Ray Pe tit, 'd7GFM             CCWN76:93
P.O. Box 51

Oak Harbor, Wa. 98277



                  FOR ccAl
A SYNfHESIZED LOCAL OSCILLATOR SYSTEM@,RECEIVERS AND THANSMITTERS



Figures 1 and 2 are diagrams of a phase-locked b.f O. and a
phase-locked 5-05 MHz "VFO" , which when used together with a
9-MHz i.f. give you the r.f. portions of a CCW station capable
of operating on 100 switch-selected frequencies spaced 10 Hz
apart. Although I have hhosen the range from 14,050 to 14,051
kHz, you can modify the circuit easily for any 1-kHz range from
25 kHz above the lower edge of a band to 100 kHz above the
lower edge. Also, changing bands is merely a matter of changing
the main oscillator crystal in Fig. 2 and 3 small capacitors.
Here is how the b.f.o. works. The 9.001 MHz oscillator can be
tuned slightly by varying the control voltage on D11 the Motorola
MV104 dual varactor diode . T et's suppose the control voltage is
set at 2.5 volts, its center value, and at this makes the oscillator
frequency exactly 9.001 MHz. @;2 and @J make a differential
amplifier which serves as a buffer going to the output and as a
TTL logic-level driver. The 74LS74 receives the I-MHz signal
from your standard. Every low-to-high transition of the clock
input causes the logic state at the D input to be transferred to
the output. Suppose the clock input was at exactly 9. MHz.
Since the D input signal is 1 kHz off frequency from the clock,
at the low-to-high transitions of the clock the logic level
appearing at the D goes from low to high and back 1000 times