Realistic RadioShack TRC-490-18 Service Manual
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TRC-490-18
CUSTOM MANUFACTURED FOR TANDY CORPORATION
OWNER'
MANU
PLEASE READ BEFORE
USING THIS EQUIPMENT
EAT. NO.
1-9490
Your REALISTIC TRC-490-18 is a completely solid-state AM/SSB Transceiver designed for the Citizens
Band Radio Service. It uses a trequency synthesizing circuit with Digital Phase Locked Loop techniques
to provide crystal-controlled transmit and receive operation on all 18 channels. The PLL circuitry
assures ultra-precise frequendy tontrol. You can use your TRC-490-18 Transceiver on any one of the 18
channels in the conventional AM mode, plus the same 18 channels in either the Upper Single Sideband
mode or the Lower Single Sideband mode.
This flexibility not only doubles the effective number of channels from 18-54, but SSB also increases
the effective range of communication because all the power is concentrated in one sideband to provide
100% talk-power. Single Sideband reception also adds advantages in sensitivity and selectivity, plus
lower single-to-noise. This of course also contributes to an increase in operating range.
The TRC-490-18 has been carefully designed for ease of operation. You can select AM, Upper Sideband
or Lower Sideband with the simple change of a 3-position switch. Transmission is simple too—just press
the microphone button. Ordinarily an SSB signal will reach farther and be heard more clearly than
an equivalent AM signal. SSB reception is simple—just adjust the CLARIFIER control to bring in the
voice Transmissions.
We've added all the other most wanted features for optimum communications — RF Gain control,
Squelch, Clarifier, PA, switchable Automatic Noise Limiter and Noise Blanker circuits, R F-S meter,
Crystal Lattice Filter, Instant Channel button and LED Channel indicator.
The Squelch circuit is a special hysterisis type. This means it .is immune to signal fading which often
results in squelch
-
chopping". Another special feature from Radio Shack.
The TRC-490-18 is designed to operate from 12 volt DC negative or positive ground electrical systems, or
from 240 Volt AC power.
For your own protection, we urge you to record the Serial Number of this unit in the space provided.
You'll find the Serial Number on the back panel of the unit.
Serial Number
WARNING: To prevent fire or shock hazard, do not expose this Transceiver to rain
or moisture.
SPECIFICATIONS
GENERAL:
Channels
Frequency Range
Frequency Control
Frequency Accuracy
Operating Temperature Range
18 Channels for AM, Upper Side Band and Lower Side Band,
utilizing Digital Circuitry.
27.015 MHz to 27.225 MHz
Digital (Phase Lock Loop) Synthesizer
±135 Hz
-20°C to +50
°
C
Power Requirements
Antenna
Microphone
Speaker
13.8V DC (12-16 volts DC, negative or positive ground) or
240V AC (50 Hz)
52 ohm (Coaxial connector)
600 ohm Dynamic Type
8 ohm, 2.5 Watt
Size
4"(H) x 13-1/2"(W) x 11-1/2 (D) 10 x 34 x 29 cm
Weight
Accessories
RECEIVER:
Max Sensitivity
Sensitivity for 10 dB MI
AGC Figure of Merit 100 mV for
10 dB Change in Audio Output
Overload AGC Characteristics
from 100 mV to 1000 mV
Overall Audio Fidelity at 6 dB Down
Adjacent Channel Selectivity
Image Rejection (42.6 MHz)
IF Rejection
Maximum Audio Output Power
Squelch Range
Receiver Clarifier Range
Battery Drain at no Signal
Battery Drain at Max. Output Power
AC Power Drain
14 Lbs. (approx.) (6.5 kg)
: DC Cord with in-line Fuse, Microphone and Microphone
Hanger and Mounting Brackets
AM, 0.5
µV
SSB, 0.25
AM, 0.5 µV or better
SSB, 0.25
µV
µV or better
90 dB
±3 dB
300 — 2100 Hz
70 dB
90 dB
85 dB
4 Watts
Adjustable to 1 mV
±1.25 kHz, variable
500 mA
1,500 mA
At no Signal — 40 Watts
At Max. Output Power — 60 Watts
TRANSMITTER:
Max. Output Power
Spurious Emission
Modulation Frequency Response
(1 kHz, 0 dB reference)
Lower at 450 Hz, EIA
Upper at 2.5 kHz, El A
Microphone Sensitivity
AM : For 50% Mod.
