil-
lation frequency of the VCO
Q1009 (
2SC5231
).