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Cobra 148 GTL ST Operating Instructions Manual

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Type: Operating Instructions
Category: Two-Way Radio
Pages: 15
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PRINTED IN THAILAND 

©COBRA ELECTRONICS CORPORATION 1997

480-241-P-001

Cobra Electronics Corporation

6500 W. Cortland Street

Chicago, IL 60707

OPERATING INSTRUCTIONS FOR YOUR

40 CHANNEL

CITIZENS BAND

SSB/AM 2-WAY

MOBILE RADIO

Model 148 GTL ST

148.GTL.ST.MANUAL  10/1/98 10:56 AM  Page 1

 


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40-CHANNEL, CITIZENS BAND 

SSB/AM 2-WAY MOBILE RADIO

Model 148 GTL ST

Contents

Page

The CB/SoundTracker Story ..............................................................1
Section I: Introduction......................................................................2
Section II: Specifications ..............................................................3, 4
Section III: Installation ........................................................5, 6, 7, 8
Section IV: Operation................................................................9 - 17
Controls and Indicators ....................................................................9
A.Control Functions..............................................................9, 10, 11
B.Indicator Functions ......................................................................12
Operating Procedure to Receive......................................................12
Operating Procedure to Transmit ....................................................13
Receiving SSB Signals ..............................................................13, 14
Alternate Microphones and Installation ..............................15, 16, 17
Section V: Maintenance and Adjustment ................................18 - 21
FCC Warning ..................................................................................18 
How SoundTracker Works ..............................................................19
Activating/Testing SoundTracker ......................................................20
Section VI: Appendix ..........................................................21, 22, 23
Ten Code ........................................................................................21
A few Rules That Should Be Obeyed ..............................................22
How Your CB Can Serve You ..........................................................22
Use Channel 9 for Emergency Messages Only ................................23
Warranty Service Instructions..........................................................24
Limited Two Year Warranty..............................................................25
Cobra CB Radio Accessories ..........................................................26

NOTICE:

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.
Citizens Band (CB) Radio operators are no longer required to obtain an FCC
license to operate their CB equipment  or provide station identification.
An operator of a CB radio station is required to comply with the communications
act and with the rules of CB Radio Operation.

The CB Story

1

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 communi-
cations 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 reconfigures the transmission signal wh i ch allows it to be
t ransferred  more  effectively  through  cluttered  airwaves.  It  literally  “punches”  yo u r
message through the hundreds of thousands of signals that are in the air. At the same
time, S o u n d Tra cker system dynamically adjusts the relationship between the signal
and static commonly referred to as noise. This allows Cobra ’s S o u n d Tra ck e r system to
significantly reduce the amount of static on all incoming CB signals. The system can
be further optimized when two SoundTra cker 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 manufacturer as
front panel operating controls, must be made by, or under the supervision of,
the holder of an FCC-issued general Radio-Telephone Opera t o r ’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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Section I Introduction

FREQUENCY RANGE
The COBRA 148 GTL ST transceiver represents one of the most advanced SSB/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, which is used
in the AM mode and in the upper and lower single sideband modes, providing
complete coverage of all 40 channels shown belo w.

Channel

Channel Frequency

in MHz

1

26.965

2

26.975

3

26.985

4

27.005

5

27.015

6

27.025

7

27.035

8

27.005

9

27.065

10

27.075

11

27.085

12

27.105

13

27.115

14

27.125

15

27.135

16

27.155

17

27.165

18

27.175

19

27.185

20

27.205

The COBRA 148 GTL ST has a vastly superior receiver which includes an RF gain
control and noise blanker circuitry effective in both AM and SSB modes., and an
automatic noise limiter effective in the AM mode. The receiver also features
increased protection against cross modulation and strong adjacent channel signals.
To obtain maximum performance please read carefully the descriptions and oper-
ating instructions in this manual.

Channel

Channel Frequency

in MHz

21

27.215

22

27.225

23

27.255

24

27.235

25

27.245

26

27.265

27

27.275

28

27.285

29

27.295

30

27.305

31

27.315

32

27.325

33

27.335

34

27.345

35

27.355

36

27.365

37

27.375

38

27.385

39

27.395

40

27.405

2

Serial No.

