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those used for transmission, unless other-
quency and the vfo frequency (44.60 mc)
wise indicated, by subtraction of 50 kc
equals 52.60 mc.
d. The 53-mc filter passes a band of'
from the given frequency.
a. The vfo output frequency ranges from
frequencies, centered at 53 mc, to the fss
41.50 mc to 64.45 mc. The specific fre-
second mixer. The fss second mixer is
also supplied an input signal from the
quency depends on the channel selected,
100-kc  interval  oscillator  (e  below)
and whether the channel is in the high or
low band.
through the tuned net work, which re-
(1) When the low band is used, the vfo
duces spurious frequencies. The fss sec-
operates at 11.50 mc above the
ond mixer heterodynes the two signals to
carrier frequency. For example, at
produce their difference, which is the fss.
a received frequency of 33.10 mc,
i f . It is applied to the fss if. am-
the vfo frequency is 44.60 mc.
plifier.
(2) When the high band is used, the
e. The output frequency of the 100-kc
vfo operates at 11.50 mc below
interval which is independent
the carrier frequency. For ex-
ample, at a received carrier fre-
from 46.85 mc to 47.75 mc in 100-kc
quency of 68.45 mc, the vfo fre-
increments. The specific frequency de-
quency is 56.95 mc.
pends on the frequency selected by the kc
b. The vfo output (a above) is applied
tuning knob; that is, whichever 50- or
through the fss buffer and the fss first
100-kc channel point is selected. Except
mixer buffer to the fss first mixer. The
for the 0.95-mc channel point, the fre-
two buffer stages isolate the vfo from the
quency relationship is such that the out-
fss first mixer to prevent feedback of
put of the 100-kc interval oscillator is
sidebands created in the mixer. The fss
46.85 mc above a specific 100-kc channel
first mixer receives another `input from
point (0.00 mc, 0.10 mc, 0.20 mc, etc) and
the pulse generator, `which is driven by
46.90 mc above a specific 50-kc channel
the output of the 1.0-mc crystal oscillator.
point (0.05 mc, 0.15 mc, 0.25 mc, etc).
(During transmission, the output of the
At the 0.95-mc channel point, the 100-kc
interval oscillator is 45.90 mc above the
1-mc crystal and, therefore,
kc indication; therefore, with the kc tuning
that of the pulse generator, do not change
in frequency.) The sinusoidal output of the
knob set at the 0.95- or 0.00-mc channel
l-mc crystal oscillator is applied to the
point, the 100-kc interval oscillator fre-
pulse generator where it is shaped into
quency will be 46.85 mc; at a 0.05- or
pulses that are rich in harmonic content.
0.10-mc channel point, the frequency will
The output of the pulse which
be 46.95 mc; at a 0.15- or 0.20-mc chan-
is applied to the fss first mixer, is a
nel point, the frequency will be 47.05 mc;
frequency spectrum ran gin g from 1
at a 0.85- or 0.90-mc channel point, the
through 12 mc in l-mc increments. (During
frequency will be 47.75 mc.
(1) The fss if. will always be 5.65 mc
transmission, the frequency spectrum
does not change.) The fss first mixer
at the 100-mc channel points dur-
heterodynes the two inputs and applies the
ing reception, and 5.60 mc during
resultant spectrum to the 53-mc filter.
transmission.
c. Since the frequencies developed in
(2) The fss if. will always be 5.60 mc
the fss first mixer output will be the two
at the 50-kc channel points during
original signals plus their sum and dif-
r e c e p t i o n and 5.55 mc during
ference, a frequency (plus its upper and
transmission.
lower sidebands) which approaches the 53-
f. The fss if. amplifier has a power
mc bandpass will always be generated,
gain of approximately 40 db to provide
regardless of the vfo output frequency.
adequate limiting for a constant output
For example, when the vfo is operating
amplitude. The fss if. amplifier output is
at 44.60 mc, the sum of the eighth harmonic
applied to the discriminator and to the
(8 mc) of the pulse generator output fre-
phase The phase comparator
6

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