Cobra 21 LTD ST User Guide
21LTDST.MANUAL.REV.QX 9/25/98 10:59 AM Page 1
OPERATING INSTRUCTIONS FOR YOUR
40 CHANNEL
CITIZENS BAND
2-WAY MOBILE RADIO
Model
21 LTD ST
Cobra Electronics Corporation
6500 W. Cortland Street
Chicago, IL 60707
PRINTED IN HONG KONG ©COBRAELECTRONICS CORP. 1997 480-221-P-001
21LTDST.MANUAL.REV.QX 9/25/98 10:59 AM Page 3
How To Use Your
Citizens Band
2-Way Mobile Radio
Model 21 LTD ST
Contents Page
The CB Story ............................................................................................1
SoundTracker System ............................................................................1
Specifications........................................................................................2,3
Installation
Location..................................................................................................4
Mounting Connections....................................................................4, 5
CB Antenna ..........................................................................................6
Ignition Noise Interference ................................................................7
In House Operation..............................................................................7
Operation
Controls and Indicators ............................................................8, 9, 10
Operating Procedure to Receive ......................................................11
Operating Procedure to Transmit....................................................12
How SoundTracker Works................................................................13
Maintenance and Adjustment ............................................................14
Appendix
Ten Code..............................................................................................15
A Few Rules That Should Be Obeyed ............................................16
How Your CB Can Serve You ..........................................................16
Warranty Service Instructions ............................................................17
Limited Two Year Warranty ................................................................18
Accessories..................................................................Inside Back Cover
The CB Story
The Citizens Band lies between the shortwave broadcast and 10-meter Amateur
radio bands, and was established by law in 1949. The Class D two-way communications service was opened in 1959. (CB also includes a Class A citizens band
and Class C remote control frequencies.)
FCC regulations permit only “transmissions” (one party to another) rather than
“broadcasts” (to a wide audience). Thus, advertising is not allowed on CB
Channels because that is “broadcasting.”
“Cuts Static coming in, adds Punch going out!”
Cobra proudly introduces the first Patent Pending technology that dramatically
improves the transmission and reception of CB radio signals.
This revolutionary system re c o n f i g u res the transmission signal which allows it to
be transferred more effectively through cluttered airwaves. It literally “punches”
your message through the hundreds of thousands of signals that are in the air. A t
the same time, S o u n d Tracker system dynamically adjusts the relationship between
the signal and static commonly re f e r red to as noise. This allows Cobra’s
S o u n d Tr a c k e r system to significantly reduce the amount of static on all incoming
CB signals. The system can be further optimized when two SoundTracker CB’s are
used to talk to each other.
The end result is a clearer, cleaner sounding reception of signals and more
powerful transmissions which dramatically improve CB Communications
All transmitter adjustments other than those supplied by the manufacture r
as front panel operating controls, must be made by, or under the supervision
of, the holder of an FCC-issued general Radio-Telephone Operator’s License.
Replacement or substitution of transistors, regular diodes or other parts of
a unique nature, with parts other than those recommended by Cobra, may
cause violation of the technical regulations of Part 95 of the FCC Rules, or
violation of Type Acceptance requirements of Part 2 of the Rules.
You should read and understand Part 95 (included with this unit) of the
FCC Rules and Regulations, before operating your Cobra radio, even
though the FCC no longer requires you to obtain an operators license.
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Specifications
FREQUENCY RANGE
The COBRA21 LTD ST transceiver represents one of the most advanced AM two-
way radios ever designed for use as a Class D station in the Citizens Radio
Service. This unit features advanced Phase Lock Loop (PLL) circuitry providing
complete coverage of all 40 channels as shown below.
Channel Channel Frequency Channel Channel Frequency
in MHz in MHz
1 26.965 21 27.215
2 26.975 22 27.225
3 26.985 23 27.255
4 27.005 24 27.235
5 27.015 25 27.245
6 27.025 26 27.265
7 27.035 27 27.275
8 27.055 28 27.285
9 27.065 29 27.295
10 27.075 30 27.305
11 27.085 31 27.315
12 27.105 32 27.325
13 27.115 33 27.335
14 27.125 34 27.345
15 27.135 35 27.355
16 27.155 36 27.365
17 27.165 37 27.375
18 27.175 38 27.385
19 27.185 39 27.395
20 27.205 40 27.405
The COBRA21 LTD ST has a vastly superior receiver which includes noise blanker
c i rcuitry and an automatic noise limiter. The receiver also features increased
p rotection against cross modulation and strong adjacent channel signals.