Date of Purchase

Dealer Name

Keep this manual for detailed information about your Cobra CB radio.
SAVE YOUR SALES RECEIPT, THE CARTON AND “PACKING”  MATERIALS FOR
POSSIBLE FUTURE USE.

3

Section II Specifications

GENERAL

Channels

40 AM, 40LSB, 40 USB.

Frequency Range

26.965 to 27.405 MHz.

Frequency Control

Phase Lock Loop (PLL) synthesizer.

Frequency Tolerance

0.005%

Frequency Stability

0.001%

Operating Temperature Range

-30° C to + 50° C

Microphone

Plug-in dynamic; with push-to-talk switch
and coiled cord.

Input Voltage

13.8V DC nominal, 15.9V max., 11.7V 
min. (positive or negative ground).

Current Drain

Transmit: AM full mod., 2.2A. SSB 12 watts 
PEP output, 2A. 
Receive: Squelched, 0.25A Maximum audio 
output, 0.6A.

Size

2 3/8”(H) x 7 7/8”(W) x 9 1/4”(D).

Weight

5 lbs.

Antenna Conductor

UHF, S0239.

Semiconductors

3 field effect transistors, 45 transistors, 63
diodes, 6 integrated circuits, 1 two color light
emitting diode.

Meter (3-in-1)

Illuminated; indicates relative output power,
received signal strength, and SWR.

TRANSMITTER
Power Output

AM, 4 watts. 
SSB, 12 watts, PEP.

Modulation

High-and low-level Class B, Amplitude 
Modulation.

Intermodulation Distortion

SSB: 3rd order, more than -25 dB.
5th order, more than -35 dB.

SSB Carrier Suppression

55 dB.

Unwanted Sideband

50 dB.

Frequency Response

AM and SSB; 300 to 2500 Hz.

Output Impedance

50 ohms, unbalanced

Output Indicators

Meter shows relative RF output power 
and SWR. Transmit LED glows red when 
transmitter is in operation.

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Section II Specifications (Cont.)

4

RECEIVER

Sensitivity

SSB: 0.25 µV for 10dB (S+N)/N at greater
than 1/2-watt of audio output. 
AM: 0.5 µV for 10 dB (S+N)/ at greater 
than 1/2-watt of audio output.

Selectivity

AM: 6dB @ 3 KHz, 50 dB @ 9 KHz. 
SSB: 6 dB @ 1.1 KHz, 60 dB @ 2.3 KHz.

Image Rejection

More than 65 dB.

IF Frequency

AM: 7.8 MHz 1st IF, 455 KHz 2nd IF.
SSB: 7.8 MHz.

Adjacent-Channel Rejection

60 dB AM & 70 dB SSB.

AM and SSB RF Gain Control

40 dB adjustable for optimum signal 
reception.

Automatic Gain Control (AGC)

Less than 10 dB change in audio 
output for inputs from 10 to 100,000 microvolts.

Squelch

Adjustable; threshold less than 0.25 µV.

ANL

Switchable.

Noise Blanker

RF type, effective on AM and SSB.

Voice Lock Range

±2.5 KHz.

Audio Output Power

4 watts into 8 ohms.

Frequency Response

300 to 2500 Hz.

Built-in Speaker

4 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
(Not Supplied)

8 ohms.

(SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE)

5

Section III Installation

LOCATION

Plan the location of the transceiver and microphone bracket before starting the in-
stallation. 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 usu-
ally mounted below the dash panel, with the microphone bracket beside it.

MOUNTING THE CONNECTION

The COBRA 148 GTL ST is supplied with a universal mounting bracket. When
mounting the bracket and radio to your car, make sure it is mechanically strong.
Also provide a good electrical connection to the chassis of the vehicle. Proceed as
follows to mount the transceiver:

1. After you have determined the most convenient location in your vehicle, hold

the COBRA 148 GTL ST with mounting bracket in the exact location desired. If
nothing will interfere with mounting it in the desired position, remove the
mounting bolts. Before drilling the holes, make sure nothing will interfere with
the installation of the mounting bolts.

2. Connect the antenna cable plug to the standard receptacle on the rear panel.

Most CB antennas are terminated with a  type PL-259 plug and mate with the
receptacle.

