Cobra 25ltd St Cb Tranciever Manual

							OPERATING INSTRUCTIONS FOR YOUR
40 CHANNEL
CITIZENS BAND 
2-WAY MOBILE RADIO
Model
25 LTD ST
Cobra Electronics Corporation
6500 W. Cortland Street
Chicago, IL 60707
PRINTED IN HONG KONG ©COBRA ELECTRONICS CORP. 1997 480-205-P-001 
						

							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 commu-
nications service was opened in 1959. (CB also includes a Class Acitizens band
and Class C remote control frequencies.)
FCC regulations permit only ÒtransmissionsÓ (one party to another) rather than
ÒbroadcastsÓ (to a wide audience). Thus, advertising is not allowed on CB
Channels because that is Òbroadcasting.Ó
“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 reconfigures the transmission signal which allows it to
be transferred more effectively through cluttered airwaves. It literally ÒpunchesÓ
your message through the hundreds of thousands of signals that are in the air. At
the same time, SoundTracker system dynamically adjusts the relationship between
the signal and static commonly referred to as noise. This allows CobraÕs
SoundTrackersystem to significantly reduce the amount of static on all incoming
CB signals. The system can be further optimized when two SoundTracker CBÕs are
used to talk to each other.
The end result is a clearer, cleaner sounding reception of signals and more 
powerful transmissions which 
dramaticallyimprove CB Communications
All transmitter adjustments other than those supplied by the manufacturer
as front panel operating controls, must be made by, or under the supervision
of, the holder of an FCC-issued general Radio-Telephone OperatorÕs 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.
The CB Story
1
How To Use YourCitizens Band 
2-Way Mobile RadioModel 25 LTD ST
ContentsPage
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
AFew 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 
						

							Specifications (cont.)
GENERALChannels40 
Frequency Range26.965 to 27.405 MHz.
Frequency ControlPhase Lock Loop (PLL) synthesizer.
Frequency Tolerance0.005%.
Operating Temperature Range-30¡C to + 50¡C.
MicrophonePlug-in dynamic.
Input Voltage13.8VDC nom.(positive or negative ground).
Current DrainTransmit: AM full mod., 1.5A(maximum)
Receive: Squelched, 0.3A; full audio output, 1.2A
(nominal).
Size8 5
/
8Ó D  x 7 9
/
32Ó W  x 2 13
/
64Ó H .
Weight4 lbs.
Antenna ConnectorUHF, SO-239.
Semiconductors26 transistors, 26 diodes, 4 integrated  circuits.
Meter Illuminated; indicates relative power output and
received signal strength.TRANSMITTERPower Output4 watts. 
ModulationAM (Amplitude Modulation).
Frequency Response300 to 3000 Hz.
Output Impedance50 ohms, unbalanced.RECEIVERSensitivityLess than 1 µV for 10dB (S+N)/N.
Selectivity6dB @ 7 KHz, 60 dB @ 10 KHz. 
Image Rejection 80 dB, typical.
Adjacent-Channel Rejection60 dB, typical.
IF FrequenciesDouble 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 ControlAdjustable for optimum signal reception.
Noise BlankerRF type.
SquelchAdjustable; threshold less than 1µV.
Audio Output Power4 watts.
Frequency Response300 to 3000 Hz.
DistortionLess than 7% @ 3 watts @ 1000 Hz.
Built-in Speaker16 ohms, round.
External Speaker (Not Supplied)8 ohms; disables internal speaker when connected.PASYSTEMPower Output4 watts into external speaker.
External Speaker for PA8 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)
3
FREQUENCYRANGE
The COBRA25 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.
ChannelChannel FrequencyChannelChannel Frequency
in MHzin MHz
126.9652127.215
226.9752227.225
326.9852327.255
427.0052427.235
527.0152527.245
627.0252627.265
727.0352727.275
827.0552827.285
927.0652927.2951027.0753027.305
1127.0853127.315
1227.1053227.325
1327.1153327.335
1427.1253427.3451527.1353527.355
1627.1553627.365
1727.1653727.375
1827.1753827.385
1927.1853927.3952027.2054027.405
The COBRA25 LTD ST has a vastly superior receiver which includes noise blanker
circuitry and an automatic noise limiter. The receiver also features increased 
protection 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 PurchaseDealer Name
Keep this manual for detailed information about your Cobra CB radio.
SAVE YOUR SALES RECEIPT, CARTON AND PACKING FOR POSSIBLE
FUTURE  USE.
2
Specifications 
						

