Frequency Synthesizer System-continued

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 oscillator, which is independent

the carrier frequency. For ex-

of the receive-transmit condition, ranges

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 oscillator, 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 generator, 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 comparator. The phase comparator