3. Connect the red DC power input wire (with the fuse) to +13.8V DC. This wire

extends from the rear panel. In automobile installation, +13.8V DC is usually
obtained from the accessory contact on the ignition switch. This prevents the
set being left on accidentally when the driver leaves the car and also permits
operating the unit without the engine running. Locate the accessory contact on
most ignition switches by tracing the power wire from the AM broadcast receiv-
er in the car.

4. Connect the black lead to -13.8V DC. This is usually the chassis of the car. Any

convenient location with good electrical contact (remove paint) may be used.

5. Mount the microphone bracket on either side of the transceiver, using the two

screws supplied. When mounting in an automobile, place the bracket under the
dash so the microphone is readily accessible.

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6

Section III Installation

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 generator and ignition system in the vehicle. Under most operating conditions,
when signal level is adequate, the background noise does not present a serious
problem. Also, when extremely low level signals are being received, the transceiv-
er may 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 COBRA 148 GTL ST has ANL and NB controls, in some installa-
tions ignition interference may be high enough to make good communications
impossible. The electrical noise may come from several sources. Many possibilities
exist and variations between vehicles require different solutions to reduce the
noise. Consult your COBRA dealer or a 2-way radio technician for help in locat-
ing and correcting the source of severe noise.

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.
A vertically polarized, quarter-wavelength whip antenna provides the most reliable
operation and greatest range. Shorter, loaded-type whip antennas are more attrac-
tive, compact and adequate for applications where the maximum possible dis-
tance 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
direction of the body of the vehicle. For all practical purposes, however, the radia -
tion pattern is nondirectional. The slight directional characteristic will be observed
only at extreme distances. A standard antenna connector (type SO239) is provided
on the transceiver for easy connection to a standard PL 259 cable termination.
If the transceiver is not mounted on a metal surface, it is necessary to run a sepa-
rate ground wire from the unit to a good metal electrical ground in the vehicle.
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 transceiver in a boat, consult your dealer for information re-
garding an adequate grounding system and prevention of electrolysis between fit-
tings in the hull and water.

7

Section III Installation (Continued)

TUNING THE ANTENNA FOR OPTIMUM SWR

Since there is such a wide variety of base and mobile antennas, this section will
strictly concern itself to the various types of mobile adjustable antennas.
Because antenna length is directly related to the channel frequency, it must be
tuned to resonate optimally all 40 channels of the transceiver. Channel 1 requires
a longer antenna than Channel 40 because it is a lower frequency.
Due to the various methods of adjusting antennas for proper SWR we have chosen
what we think is the optimum method:
A. Antennas with adjustable screws (set screws).

1. Start with the antenna extended and tighten the set screw lightly enough so

that the antenna can be lightly tapped with your finger for easy adjustment.

2. Set your COBRA 148 GTL ST to Channel 21. Press the PTT (Push-to-Talk)

switch, and tap the antenna (making it shorter). The SWR meter will show a
lower reading each time the antenna is tapped. By continuing to shorten the
antenna you will notice the SWR reading will reach a low point and then
start rising again. This means that you have passed the optimum point for
Channel 21. Extend the antenna a short distance and again follow the 
procedure above.
When the lowest point has been reached, switch to Channel 1 and then to
Channel 40 and compare SWR readings. They should be almost equal.

B. Antennas  which must be cut to proper length.

1. Follow the same procedure as above, but adjust the length by cutting in 1/8”

increments until a good match is obtained.

2. Be very careful not to cut too much at one time, as once it is cut, it can no

longer be lengthed.

3. The whip is easily cut by filing a notch all the way around and breaking the

piece off with a pliers.

NOTE

THE PROPER SETTING IS ACHIEVED WHEN THE SWR IS 
1.5 OR BELOW, AND WHEN IT HAS THE SAME READING 
FOR CHANNELS 1 AND 40.

If you are having difficulties in adjusting your antenna, check the following:

A. All doors must be closed when adjusting the antenna.

B. Make sure the antenna base is grounded.

C. C h e ck your coaxial cable routing (it may be pinched when routed into the car).

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Section III Installation (Continued)

D. Try a different location on your car (keeping in mind the radiation pattern 

you wish).

E.

Is the antenna perfectly vertical?

