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Page Title:
Receive Operation |
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|  TM
11-5820-919-40-1
RECEIVE
OPERATION
80 MHz + 5 MHz - Xmt Audio
b.
(84.999 MHz)
2-14.
Assume that the receive rf (Rcv
The 75-MHz crystal filter passes
74.999
RF) signal is 2 MHz with a 1-kHz voice
MHz (USB) or 75.001 MHz (LSB).
signal. The 2-MHz Rcv RF signal is
routed from the antenna, through the L-C
The automatic level control (ALC)
2-9.
network and harmonic filter to the
circuits maintain the signal level
mixer. The 2 MHz (2.001 MHz USB, 1.999
required to produce the 20-watt output
MHz LSB) is mixed with 77 MHz LO to pro-
power for the radio set. The ALC cir-
duce 74.999 MHz (USB) or 75.001 MHz
cuits receive feedback from the power
(LSB).
The output of the mixer is
amplifier or antenna tuner.
routed through the 75-MHz crystal filter
and the 75-MHz amplifier, and mixed with
The output of the 75-MHz crystal
2-10.
70 MHz (USB) or 80 MHz (LSB). The
filter is mixed with 77-105 MHz LO from
resulting mixer outputs, 4.999 MHz (USB)
The generation of the
the synthesizer.
or 5.001 MHZ (LSB), is routed through
77-105 MHz LO signal is controlled by
the 5-MHz crystal filter, through the
the frequency selector switch settings
automatic gain control (agc) circuits,
on the control panel.
For example, if
and mixed with the 5 MHz LO. The mixer
the frequency selector is set to 2 MHz,
produces the 1-kHz (Rcv) Audio which is
77 MHz is generated and mixed. If 3 MHz
routed through the audio filter to the
is selected, 78 MHz is generated; if
earphones.
29.999 MHz is selected, 104.999 MHz is
If 2 MHZ is selected, the
generated.
mixer produces the following:
AUTOMATIC
IMPEDANCE
1.
Upper
sideband
selected
2-16. The antenna tuner module automat-
a.
77
MHz
+
74.999
MHz
(151.999
MHz)
ically matches the characteristic imped-
ance of the selected antenna to that of
77 MHz - 74.999
MHz
(2.001
MHz)*
b.
the radio set (50 ohms).
Note that the
impedance of the antenna varies with
2.
Lower
sideband
selected
frequency, because its impedance has
both reactive and resistive components.
77 MHz + 75.001 MHz (152.001 MHz)
a.
Instead of selecting a different antenna
each time frequency is changed, the
77 MHz - 75.001
MHz
(1.999
MHz)*
b.
antenna's electrical characteristics
The electrical character-
are changed.
The 0.3 to 1 watt (PEP) amplifier
istics of the antenna are changed in
in the first frequency converter rejects
the antenna tuner module by adding dif-
the 151.999 MHz or 152.001 MHz. The
ferent inductors and capacitors between
2.001-MHz signal (USB), or 1.999-MHz
the power amplifier and antenna.
Each
signal (LSB), is amplified up to 0.25
time an inductor or capacitor is added,
watt, then amplified again to 20 watts
the standing wave ratio (vswr) and/or
by the 20-watt amplifier.
impedance is checked. When the vswr
drops below 1.5:1, this indicates that:
The 1.999- or 2.001-MHz 20-watt
2-12.
(1) the antenna tuner module has added
signal (Xmt RF) is routed through the
the correct capacitor and inductor, and
harmonic filter for further filtering
(2) the antenna's electrical characteris-
tics are matched to the applied frequency.
and through the L-C network of the
antenna.
Once this match has been accomplished,
the required inductor and capacitor will
remain switched into the network until
*Indicates
the
desired
signal
retuning is required.
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