							5
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 oper-
ating the unit without the vehicles engine running.
Before installing the CB radio, visually check the vehicle battery connec-
tions 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 usuallythe 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.
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 inter-
fere 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.
4 
						

							7
Installation (Cont.)
Ignition Noise Interference
Use of a mobile receiver at low signal levels is normally limited by the presence
of electrical noise. The primary source of noise in automobile installations is from
the alternator and ignition system in the vehicle. Under most operating conditions,when signal level is adequate, the background noise does not present a seriousproblem. Also, when extremely low level signals are being received, the transceivermay be operated with vehicle engine turned off. The unit requires very little 
current and therefore will not significantly discharge the vehicle battery.
Even though the COBRA25 LTD ST has an automatic noise limiter, in some instal-
lations ignition interference may be high enough to make good communications
impossible. The electrical noise may come from several sources. Many possibili-
ties exist and variations between vehicles require different solutions to reduce the
noise. Consult your COBRAdealer or a 2-way radio technician for help in locat-
ing and correcting the source of severe noise.
Base Station Operation (Operation from 120VAC, House Current)
To operate your transceiver from your home or office, using the regular house
current as the power source, you will require a 12 VDC power pack that has been
specially designed for the purpose. It is available as optional equipment from
your COBRAdealer. It consists of a 120-volt, 60 Hz AC to 12-volt DC power con-
verter that delivers the required power for the operation of the transceiver. Simply
connect the red (+) and black ( - ) leads of the transceiver to the corresponding 
terminals of the power packs.
DO NOT ATTEMPT TO OPERATE THIS TRANSCEIVER BY
CONNECTING DIRECTLY TO 120 VAC.
Temporary Mobile Operation
To operate your COBRAtransceiver from a car on a temporary basis, you may
want to purchase an optional cigar lighter adapter from your COBRAdealer. This
adapter and a magnetic mount antenna allow you to quickly install your trans-
ceiver for temporary use.
6
CB Antenna
Since the maximum allowable power output of the transmitter is limited by the
FCC, the antenna is one important factor  affecting transmission distance. Only a
properly matched antenna system will allow maximum power transfer from the
50 ohm transmission line to the radiating element. In mobile installations (cars,
trucks, boats, etc.), an antenna system that is non-directional should be used.
Avertically polarized, quarter-wavelength whip antenna provides the most reli-
able operation and greatest range. Shorter, loaded-type whip antennas are more
attractive, compact and adequate for applications where the maximum possible
distance is not required. Also, the loaded whips do not present the problems of
height imposed by a full quarter-wavelength whip.
Mobile whip antennas utilize the metal body of the vehicle as a ground plane.
When mounted at a corner of the vehicle they are slightly directional, in the direc-
tion of the body of the vehicle. For all practical purposes, however, the radiation
pattern is nondirectional. The slight directional characteristic will be observed
only at extreme distances. Astandard antenna connector (type SO-239)is providedon the transceiver for easy connection to a standard PL259 cable termination.
Cobra loaded type antenna models are highly recommended for most installa-
tions. Consult your Cobra dealer for further details, or call 773-889-3087 and
speak to a Cobra customer representative.
When installed in a boat, the transceiver will not operate at maximum efficiency
without a ground plate, unless the vessel has a steel hull. Before installing the trans-
ceiver in a boat, consult your dealer for information regarding an adequate ground-
ing system and prevention of electrolysis between fittings in the hull and water.
3-Way Combination Antennas are available which allow operation of all three
bands (AM-FM & CB), using a single antenna. However, use of this type of
antenna usually results in less than normal transmit and receive range when
compared to a standard-type Single Band antenna designed for CB only. The
quality of reception of radio signals is highly dependent on the antenna sys-
tem. Call 773-889-3087 for further information.
Installation (Cont.) 
						