SSB : For 4 Watts PEP
Microphone Amplifier Circuit
Dynamic Range
Battery Drain
AC Power Drain
PUBLIC ADDRESS AMPLIFIER:
Maximum Output Power
AM, 4 Watts FCC
SSB, 12 Watts FCC
-65 dB or better
AM, -6 dB
AM, -6 dB
AM, 0.4 mV
SSB, 0.4 mV
AM, 60 dB (between 98% and 80% modulation)
SSB, 60 dB (between 12W P.E.P. and 10W P.E.P.)
At no Modulation — AM/Less than 2,400 mA
SSB/Less than 1,000 mA
At Max. Output Power — AM/Less than 3,000 mA
SSB/Less than 2,700 mA
At no Modulation — AM/65 Watts
SSB/45 Watts
At Max. Output Power -- AM/100 Watts
SSB/100 Watts
4 Watts
INSTALLATION
CAUTION: Do not attempt to operate your Transceiver without an Antenna or dummy-load connected
to the ANTENNA jack. To do so may damage your Transceiver.
For fixed or base station operation, simply connect the AC power plug of the Transceiver to a source of
240 volt 50 Hz AC power and set DC-AC switch on the back of the Transceiver to AC. The only other
thing you require is an Antenna connection.
Safety and convenience are the primary considerations for mounting any piece of mobile equipment. All
controls must be readily available to the operator without interfering with the movements necessary for
safe operation of the vehicle. Be sure all cables are clear of the brake, clutch and accelerator. Also,
thought must be given to the convenience of passengers (will they have adequate leg room?).
Another extremely important requirement is the ease of installation and removal (for service and maintenance). Mount the transceiver so it can be slipped in and out very easily.
The most common mounting position for a transceiver of this size is under the dashboard directly over
the driveshaft hump. Do not mount the transceiver in the path of the heater or airconditioning air
stream. Be sure the chassis of the transceiver is electrically connected to the ground system of the
vehicle or boat. Use a separate ground wire to be sure.
When you have determined the best location for mounting, temporarily mount the brackets to the side
of the unit. Use the unit, with brackets installed, as a template to mark where the holes are to be drilled.
Take care when you drill holes that you do not drill into wiring, trim or other accessories. Remove the
brackets from the unit and assemble them to the dash as shown in the illustration. Mount the Transceiver
in position with bolts, lockwashers and nuts or self-threading screws.
/%;-%
/*
V
V/ /V
VV VV //
V V
13.8 DC
AC DC
FUSE
240
VAC
ANTENNA
PA
SPEAKER
EXT
SPEAKER
FOR BASE INSTALLATION
MOBILE INSTALLATION
For Negative Ground Electrical Systems: Connect the Black with stripe wire (with in-line fuse holder) to
the Accessory terminal on the ignition switch of your vehicle. Make a good mechanical and electrical
connection to the frame of the vehicle for the black (negative) wire. Set DC-AC switch to the DC
position.
For Positive Ground Electrical Systems: Connect the Black wire to the Accessory switch "hot" terminal
and connect the Black with stripe Wire to the metal frame of the vehicle. Thus, Black always goes to
negative (-) and Black with stripe! always goes to positive (+). Set DC-AC switch to the DC position.
You can use an auto accessory plug (Radio Shack Catalog No. 274-331) to connect your Transceiver to
the vehicle's cigarette lighter socket. However, it is better to connect the DC power cord directly to the
accessory terminal of the ignition switch. This will prevent unauthorized usage of the Transceiver, and
will also prevent you from leaving the Transceiver on unintentionally.
FOR MOBILE INSTALLATION
ANTENNA SYSTEM
The antenna system includes the transmission line, and it is very important that you use the correct type
of transmission line. The transmission line should be of the coaxial type and should have an impedance
equal to the antenna impedance.
Since your Transceiver is designed to operate most efficiently into a 50 ohm load, it is best to use a type
of coaxial cable with an impedance of 50 ohms. We suggest type RG-58/U for short lengths and RG-8/U
for long lengths.
Generally speaking, you should keep the length of the transmission line to a minimum. Remember that
line losses increase with frequency. Use foam-insulation coax for best results.
The above discussion is as important for reception as it is for transmission. If a mismatch exists between
the antenna and the receiver, the excellent sensitivity and signal-to-noise ratio of the receiver circuitry
will be defeated.
FIXED STATION ANTENNAS
The most popular fixed station antenna is a complex colinear or ground plane.
