Cobra 19 Plus Manual page 3

The most important part of VCO circuitry is a voltage controlled
variable
capacitance dépends on DC voltage applied to its cathode.
Controlling dc Voltage
◄ ------------ Varactor Diode
T
___
The varactor diode is responsible for setting VCO frequency, and
once set
The VCO frequencies are chosen in 16 to 17 MHz range as shown on
table 1.
10.24MHz.
10.24 +
For receiver mode
Example, channel 1:
26.965 -
The above first
crystal oscillator
oscillator.
10.695 -
As can
16.27MHz
channel
incorporated
and the
is applied to the IC-202 through pin 19, the programable divider
will divide
sampling signal.
For the receiver mode the programable divider will automatically
change to divide the VCO frequency by 3254.
16270
Note that
dividing the
instead of
transmit/receive mode VCO frequencies.
19 PLUS -2-
capacitor called
Voltage Dependent
0 Capacitor
it régulâtes the VCO frequency against the reference.
To obtain transmit
As an example
16.725 = 26.965MHz
the VCO is used as a first local oscillator.
16.27 = 10.695MHz
IF of
frequency
10.24 = 0.455MHz
be seen above the VCO frequency shifts from 16.725 to
when changed
1. The shift
inside the PLL IC-202 between the selector switch
VCO divider (programable).
incoming VCO
16,725-J— 3345 = 5kHz
3254 = 5kHz
the reference
10.24MHz by
10kHz for division
varicap or
signal the
for channel
10.695MHz is mixed again with 10.24MHz
which serves as the second local
from transmit
is accomplished
When transmit logie signal
frequency by
frequency of
2048 times.
convenience).
varactor diode
0 ___________
DC Voltage
VCO is mixed with
1:
to receive for the same
by "read only memory"
3345 to produce 5kHz
5kHz is obtained
(5kHz reference is used
See table 1 for
whose
by