							Operation (Cont.)
9
5.
RF GAIN.Adjust as required to optimize signal. This control is used 
primarily to optimize reception in strong signal areas. Gain is reduced by
counterclockwise rotation of the control. 
6.CHANNELSELECTOR SWITCH.This switch selects any one of forty
Citizens Band channels desired. The selected channel is indicated by the
LED readout, directly above the channel selector knob.7.
S-METER. Swings proportionally to the strength of the incoming signal
during receiving.
RF-METER. Swings proportionally to the RF output power while 
transmitting.
8.CB-ANL/PASWITCH:Selects the mode of operation. In the CB-ANLpo-
sition, the PAfunction is disabled and the unit will transmit and receive
on the selected frequency. The PAfunction should not be used unless a PA
speaker is connected. In the PAmode, incoming CB transmissions will be
heard through the PAspeaker. This allows you to monitor messages when
you are not inside your vehicle. NOTE: ANL(Automatic Noise Limiter)
is a non-switchable feature that is always on to reduce 
background noise.9.NB-OFFSWITCH:When this switch is in the NB position, the RF noise
blanker is activated. The RF noise blanker is very effective for repetitive
impulse noise, such as ignition interference.10
.BRT/DIM SWITCH:Controls brightness of the LED channel indicator
and the multi-function meter, for optimum intensity for day or nighttime
driving.
11.
CH.19/CH.9/NORMALSWITCH. Used for instant selection of emer-
gency Channel 9 (CH. 9 position) or information Channel 19. In 
NORMALposition, all 40 CB channels can be accessed by the CHANNEL
SELECTOR switch.
12
.RX/TX LEDINDICATOR.When your radio is in the CB receive mode,
the LED will be green. When in transmit mode, the LED will be red. Controls and Indicators
Refer to controls, indicators and connectors as illustrated below:
A. Front Panel
1.
MICROPHONE CONNECTOR.Front panel microphone connector.
2.
OFF/ON/VOLUME.Turn clockwise to turn power on and set the desired
listening volume.
3.
SQUELCH.This control is used to cut off or eliminate receiver 
back-
ground noise in the absence of an incoming signal. For maximum receiver
sensitivity it is desired that the control be adjusted only to the point
where the receiver background noise or ambient background noise is
eliminated. Adjust until the receiver noise disappears. This will require
the incoming signal to be slightly stronger than the average receiver
noise. Further clockwise rotation will increase the threshold level which
a signal must overcome in order to be heard. Only strong signals will be
heard at a maximum clockwise setting.
4.
DYNAMIKE.Adjusts the microphone gain in the transmit and PA
modes. This controls the gain to the extent that full talk power is available
several inches away from the microphone. In the Public Address (PA)
mode, the control functions as the volume control.
Operation
8
10
11
7
14
15
13
12
1
2
3
4
5
6
8
9 
						