Beam antennas provide maximum gain and maximum directivity. The directivity can be a disadvantage
unless a rotor is used. Since a beam antenna is directional, it greatly reduces noise and interference from
all other directions. This can be a decided advantage on the CB bands where man-made noise is a
problem.
GROUND PLANE
Your Radio Shack store carries a complete line of base station CB antennas and accessories. For
maximum efficiency, we strongly recommend using an SWR meter to aid in the proper matching
between your antenna and Transceiver.
The antenna system should be adequately grounded.
Always use a lightning arrester for your antenna system.
MOBILE STATION ANTENNAS
Mobile CB antennas are one of two types. a full-length or a loaded whip. Your Radio Shack store carries
a complete line of both types of mobile antennas.
The location of the antenna has a great effect on the antenna efficiency and directivity. Antennas
mounted in the center of the roof radiate equally in all directions. A bumper-mounted antenna radiates
in a pattern directly in front of and to the rear of the vehicle, with maximum radiation directly away
from the vehicle, in a horizontal plane.
DUAL 6-ELEMENT BEAM
BASE STATION ANTENNAS
VERTICAL BEAM
Since the normal 1/
the antenna is shortened and a loading coil is utilized to provide the proper electrical length. As a result,
the overall efficiency is reduced and the nondirectional advantage is defeated. Thus, a bumper-mounted
full-length whip antenna will normally give the best results.
4
wavelength whip antenna is too long (102" [2.6m] ) for roof mounting on a vehicle,
ROOF MOUNT
A few general rules should be followed for proper installation of any mobile antenna:
1.
Keep it as far as possible from the main bulk of the vehicle.
2.
Keep as much of it as possible above the highest point of the vehicle or boat.
3.
During operation, it must be vertical. Thus, it should be mechanically rigid so it will maintain a
vertical position when the vehicle or boat is in motion.
4.
Mount it as far as possible from sources of noise (ignition system, gauges, etc.) and convenient for
transmission line routing away from these noise sources.
An antenna mounted in a boat requires a ground. This can be either the metal hull or a ground made of
tin-foil or copper sheeting. This ground should cover an area of 12 square feet (1 m
the transceiver has an adequate ground as well. If you use Radio Shack's 102" (2.6 m) Fiberglass Marine
Antenna (21-912), you won't need a ground; it has been designed with its own "ground" system.
FRONT COWL MOUNT
REAR DECK MOUNT
NOISE
Your vehicle or boat can be the cause of much noise interference. Your TRC-490-18 incorporates a
switchable Automatic Noise Limiter circuit for AM and a Noise Blanker for both AM and SSB reception.
Also, it has built-in power supply filtering. These circuits can help to reduce and/or eliminate annoying
noise.
BUMPER MOUNT
2
) or more. Be sure
Remember, your Transceiver has a very sensitive receiver and it will pick up even the smallest trace of
ignition noise. Any noise that you hear in the Transceiver is almost totally from external sources. The
receiver itself is exceptionally quiet. Steady high noise levels can not be eliminated by the internal
Automatic Noise Limiter and Noise Blanker circuits. Noise problems can not be solved internally (in the
Transceiver); they must be solved at the source of the noise.
11 you wonder if the noise is from your ignition system, the Transceiver or an external` source, try this
simple test. Turn your ignition switch off and set it to ACC (accessories). This turns off the ignition,
but supplies power to the Transceiver. Most of the noise will disappear—indicating that the source of
noise is your ignition system.
This interfering noise can be generated anywhere in the electrical system of the vehicle or boat. The first
step in reducing or eliminating this noise is to locate the source of the noise.
IGNITION SYSTEM
The most common source of noise is the ignition system. This noise can be identified by the fact that, it
engine. It consists of a series of popping sounds occurring at a regular rate
varies with the speed of
that will vary with the speed of the engine and stop when the ignition is turned off.
There are a number of things that can be done to reduce this type of noise:
Use only the "radio suppression type" high voltage ignition wire. Most new cars come already
1.
equipped with this type of wire.
Inspect the high voltage ignition wire and all connections made with this wire. Old ignition wire
2.
may develop leakage, resulting in hash.
If noise still persists, replace the spark plugs with spark plugs that have suppressor resistors built-in.
3.
Be sure to use the correct type for your vehicle.
Other sources of noise are: generator/alternator, regulator, gauges and static discharge. Most of these
types of noise can be effectively reduced or eliminated by using bypass capacitors at the various output
voltage points. Once again, we suggest you check your Radio Shack store for a selection of noise
reduction accessories.
the
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