Quantcast Filter  Module  1A5 Detailed Functional Operation


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19 MHz Balanced Mixer.
TM-11-5820-873-34 Radio Set AN/URC-92 (NSN

TM 11-5820-873-34
In the first case, the positive going signal is formed into
strobe pulse when it is triggered by the pulse from the
a 100 to 200 millisecond positive differentiated pulse.
count filled detector ((c) above)
The positive differentiated pulse turns switch 1A4A6Q2
(3)  Phase Detector.  The 100 kHz reference
on Switch 1A4A6Q2 turns switch 1A4Q6Q1 on,
signal from spectrum generator 1A4A1 (a above) is
generating a blanking pulse. In the second case, the
applied to divide-by-four counter 1A4A4U11.  The 25
negative going signal is formed into a 100 to 200
kHz output from 1A4A4U11 is applied to phase detector
millisecond negative differentiated pulse The negative
1A4A4U12. The phase detector compares the nominal
differentiated  pulse  turns  switch  1A4A6Q1  on,
25 kHz output frequency of the preset counter ((2)
generating a blanking pulse In either case, the blanking
above) with the 25 kHz input from 1A4A4U11 and
pulse is applied to spectrum generator 1A4A1 (a above),
develops a DC output voltage that is proportional to the
and disables the 3rd local oscillator signal.
two signals.  The output from the phase detector is
coupled to VCO 1A4A5 (e below).
2-10. Filter  Module  1A5
e. VCO 1A4A5 (Fig. FO-3 and Fig. FO-11).
(1)  Band Oscillators.
The selected 10 MHz
Operation (Fig. FO-4)
FREQUENCY switch enables one of the three band
oscillators through one of the three transistor switches.
a. Filtering.  The filter module provides low pass
The band oscillators are Colpitts oscillators similar to
filtering in transmit mode and band pass in receive
voltage controlled oscillator 1A4A2 (b(1) above). Band
mode.  The filters have been divided among three
0 oscillator 1A4A5Q7 operates over a frequency range
different boards. Board 1A5A1 has the low pass filters
of 91.25 to 101.2499 MHz Band 1 oscillator 1A4A5Q7
for the odd number channels. Board 1A5A2 has the low
operates over a frequency range of 101.25 to 111.2499
pass filters for the even number channels.  Board
MHz. And, Band 2 oscillator 1A4A5Q8 operates over a
1A5A3 has high pass filters. Only the low pass filters
frequency range of 111.25 to 121.2499 MHz. Coarse
are used in the transmit mode. The high pass filters are
frequency tuning is provided by the action of the course
used, along with the low pass filters, for band pass
frequency  voltage  from  the  selected  10  MHz
filtering in the receiver mode. Correct filtering for each
FREQUENCY switch. Fine frequency tuning is provided
band is accomplished automatically when the front
by the DC voltage from VHF divider 1A4A4 (d(3)
panel frequency control switches are set.  Inactive
above). The output from the enabled band oscillator is
filters, for any given band, are switched to ground
coupled through amplifier 1A4A5Q11, 1A4A5Q12 to
through a 10 ohm resistor. This discharges the filter and
translator 1A4A3 (c above) and through amplifier
prevents unwanted interaction with active filters. Table
1A4A5Q9, 1A4A5Q10 and the 91 to 122 MHz bandpass
2-2 lists the filter band numbers and their corresponding
filter to receiver/exciter 1A3 (para 2-4).
frequency ranges.
(2)  Binary Coded Decimal Converter. The BCD
converter consists of two transistor switches, 1A4A5Q1
Table 2-2. Band Numbers and Frequency Ranges.
and 1A4A5Q2, that convert the ground signal from the
selected  10  MHz  FREQUENCY  switch  to  tens
complement binary coded decimal. The output from the
BCD converter is applied to the 10 MHz preset gate
(d(2) above) in VHF divider 1A4A4.
f.  Local Oscillator Blanker (Fig. FO-23). The local
oscillator blanker protects the power amplifier from
transients  caused  by  a  frequency  change  while
transmitting. When the selected 1 MHz FREQUENCY
switch setting is changed, the synthesizer may change
frequency  by  several  MHz  while  the  switch  is
momentarily open. If this occurs while transmitting, it
b. Filter Selection.  Correct filter selection for the
would result in a large transient that could damage RF
band in use is setup through wafer switches driven by a
power amplifier 1A7A1.
DC motor. The motor (B1) is mounted on the Motor
When the setting of the selected 1 MHz
Control Board 1A5A4.  Motor control is accomplished
FREQUENCY switch is changed, the "preset 20 1 MHz"
with an "open seeking" circuit comprised of relay
frequency control line will change from either:
1A5A4K1 and wafer switch 1A5A4S1. When changing
logical "0" (approximately 0.2 volts) to
the 1 MHz or 10 MHz switch of the selected frequency
logical "1" (approximately 3 volts) state
changes the band, relay 1A5A4K1 is energized thru
1A5A4S1.  The now closed contacts, 5 and 9, of
logical "1" to logical "0" state
1A5A4K1 supply + 12 VDC to motor 1A5A4B1.  The
motor simultaneously rotates the wafer switches on

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