F.

Try a different location in your neighborhood. Stay away from large metal
objects when adjusting (metal telephone or light posts, fences, etc.).

NOTE

The COBRA 148 GTL ST will operate into an SWR of 2 to 1 indefinitely
and sustain an SWR of 20:1 for a maximum of 5 minutes at rated 
operating conditions.

EXTERNAL SPEAKER

The external speaker jack (EXT. SPK.) on the rear panel is used for remote receiver
monitoring. The external speaker should have 8 ohms impedance and be able to
handle at least 4 watts. When the external speaker is plugged in, the internal
speaker is disconnected.

PUBLIC ADDRESS

To use the transceiver as a public address system connect an external 8 ohm
speaker (4 watts minimum) to the PA SPK. jack located on the rear panel. Direct
speaker away from the microphone to prevent acoustic feedback. Physical separa-
tion or isolation of the microphone and speaker is important when operating the
PA at high output levels.

8

9

Section IV Operation

CONTROLS AND INDICATORS

There are fourteen controls and four indicators on the front panel of your COBRA
148 GTL ST.

A. CONTROL FUNCTIONS

1. OFF/ON/VOLUME (inner concentric dial). Turn clockwise to apply power to

the unit and to set the desired listening level. During normal CB operation,
the VOLUME control is used to adjust the output level obtained either at the
transceiver speaker or the external speaker, if used.

2. SQUELCH (outer concentric dial). This control is used to cut off or eliminate

receiver background noise in the absence of an incoming signal. For maxi-
mum 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. Turn fully counterclockwise then slowly clockwise until the receiv-
er noise disappears. Any signal to be recei ved must now be slightly stronger
than the average received 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.

3. RF GAIN CONTROL (inner concentric dial). Used to reduce the gain of the

RF amplifier under strong signal conditions.

1

2

3

5

6

4

7

8

9

21

10

11

12

13

15

16

17

18

14

19 20

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Section IV Operation (Continued)

4.

SWR CAL CONTROL (outer concentric dial). In order for you to achiev e
maximum radiated power and the longest range, it is important that your
antenna be in good condition, properly adjusted and matched to your trans-
ceiver. The Built-in SWR (standing wave ratio) meter lets you easily measure
your antenna condition. To operate this function, connect your antenna to the
transceiver antenna output connector. Select a channel near the middle of the
band such as 21 or the channel you plan to use most frequently. Turn the
power on and set the meter function switch to the CAL position. Press and
hold the microphone push-to-talk button and using the SWR CAL control,
adjust the meter to read the CAL position indicated on the meter face. Then,
without releasing the microphone button, switch the meter function switch to
the SWR position and read the SWR indicated. The lower the figure, the bet-
ter, with 1 being ideal. Generally speaking, readings up to 3 are acceptable,
but over 3 indicates that you are losing radiated power and antenna adjust-
ment may be advisable.

5.

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.

6.

VOICELOCK. Allows variation of the receiver operating frequencies above
and below the assigned frequency. Although this control is intended primarily
to tune in SSB signals, it may also be used to optimize AM signals as
described in the Operating Procedure paragraphs.

7.

DIM/NOR/BRT SWITCH. Controls the brightness of the meter and LED chan-
nel indicator for optimum intensity for day or night-time driving.

8.

CHANNEL SELECTOR. This switch selects any one of the forty Citizens Band
or 80 single side band channels desired. The selected channel appears on the
LED readout directly above the Channel Selector knob. Channel 9 has been
reserved by the FCC for emergency communications involving the immediate
safety of life of individuals or immediate protection of property. Channel 9
may also be used to render assistance to a motorist.

9.

0FF/ANL-NB/ANL SWITCH. In the ANL position only the automatic 
noise limiter in the audio circuits is activated. When the switch is placed 
in the ANL + NB position, the RF noise blanker also is activated. The 
RF noise blanker is very effective for repetitive impulse noise such as 
ignition interference.

