Thus, only F3 or F4 programming is enabled
during function-tone operation. F1 or F2 switch
operation generates only the reset pulse, which
resets U7B, if set, and enables only the F1 or F2
programming. PTT-switch operation also
generates only the reset pulse, which insures
that only F1 or F2 programming is enabled
during function-tone-timer operation. Paired-mode
programming also activates all sections of U5,
which connects U10 latch Q to the reset input of
the other latch of the pair. If one of the pair of
latches is set, the other consequently is reset.
In the 1-of-N mode, upon power up, the F1
latch is set with a 470-ms pulse at U10-12 by
C28 through CR4. A 47-ms set pulse is also
applied to the F4 latch by C8 through U3-11,10
and CR2. A 100-ms reset pulse generated by
C13 is applied to all latch reset inputs. Only the
F1 latch, therefore, is set.
In the paired mode, the C13-to-latch-reset-input
path is short-circuited effectively by the
activated analog gates U5. Both the F1 and F4
latches receive a set pulse during power up and
both become latched.
Main PCB Receive Circuits
Selected RX signal from the upper PCB is
applied to the selected RX compressor at
U25-15 and U25-11. Maximum gain of the
compressor (actually an automatic-level-control
or ALC circuit) is determined by the bias voltage
on capacitor C66. This bias voltage is set by
R73. Input signals are full-wave rectified within
U25 and applied to C66. When the rectified
input signal exceeds the bias set by R73, it
charges C66 to a higher voltage, which lowers
stage gain and thus maintains a near-constant
average output signal at U25-10 for all signal
inputs above the bias threshold.
Output signal at U25-10 is connected to peak
detector U22-8,9,10,12,13,14. High-level,
short-duration peaks cause output at U22-8 or
U22-14, which quickly charges C66 through
R61 and CR17, and reduces U25B stage gain.
Output signal at U25-10 also drives selected RX
2175-Hz notch/bandpass filter through U16-8,9.
Bandpass output at U30-8 is amplified and
rectified by the U21-8,9,10,12,13,14 circuit.
Detector output at U21-14 lights the TX LED
through U18F whenever parallel console PTT
tone is present on the selected line. The TX LED
is also energized by PTT-switch operation
through another path.
Bandpass-filter output is summed with
unfiltered signals at U30-2, causing a sharp
2175-Hz notch to appear in the summed output
at U30-1 when the two signals have been
adjusted for equal amplitude by R126 and for
180° phase differential by R124.
Notched output signals from U30-1 are
conducted through U26-4,3 and R75 to the high
side of the selected RX volume control on the
switch PCB and then to the selected RX speaker
through U19, a power-amplifier bridge. Analog
gates U16-8,9 and U26-4,3 are disabled during
PTT, intercom, and tone burst, unless the unit
has been programmed for duplex operation.
The unselected audio circuits are identical to
the selected audio circuits, except that the PTT
tone detector has been deleted.
Audio from selected RX, unselected RX, and
TX (sidetone) is summed by U31-1,2,3 and
applied to an optional handset.
Audio from the above sources is also summed
by U31-5,6,7 and applied to an optional
VU-meter circuit.
Insertion of a phone plug into the headphone
jack disconnects both speakers from the power
amplifiers. U27-1,2,3 and U26-11,10 enable
sidetone during headphone use.
16
Summary of Contents for VEGA C-5110B
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