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QUIZ 2
1. When no FM modulation is present, the incoming
signal frequency is . . .
(a) DC
(b) fixed
(c) minimum
(d) maximum
2. An increase in the carrier frequency due to
modulation is called . . .
(a) detection
(b) negative deviation
(c) positive deviation
(d) peaking
3. The amplifier known as the "limiter" is used to . . .
(a) remove noise
(b) detect FM signals
(c) increase audio output
(d) improve linearity
4. Lowering the value of the resistor across the
quadrature coil will . . .
(a) reduce bandwidth
(b) remove noise
(c) improve gain
(d) improve linearity
5. Positive deviation will cause the gated output
pulse to . . .
(a) decrease in width
(b) increase in width
(c) decrease in amplitude
(d) increase in amplitude
BLOCKS 3 & 4 - CONVERTING TO 455kHz
Theory of Operation
The first local oscillator should be set at 133.3MHz
to 137.3MHz for the 2 meter band and 39.3MHz to
43.3MHz for the 6 meter band. This oscillator is
free-running varactor-tuned.
converts the RF input to an i-f frequency of
10.7MHz. This i-f signal is then filtered through a
ceramic filter and fed into the second mixer. If the
oscillator of the second mixer is precisely set at
10.245MHz, it will produce an output containing the
sum (20.945MHz) and the difference (0.455MHz or
455kHz) frequencies. This 455kHz signal is then
sent to the limiter, detector, and audio circuits.
b
10.
a,
9.
b,
8.
d,
7.
d,
6.
The first mixer
6. When the quadrature detector is made more
linear by separating the peaks, the output . . .
(a) increases
(b) remains the same
(c) produces more distortion
(d) decreases
7. The function of the squelch control is to remove:
(a) high frequencies
(b) fading
(c) static during transmissions
(d) non-transmission static
8. A decrease in the carrier frequency due to
modulation is called . . .
(a) detection
(b) negative deviation
(c) positive deviation
(d) peaking
9. An FM detector converts frequency changes to:
(a) DC changes
(b) resistance changes
(c) capacitance changes
(d) modulation index
10. The coil in the quadrature detector is used to
produce . . .
(a) DC voltage
(b) phase shift
(c) frequency shift
(d) amplitude peaking
a,
5.
d,
4.
a,
3.
c,
2.
b,
1.
The mixers are doubly balanced to reduce spurious
(unwanted) responses. The first and second mixers
have conversion gains of 18 to 22dB respectively.
Conversion gain is the increase in a signal after the
signal has been converted to a new frequency and
amplified.
For both converters, the mixers are
designed to allow the use of pretuned ceramic
filters.
After the first mixer, a 10.7MHz ceramic bypass filter
is used. This eliminates the need for special test
equipment for aligning i-f circuits. The ceramic filter
also has a better aging and temperature
characteristic than conventional LC tuned circuits.
-19-
Answers:
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