10

Section IV Operation (Continued)

10. PA/CB SWITCH. Selects the mode of operation. In the CB position, the PA func-

tion is disabled and the unit will transmit and receive on the speaker that is con-
nected. In the PA mode, incoming CB transmission will be heard through the PA
s p e a k e r. This allows you to monitor messages while outside of your ve h i c l e .
To use the PA feature, a speaker having a voice coil impedance of 8 ohms and
a power handling capability of at least three watts should be used. This speak-
er must be plugged into the PA SPKR jack at the rear of the tra n s c e ive r. If the
public address feature is to be used primarily for outdoor applications, the use
of a weatherproof horn type public address speaker is recommended. Th e
d u rability of this type speaker plus the inherent efficiency of such a speaker
will provide more than adequate results when combined with the high audio
output level available from the COBRA 148 GTL ST. With the PA speaker con-
nected as outlined previously, be sure that there is physical separa t i o n
between the microphone and the speaker itself. If the speaker is located too
close to the microphone, acoustic feedback will result when the public
address system is operated at high volume. A directional type outdoor speaker
reduces the amount of isolation required. Some experimentation will deter-
mine the minimum amount of isolation required for a given sound level from
the public address system.

NOTE

PA volume is controlled by adjusting the DYNAMIKE knob to
the desired volume.

11. S - R F / CAL/SWR SWITCH. When in the S-RF position, the meter swings propor-

tionally to the strength of the received signal. When transmitting, the meter
indicates relative RF output pow e r.

When in the “CA L” position, the SWR meter can be calibrated by adjusting the
“SWR” control to the “CA L” mark on the meter face.

When in “SWR” position, the standing wave ratio is measured.

12. MODE (USB/AM/LSB) SWITCH. This sw i t ch is used to select AM, LSB or USB

mode of operation. Unless the station with wh i ch communication is desired is
equipped with SSB, the AM mode is normally used. The mode selector sw i t ch
changes the mode of operation of both transmitter and receiver simultaneous-
l y. Turn to “Receiving SSB signals” for a further explanation of single sideband.

13. TONE SWITCH HI/NOR/LOW. This switch is used to shape the audio

response to the operator’s preference. Bass is increased in the LOW position
and treble is increased in the HI position.

14. SOUNDTRACKER

SWITCH. Depressing this button turns on the SoundTracker

system in your CB.

11

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12

Section IV Operation (Continued)

B. INDICATOR FUNCTIONS

15. S-METER. Swings proportionally to the strength of the incoming signal.
16. RF METER. Swings proportionally to the RF output power.
17. SWR METER. Swings proportionally to the ratio of standing wave voltage and RF

output. Used to properly adjusts the length of the antenna, and to monitor the qual-
ity of the coaxial cable and all RF electrical connections. If there is any degra d a t i o n
wh a t s o e ver in any of the above, due to humidity, salt, spray, vibration or corrosion,
the SWR meter reading will rise, thereby indicating that a problem exists.
To calibrate, sw i t ch to the “CA L” position, transmit in AM Mode by pressing the (PTT)
mic sw i t ch, and adjust the SWR control to the “CA L” mark on the meter then sw i t ch
to “SWR” position for the SWR measurement (Note: CB must be in AM mode).

18. CHANNEL INDICATOR. Numbered LED indicates the selected channel you

wish to operate on.

19. RECEIVE/TRANSMIT INDICATOR. The receiver/transmit LED indicator is

located next to the channel indicator. When in receive, the LED will be
green. When in transmit the LED will be red.

20. S O U N D T R ACKER™  INDICATO R . A  red  LED  will  illuminate  when  the

SoundTracker system is engaged on your CB.

21. PRESS-TO-TALK MICROPHONE. 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 radio comes complete with low-impedance (500 ohm) dynamic
microphone. For installation instructions on the other microphones see
ALTERNATE MICROPHONES AND INSTALLATION section.

OPERATING PROCEDURE TO RECEIVE

1.

Be sure that the power source, microphone and antenna are connected to the
proper connectors before going to the next step.

2.

Set PA-CB Switch to the CB position and turn unit on by turning VOL control
clockwise on COBRA 148 GTL ST.

3.

Set the VOLUME for a comfortable listening level.

4.

Set MODE switch to the desired mode.

5.

Set the RF gain control fully clockwise for maximum RF gain.

6.

Listen to the background noise from the speaker. Turn the SQUELCH control
slowly clockwise until the noise JUST disappears (no signal should be pre-
sent). 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.

