Vertex Standard VX-600 Service Manual page 15

The resulting DC squelch control voltage is passed
to pin 19 of the microprocessor
is received, this signal causes pin 6 of
( ) to go low and pin 89 of
high. Pin 6 of
( ) and
supply voltage to audio amplifiers
, while pin 89 makes
the green (Busy) half of the LED off, when pin 6 of
is low and pin 89 of
Thus, the microprocessor blocks output from the au-
dio amplifier, and silences the receiver while no sig-
nal is being received, and also during transmission.
When a carrier appears at the discriminator, noise
is removed from the output, causing pin 19 of
to go low and the microprocessor to blink the busy
LED via .
The microprocessor then checks the DTMF decoder
chip on the Optional Unit, the CTCSS and the CDCSS
code for DTMF or CTCSS or CDCSS code squelch
information, if enabled, respectively. If not transmit-
ting and CTCSS or CDCSS is not activated, or if the
received tone or code matches that programmed, the
microprocessor stops scanning, if active, and allows
audio to pass through the audio amplifier
( ) to the loudspeaker by enabling
the supply voltage to it via
Transmit Signal Path
Microphone Amplifier
Speech input from the microphone is amplified in
( ), is filtered, and is sent to
( ) and sent to the Dummy Unit (or Op-
tional Unit). The audio which returned from the
Dummy Unit passes through
pre-emphasized.
The processed audio is then mixed with a CTCSS tone
generated by microprocessor
( ) for frequency modulating the PLL
carrier up to ±5 kHz from the unmodulated carrier at
the transmitting frequency.
If an external microphone is used, PTT switching is
controlled by (
croprocessor when the impedance at the microphone
jack drops.
. If no carrier
signals (
( ) to disable the
( ) hold
is high.
, and
(
and delivered to
), which signals the mi-
If a CDCSS code is enabled for transmission, the code
is generated by
( ) for CDCSS modulation.
to go
If DTMF is enabled for transmission, the tone is gen-
),
erated by the microprocessor
the splatter filter (
and
Also, the tone is amplified for monitoring in the
loudspeaker.
Noise Canceling Microphone Circuit
Two signals from separate internal microphones
(main and sub) are fed to the positive input (sub)
and to the negative input (main) and of
(
both main and sub, the main signal will be canceled
at the output of Pin 1 of
from nearby sources not directly connected to the
transceiver enters the main and sub input at the same
signal and, in the absence of (stronger) voice input,
is therefore canceled out.
When a signal is only input to the main microphone,
and there is no signal at the sub microphone, the
main signal is passed as-is from
Drivers and Final Amplifiers
The modulated signal from the VCO,
and (
) and amplified by
. level transmit signal is then applied to the Power
Module
to a maximum of 5 Watts of output power.
The transmit signal then passes through the antenna
switch
suppress harmonic spurious radiation before deliv-
ery to the antenna.
) to be Automatic Transmit Power Control
RF power output from the final amplifier is sampled
by
( ). The resulting DC is fed back through
(
ing control of the power output.
The microprocessor selects either "High" or one of
three "Low" power levels.
Circuit Description
and delivered to
) in place of speech audio.
). If the same signal level is present at
. In other words, noise
), is buffered by
(
( ) for final amplification up
( ), and is low-pass filtered to
and , and is rectified by
) to the Power Module, provid-
and applied to
.
(
) . The low-
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