							11
3.
ANTENNACONNECTOR:This SO-239 connector permits connection
of the transmission line cable PL-259 connector to the transceiver.
4.
POWER. This jack permits connection of the DC power to the transceiver.Apower cord with polarized plug is supplied with the radio. The polar-
ized plug ensures that the power will always be connected properly.
Operating Procedure to Receive
1.
Be sure that the power cord, antenna and microphone  are connected to the
proper connectors before proceeding further. The PA/CB  should be in the
CB position.
2.
Turn the radio ON by rotating the VOLUME CONTROLclockwise.
3.
Set the RF GAIN CONTROLfully clockwise.
4.
Set DELTA-TUNE CONTROLto center(click-stop) position.
5.
Rotate SQUELCH CONTROLcounterclockwise until incoming signal is heard.
6.
Set the CHANNELSELECTORSwitch to the desired channel.
7.
Set VOLUME CONTROLto a comfortable listening level.
8.
Engage the SoundTracker system by depressing the button labeled ST. Listen to the background noise from the speaker. Turn the SQUELCH CON-
TROLslowly clockwise until the noise JUSTdisappears (no signal should be
present). Leave the control at this setting. The squelch is now properly adjust-
ed. The receiver will remain quiet until a signal is actually received. Do not
advance the control too far, or some of the weaker signals will not be heard.
The revolutionary SoundTracker system allows you to reduce unwanted
background noise (static) and increase the signal for better reception.
1
2
3
4
13.
SOUNDTRACKER™ INDICATOR.Ared LED will illuminate when the
SoundTracker system is engaged on your CB.
14.
SOUNDTRACKER™ SWITCH.Depressing this button turns on the
SoundTracker system in your CB.
15.
LED CHANNELDISPLAY.The selected channel will be displayed. 
B. Press-To-Talk Microphone
Both the receiver and transmitter are controlled by the Press-to-Talk switch on the
microphone. Press the switch and the transmitter is activated; release the switch
to receive. When transmitting, hold the microphone two inches from the mouth
and speak clearly in a normal voice. The microphone provided with your radio is
a detachable low-impedance dynamic type.
Operation (Cont.)Operation (Cont.)
10
C. Rear Panel
1.
PUBLIC ADDRESS:An external 8-ohm 4.0 watt PAspeaker may be con-
nected to the PASpeaker Jack when this unit is used as a public address
system. The speaker should be directed away from the microphone to
prevent acoustic feed-back. Physical separation or isolation of the micro-
phone and speaker must be employed when operating the PAat high 
output levels.
2.
EXTERNALSPEAKER:The External Speaker Jack is used for remote
receiver monitoring. The external speaker should have 8-ohm impedance
and be rated to handle at least 4.0 watts. When the external speaker is
plugged in, the internal speaker is automatically disconnected. 
						

							13 12
Operation (Cont.)Operating Procedure to Transmit
1.
Be sure the operator has read and understands part 95, F.C.C. Rules and
Regulations prior to operating the transmitter.
2.
Select the desired channel.
3.
Set the DYNAMIKE control fully clockwise.
4.
The receiver and transmitter are controlled by the pr
ess-to-talk switch
on the
microphone. Press the switch and the transmitter is activated; release switch
to receive. When transmitting (on a clear channel), hold the microphone two
inches from the mouth and speak clearly in a normal voice.
Be sure the antenna is properly connected to the radio before transmitting.
Prolonged transmitting without an antenna, or a poorly matched antenna,
could cause damage to the transmitter. 
Operating Procedure for Public Address
1.
Connect a PAspeaker to the PAjack provided on the rear panel.
2.
Place PA/CB/ANLswitch into the PAposition.
3.
Depress push-to-talk switch on micÑspeak in normal voice.
4.
Adjust PAspeaker volume with front panel DYNAMIKE control.
When the Volume control is rotated clockwise, activity on the CB channel will
be heard through the PAspeaker.
SOUNDTRACKER SYSTEMWhile previous systems only Òblanked outÓ or limited noise in higher sound
frequencies, the revolutionary new SoundTracker System actually reduces noise
while leaving the signal intact in the reception mode. In the transmission mode,
it actually strengthens the signal, providing you with a significant reduction in
noise on reception and transmission.Sound clarity is measured by the ratio of the signal level to the noise
level. The higher the signal-to-noise ratio, the better the sound.
HOW SOUNDTRACKER WORKSOn Reception–
“Cuts Noise Coming In”
With a normal CB, distant signals fall below the squelch level and are unintelli-
gible. With a SoundTracker CB, the noise level is cut by up to 90%, which
increases the signal-to-noise ratio and dramatically improves signal clarity. This
also allows you to significantly reduce the squelch level, which greatly expands
your listening range.On Transmission–
“Strengthens Signals Going Out”
ASoundTracker CB strengthens the transmit signal by more effectively using
the available RF power output of the CB. The result is improved transmission
signal clarity and an expanded transmission range.
How SoundTracker Works 
						