To obtain maximum performance please read carefully the descriptions and
operating instructions in this manual. Fill out below; keep for your records.
Serial No.
Date of Purchase
Dealer Name
Keep this manual for detailed information about your Cobra CB radio.
SAVE YOUR SALES RECEIPT, CARTON AND PACKING FOR POSSIBLE
FUTURE USE.
Specifications (cont.)
GENERAL
Channels 40
Frequency Range 26.965 to 27.405 MHz.
Frequency Control Phase Lock Loop (PLL) synthesizer.
Frequency Tolerance 0.005%.
Operating Temperature Range -30° C to + 50° C.
Microphone Plug-in dynamic.
Input Voltage 13.8VDC nom.(positive or negative ground).
Current Drain Transmit: AM full mod., 1.5A(maximum)
Receive: Squelched, 0.3A; full audio output, 1.2A
(nominal).
Size 53/4” W x 1 3/4” H x 7 1/2” D .
Weight 1.2 lbs.
Antenna Connector UHF, SO-239.
Semiconductors 26 transistors, 26 diodes, 4 integrated circuits.
Meter Illuminated; indicates relative power output and
received signal strength.
TRANSMITTER
Power Output 4 watts.
Modulation AM (Amplitude Modulation).
Frequency Response 300 to 3000 Hz.
Output Impedance 50 ohms, unbalanced.
RECEIVER
Sensitivity Less than 1 µV for 10dB (S+N)/N.
Selectivity 6dB @ 7 KHz, 60 dB @ 10 KHz.
Image Rejection 80 dB, typical.
Adjacent-Channel Rejection 60 dB, typical.
IF Frequencies Double Conversion: 1st: 10.695 MHz.
2nd: 455 KHz.
Automatic Gain Control (AGC) Less than 10 dB change in audio output for inputs
from 10 to 50,000 microvolts.
RF Gain Control Adjustable for optimum signal reception.
Noise Blanker RF type.
Squelch Adjustable; threshold less than 1µV.
Audio Output Power 4 watts.
Frequency Response 300 to 3000 Hz.
Distortion Less than 7% @ 3 watts @ 1000 Hz.
Built-in Speaker 16 ohms, round.
External Speaker (Not Supplied) 8 ohms; disables internal speaker when connected.
PA SYSTEM
Power Output 4 watts into external speaker.
External Speaker for PA 8 ohms, when PA-CB switch is in PA, the PAspeaker
(Not Supplied) also monitors the receiver; separate jack provided.
(SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE)
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Installation
Location
Plan the location of the transceiver and microphone bracket before starting the
installation. Select a location that is convenient for operation and does not interfere with the driver or passengers in the vehicle. In automobiles, the transceiver
is usually mounted to the underneath of the dash panel, with the microphone
bracket beside it.
Mounting and Connection
The transceiver is held in the universal mounting bracket by two thumbscrews,
permitting adjustment at the most convenient angle.
Auniversal mounting bracket is supplied along with self tapping screws and star
washers. The mounting must be mechanically strong and also provide a good
electrical connection to the chassis of the vehicle. To mount the transceiver:
1. Determine the most convenient location in your vehicle, hold the COBRA
radio with mounting bracket in the exact location desired. If nothing
will interfere with mounting it in the desired position, remove the
mounting bracket and use it as a template to mark the location for the
mounting screws.
2. Drill necessary holes and secure mounting bracket in location.
Installation (Cont.)
3. Connect the antenna cable plug to the standard receptacle on the unit. Most
CB antennas are terminated with a type PL-259 plug which mates with the
receptacle marked "ANT."
4. Connect the red lead of DC power cord to +13.8 VDC. In automobile instal-
lations, +13.8 VDC is usually obtained from the accessory contact in the fuse
box. This prevents the set being left on accidentally and also permits operating the unit without the vehicle's engine running.
Before installing the CB radio, visually check the vehicle battery connections to determine which battery terminal, positive or negative (positive is
the larger of the two) is grounded to the engine block (or chassis).
5.
Connect the black lead to the negative side of the automobile. This is usually
the chassis of the car. Any convenient location with good electrical contact
(remove paint) may be used. Plug power cable into jack on back of transceiver.
In positive ground automobiles the red wire goes to the chassis and the
black wire is connected to the ignition switch.
6. Mount microphone bracket on right side of the transceiver, or near it using
two screws supplied. When mounting in an automobile, place the bracket
under the dash so the microphone is readily accessible.
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