3: Audio/Filter Board
3-4
PRC1099A-MS
3.1.2
Receive Path
The Audio/Filter board receives the receive signal through coax connector J12
(RF OUT) from the Antenna Tuner board. From J12 the receive signal passes
through single-turn transformer T1 that provides the signal for the ALC circuit
covered in “ALC Circuit” on page 3-6—the ALC circuit has no function in
the receive path.
Low-Pass Filters
After transformer T1 the receive signal passes one of the high performance,
5-pole, elliptic function low-pass filters selected by the processor as discussed
in “Low-Pass Filters” above.
High-Pass Filters
After passing through the low-pass filter, the receive signal passes through a
7-pole Chebyshev filter with a cutoff frequency of 1.6 MHz (C107, C106,
C105, C104, L17, L16 and L15). This filter provides a high level of
attenuation to signals below 1.6 MHz in the broadcast band and prevents
overload when operating in the vicinity of a powerful broadcast station. From
the high-pass filter, the receive signal is applied to coax connector J8 (RX
OUT) where the signal is routed to the Mixer board.
Off-Board
Receive Path
On the Mixer board the receive signal is up-converted from the selected
channel frequency to an IF frequency of 75 MHz, amplified, filtered, and then
down converted to the final IF of 1647 or 1650 kHz. The Mixer board is
discussed in Chapter 5. The modulated IF signal is routed from the Mixer
board to the 1650 kHz IF board where the unwanted frequencies are filtered
out and the 1650 kHz or 1647 kHz IF signal and the signal is amplified. The
1650 kHz IF board is discussed in Chapter 4.
After the 1650 kHz IF board, the modulated IF signal is returned to the
Audio/Filter board through J9 (RX IN) where it is applied to the product
detector.
Product Detector
Product detector U4 is an integrated circuit that removes the 1650 kHz IF
frequency from the receive signal leaving the audio base band signal. The
1650 kHz IF from the 1650 kHz IF board is applied to the input at pin 2. The
1650 kHz carrier oscillator (1650 kHz for USB;1647 kHz for LSB) from the
Synthesizer board is applied to the input at pin 1. The output at pin 8 is the
sum and difference frequencies from the two input signals. The sum frequency
at 3.3 MHz is filtered by C17. The difference frequency is approximately zero
as the 1650 kHz BFO and the 1650 kHz receive IF signal cancel each other
leaving the audio baseband. The audio is routed to either the squelch circuit, to
the front panel audio connectors (50 OHM RX AUDIO) through audio
amplifier U5, or to the front panel Accessory connector (600 OHM RX
AUDIO) through audio amplifier U10A.
Squelch Circuit
The squelch circuit operates by detecting the syllabic rate of change in the
human voice to switch audio off in between words and sentences in the
transmit and receive signals. The squelch is immune to impulse noise, static,
carriers, and general background noise. The squelch is preset internally and is
activated in the USB mode when the
Mode
knob is turned to the squelch
Содержание PRC1099A
Страница 4: ......
Страница 8: ......
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Страница 49: ...3 Audio Filter Board 3 14 PRC1099A MS Figure 3 2 Audio Filter Board Component Locations 738221 Rev J ...
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Страница 71: ...4 1650 kHz IF Board 4 6 PRC1099A MS Figure 4 2 1650 kHz IF Board Component Locations 738028 Rev D ...
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Страница 86: ...5 Mixer Board 5 10 PRC1099A MS Figure 5 4 Mixer Board Component Locations 738217 Rev H ...
Страница 97: ......
Страница 103: ...6 Power Amplifier Board 6 6 PRC1099A MS Figure 6 2 Power Amplifier Board Component Locations 738617 Rev C ...
Страница 117: ...7 Antenna Tuner Board PRC1099A MS 7 9 Figure 7 2 Antenna Tuner Driver Board Component Locations 738346 Rev B ...
Страница 118: ...7 Antenna Tuner Board 7 10 PRC1099A MS Figure 7 3 Antenna Tuner Board Component Locations 738027 Rev D ...
Страница 125: ......
Страница 131: ...8 Synthesizer Board 8 6 PRC1099A MS Figure 8 2 Synthesizer Board Component Locations 738025 Rev A ...
Страница 163: ...9 Processor Board 9 14 PRC1099A MS Figure 9 2 Processor Board Component Locations 738218 Rev B ...
Страница 178: ...10 Display Board 10 8 PRC1099A MS Figure 10 1 Display Board Component Location Diagram 738220 Rev G ...
Страница 181: ......
Страница 185: ...11 Junction Board 11 4 PRC1099A MS Figure 11 1 Junction Board Component Locations 738222 Rev F ...
Страница 200: ......
Страница 207: ...13 Internal Options PRC1099A MS 13 7 Figure 13 3 ALE Board Component Locations 1 of 2 738215 Rev B ...
Страница 208: ...13 Internal Options 13 8 PRC1099A MS Figure 13 4 ALE Board Component Locations 2 of 2 738215 Rev B ...
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Страница 247: ...Index 6 T Technical specifications 1 2 Transmit path 2 4 U USB 1 4 see also Modulation modes USB LSB mode V VSWR 1 4 ...