							1415
The COBRACB transceiver is specifically designed for the environment encoun-
tered in mobile installations. The use of all solid state circuitry and its light weight
result in high reliability. Should a failure occur, however, review the following,
then if necessary, replace parts only with identical parts. Do not substitute. Refer
to the schematic diagram and parts. 1.
Check connections to the source of power and make sure it is the 13.8 VDC
required to operate your radio.
2.
Check the fuse in the DC power cord. The main power lead (red wire) has a
2 Amp 3AG type fuse in its holder. Use only the above specified type and
size fuse for maximum protection. Failure to do so, will void the warranty.
3.
Make certain the microphone is properly plugged in.
4.
Make certain the antenna is properly connected and tuned for minimum
SWR. NOTE:COBRAantennas include full instructions as to how to tune
your antenna. If youre still in doubt about the procedure, contact the
COBRAdealer from whom you purchased your radio and antenna, for
advice. If you hired an installer to install your radio and antenna, contact the
installer.
If you are unable to correct the problem, refer the WARRANTYSERVICE
INSTRUCTIONS at the end of this manual for the correct procedure for warranty
and post-warranty service from COBRA.
Adjustment Warning
Replacement or substitution of certain parts with replacements other than those
recommended by COBRA, may be a violation of the technical regulations of Part
95 of the FCC Rules, or of Type Acceptance requirements of Part 2 of said rules.
When making adjustments other than transmitter adjustments, be sure to re-read
applicable portions of this instruction manual to make certain you are following
correct procedure and that the radio was properly installed, etc.
For technical assistance, please call our Automated Help Desk 
which can assist you by answering the most 
frequently asked questions about Cobra products.
(773) 889-3087
24 hours a day, 7 days a week.
AConsumer Service Representative can be reached through this same
number 8:00 am - 8:00 pm, Monday through Friday, CST.
Technical assistance is also available on-line in the Frequently Asked
Question (FAQ) section at www.cobraelec.com or by e-mail 
to [email protected]
Maintenance and Adjustment
Appendix
Citizens Band radio operators have largely adopted the Ò10-codeÓ for standard
questions and answers. Its use permits faster communications and better under-
standing in noisy areas. The following table lists some of the more common codes
and their meanings:
CodeMeaningCodeMeaning
10-1Receiving poorly10-35Confidential information
10-2Receiving well10-36Correct time is
10-3Stop transmitting10-37Wrecker needed at
10-4OK, message received10-38Ambulance needed at
10-5Relay message10-39Your message delivered
10-6Busy, stand by10-41Please turn to channel
10-7Out of service, leaving air10-42Traffic accident at
10-8In service, subject to call10-43Traffic Tie up at
10-9Repeat message10-44I have a message for you
10-10Transmission completed,10-45All units within range 
standing byplease report
10-11Talking too rapidly10-50Break channel
10-12Visitors present10-60
What is next message number?
10-13Advise Weather/Road10-62Unable to copy, use phone
conditions10-63Net directed to
10-16Make pick up at10-64Net clear
10-17Urgent business10-65Awaiting your next 
10-18Anything for us?message/assignment
10-19Nothing for you, return10-67All units copy
to base10-70Fire at
10-20My location is10-71Proceed with transmission
10-21Call by telephonein sequence
10-22Report in person to10-77Negative contact
10-23Stand by10-81Reserve hotel room for
10-24Completed last assignment10-82Reserve room for
10-25Can you contact10-84My telephone number is
10-26Disregard last information10-85My address is
10-27I am moving to channel10-91Talk closer to mike
10-28Identify your station10-93Check my frequency on 
10-29Time is up for contactthis channel
10-30Does not conform to FCC rules10-94Please give me a long count
10-32I will give you a radio check10-99Mission completed, all 
10-33EMERGENCYTRAFFICunits secure
10-34Trouble at this station10-200Police needed at 
						

							Appendix (Cont.)If You Think  You Need Service 
If  You Think  You Need Service, Call 773-889-3087