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- - - - - - - - - - - - - - - - C i r c u i t Description
~
is converted to DC by charge pump section of
Q1016, and is then fed through the low-pass
filter to varactors D301 to D304 (both
1
T363)
on the VCO Unit.
Changes in the level of the DC voltage ap-
plied to D301
&
D302 affect the reactance in the
tank circuit of Receiver VCO Q301, changing
the oscillating frequency according to the
phase difference between the signals derived
from the VCO and the crystal reference oscilla-
tor. The VCO
is
thus phase-locked to the crystal
reference oscillator.
The output of receiver VCO Q301, after buff-
ering by Q305, is delivered to the Main Unit for
~.
amplification by Q1011
(2SC2759)
before ap-
plication to the 1st mixer, as described pre-
viously.
Transmitter VCO Q303
(2SC4226)
oscillates
between 144 MHz and 148 MHz according to
the programmed transmit frequency. The re-
mainder of the PLL circuitry is shared with the
receiver. However, the dividing data from the
microprocessor is such that the VCO frequency
is at the actual transmit frequency (rather than
offset for IFs, as in the receiving case). Also, the
transmitter VCO is modulated by de-empha-
sized audio applied to D303
&
D304, as de-
scribed previously.
Transmit Inhibit
When the transmit PLL is unlocked pin 7 of
PLL chip Q1016 goes to a logic low, turning on
Q1017, Q405 and Q401, which then turns off
Automatic Power Controller Q401 and Q1012
to disable the supply voltage to transmitter RF
amplifiers Q1008 and Q701, disabling the
transmitter.
Miscella~teous
Circuits
Push-To-Talk Transmit Activation
The PIT switch on the microphone is con-
nected to pin 21 of microprocessor Q2001, so
that when the PIT switch is closed, pin 21 of
Q2001 goes low. This signals microprocessor to
activate TX/RX controller Q408
(2SC2812)
on
the APC Unit, which then disables the receiver
by disabling the 9V supply bus at Q402
(288624)
to the front-end, IF, discriminator
and receiver VCO circuitry. At the same time,
Q403
(288624)
activates the transmit 9 V sup-
ply line to enable the transmitter.
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FT-2200 Technical Supplement
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