Note:
If you find d ifficulty to obtain SWR readings smaller than 3 (ratio 1 is ideal though very
hand to gain), consult the dealer to détermine how to mach your antenna to your
JUMBO.
Maintenance and
Adjustment
The transceiver is specifically designed for the environment encountered in the base station use. The
use of fu lly solid state circuitry and its rugged style resuit in high reliability. Should a failure occur,
however, replace parts only with identical parts. Do not substitute. Refer to the Schematic Diagram
and Replacement Parts List in this manuał. If the performance described in the
Operation
section
is not obtained, review the
Installation
section to insure that proper procedures were followed. If a
problem still exists, refer to your
НАМ International
dealer.
Circuit Description
The transceiver is a 120 channel CB radio which uses a phase locked loop [PLL] system of frequency
synthesization to produce the crystal controlled channel and IF signais used in operation of the
transmitter and receiver sections of the unit. The basie PLL system is comprised of a free-running
voltage controlled oscillator (part of IC2), a phase detector, a reference crystal oscillator (Q3) and a
programmable divider (IC I), as seen in diagram below.
P LL Theory (PT0S006 Circuit Board)
IC 2
The voltage controlled oscillator [VCO] opérâtes in the frequency range of 17.5550 to 18.4450 MHz
in the AM/FM/USB mode and 17.5535 to 1 8.4435 MHz in the LSB mode, and is used to produce two
output signais: #1 ; 37.660 to 39.000 MHz in the AM/FM/USB mode and 37.657 to 38.997 MHz in
the LSB mode, #2; at 2.55 to 2.11 MHz. Reference frequency oscillator Q4 oscillâtes at 10.0525,
10.165, or 10.2775 MHz in accordance with the Band Selector switch (1.5 kHz lower when LSB
mode). Its output is fed through the band-pass filter [BPF]/doubler resulting in an output signal,
20.105, 20.33, or 20.555 MHz in accordance w ith the band selected (3 kHz lower when LSB mode).
This signal beats with the VCO free-running signal producing a 37.66 to 39.0 MHz in the AM,FM/
USB mode and 37.657 to 38.997 MHz in the LSB mode, which is fed to the receiver first mixer
[Q22] and also to IC3 (on main circuit board PTBM059), the transmitter mixer. The second VCO
output signal, at 2.55 to 2.11 MHz is fed to the programmable divider in IC I. Simultaneously the
10.24 MHz output of Q3 [through the buffer.Q2] is applied to the programmable divider in IC1 and
is divided down in 10 kHz Steps. As a channel is chosen by the Channel Selector switch [SW-1 on
PTS-W076], and
N
code signal is applied to the terminais [pin No. 9 to 15 of IC I] on the program
mable divider in IC I, to preset the divider. The tw o signais, the crystal oscillated signal [10.24 MHz]
from Q3, and the signal from the VCO via the lowpass filte r [ LP F ] and buffer [in the I Cl ], are com-
pared in the phase detector of ICI and the phase detector produces a DC output voltage derived
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