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by the
control on the Vol Unit, is passed to
SQL
the squelch switching section within Q2011.
While no carrier is received, pin 14 of Q2011
(the Scan Stop line) remains low, signaling pin
7 of microprocessor Q1006 on the Control Unit
to keep the green (Busy) half of the UHF
LED off, and holding the AF MUTE
AIR/BUSY
line to the MIC AF Amp Unit high to block
UHF receiver audio from passing through
analog gate Q1406 while no signal is being
received, as well as during transmission.
When a carrier appears at the discriminator,
noise is removed from the output, causing pin
14 of Q2011 to go high and signaling micro
processor Q1006 to activate the
microprocessor then checks CTCSS chip
Q1010
(MX265LH)
and DTMF decoder chip
Q1007
(TC35305F)
for CTCSS or DTMF code
squelch information, respectively. If not trans
mitting and tone squelch is not activated, or if
the received tone matches that programmed,
the microprocessor stops scanning, if active,
and allows audio to pass through muting gate
Q1406 to the amplifier and loudspeaker.
UHF Single-Band Dual Receive
When UHF single-band dual receive opera
tion is active, a portion of the received UHF
passing through the antenna switching net
work (and applied to the UHF front end) is
delivered to diode D3024 on the 144 Mother
Unit for application to the U /U Rx Unit
daughter board, also on the 144 Mother Unit.
Here, the signals are band-pass filtered and
amplified by Q6002 and Q6003 (both
4325)
before application to mixer Q6001
4537).
This mixer also receives the third
harmonic of the 144-MHz VCO Unit. The re
sulting 15.25-MHz sub-receiver 1st IF signal
(U/U IF) is applied to the VHF receiver IF
chain just before monolithic filter XF3002, and
is then handled just as a VHF signal would be
in VHF operation.
Transmitter Audio Stages
Speech input from the microphone is deliv
ered to the Mic/
AF
tion and pre-emphasis by Ql 404-1 ( 1 4
LM324DB).
Unless the microphone is dis
abled, the audio is then passed through Mic
Mute gate Q1406-2 ( 1 ;4
(instantaneous deviation control) utilizes the
Uf'Jl t:9n "'--'--!-- 1 C'---- J
LED. The
BUSY
2SC-
(2SC-
Amp Unit for amplifica
NJU40668W).
The IDC
__ - - -'-
symmetrical saturation characteristics of op
erational amplifier Q1404-2 (1/4
process transmitted audio. This then passes
through the splatter filter consisting of Q1404-
(%
3
LM32408),
C1450 which form a 3-pole Butterworth Filter
ON
(approx. 2.8 kHz cutoff) before delivery to the
modulator.
If VOX is enabled, a sample of the output of
the IDC stage is used to activate the transmit
ter via Q1404-4 ( 1 /4
essor Q1005
(HD4074629H).
If Tone Burst or DTMF is enabled for trans
mission, the tone is generated by microproc
essor Q1005, buffered by Q1403-2 and applied
to the iDC stage in place of speech audio. Also,
the tone is amplified for monitoring in the
loudspeaker, as mentioned before. The micro
processor closes Mic Mute gate Q1406-2 when
transmitting a tone, or when transmission is
disabled.
The modulating audio is delivered first to
_
the Control Unit, where it may pick up a gen
erated CTCSS tone, and then through the
modulation potentiometers on the Interface
Unit. The transmit audio is next delivered to
RF
both Mother Units, where it is either disabled
(on the receiving band) by Q3018 (VHF) or
Q2010 (UHF, both
modulating varactors D203 (in the UHF VCO)
or D605 (in the VHF transmitter VCO), fre
quency modulating the PLL carrier up to ± 5
kHz from the unmodulated carrier at the tran
smitting frequency.
Late VHF Transmit Stages
On the 144 VCO Unit, the modulated signal
from VHF transmitter VCO Q602
is buffered by Q603
to the 144 Mother Unit for amplification by
(2SC4245),
Q3002
tion by VHF PA module Q901
the 144 PA Unit. The transmit signal then
passes through antenna t/r switch D901 be
fore returning to the duplexer network on the
144 Mother Unit and then a 3-pole low-pass
filter consisting of L3001, L3002, C3016, C3005,
C3006 and C3019 (mounted on the 144 Mother
Unit) and L2006, C2021, C2022 and C2031 and
the 2-pole LPF (L2002, L2003, C2031, C2022,
C2007, C2023, C2032 and C2073) mounted on
LM324DB),
R1451-53, C1446, C1449 and
LM324DB)
and microproc
DTC144EE),
or delivered to
(2SC4226)
(2SC4226)
and returned
and then final amplifica
(M677 48L)
to
on
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