7.

Set the CHANNEL selector switch to the desired channel.

8.

Adjust the VOICE LOCK control to clarify the SSB signals or to optimize 
AM signals.

13

Section IV Operation (Continued)

OPERATING PROCEDURE TO TRANSMIT

1.

Select the desired channel of transmission.

2.

Set the DYNAMIKE control fully clockwise.

3.

If the channel is clear, depress the Push-To-Talk switch on the microphone
and speak in a normal voice.

RECEIVING SSB SIGNALS

There are three types of signals presently used for communications in the Citizens
Band: AM, USB, and LSB. When the MODE switch on your unit is placed in the
AM position, only standard double-sideband, full carrier signals will be detected.
An SSB signal may be recognized while in the AM mode by its characteristic
“Donald Duck” sound and the inability of the AM detector to produce an intelligi-
ble output. The USB and LSB modes will detect upper sideband and lower side-
band respectively, and standard AM signals.

SSB reception differs from standard AM reception in that SSB receiver does not
require a carrier or opposite sideband to produce an intelligible signal. A single-
sideband transmitted signal consists only of the upper or the lower sideband and
no carrier is transmitted. The elimination of the carrier from the AM signal helps to
eliminate the biggest cause of whistles and tones heard on channels which make
even moderately strong AM signals unreadable. Also, SSB takes only half of an AM
channel, therefore two SSB conversations will fit into each channel expanding the
40 AM channels to 80 SSB channels. The reduction in channel space required also
helps in the receiver because only half of the noise and interference can be
received with 100% of the SSB signal.

An SSB signal may be received only when the listening  receiver is functioning in
the same mode. In other words, an upper sideband signal (USB) may be made
intelligible only if the receiver is functioning in the USB position.

If a lower sideband (LSB) signal is heard when the receiver is in the USB  mode,
no amount  of tuning will make the signal intelligible. The reason for this may be
understood if you consider that  when the modulation is applied to the transmit-
ter’s microphone in the USB mode, the transmitter’s output frequency is increased
whereas in the LSB mode the transmitter’s output frequency is decreased. The
result in listening to the receiver is that when the MODE switch is in the proper
position (either USB or LSB), a true reproduction of single tone of modulation will
result, and if the tone is increased in frequency (such as a low-pitched whistle or a
high-pitched whistle) you will hear the increase in the output tone of the receiver.
If the incorrect mode is selected, an increase in tone of a whistle applied to the
transmitter will cause a decrease in the resultant tone from the receiver.

148.GTL.ST.MANUAL  10/1/98 10:56 AM  Page 15

 


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14

Section IV Operation (Continued)

Thus when a voice is used in place of a whistle or tone, in the proper listening
mode the voice will be received correctly whereas in the incorrect mode, the
voice will be translated backwards and cannot be made intelligible by the voice
lock control. When listening to an AM transmission, a correct sideband is heard in
either mode since both upper and lower sideband are received.

Once the desired SSB mode has been selected, frequency adjustment may be nec-
essary in order to make the incoming signal intelligible, the VOICE LOCK control
allows the operator to vary frequency above and below the exact-center frequency
of the received signal. If the sound of the incoming signal is high or low pitched,
adjust the operation of the VOICE LOCK. Consider it as performing the same func-
tion as a phonograph speed control. When the speed is set too high, voices will be
high-pitched and if set too low, voices will be low-pitched. Also, there is only one
correct speed that will make a particular record produce the same sound that was
recorded. If the record is played on a turntable that rotates in the wrong direction
(opposite sideband) no amount of speed control (VOICE LOCK) will produce an
intelligible sound.

An AM signal received while listening in one of the SSB modes will produce a
steady tone (carrier) in addition to the intelligence, unless the SSB receiver is tuned
to exactly the same frequency by the VOICE LOCK control. For simplicity it is rec-
ommended that the AM modes be used to listen to AM signals.

15

Section IV Operation (Continued)

ALTERNATE MICROPHONES AND INSTALLATION

For best results, the user should select a low-impedance dynamic type micro-
phone or a transistorized microphone. Transistorized type microphones have a low
output impedance characteristic. The microphones must be provided with a 4-lead
cable. The audio conductor and its shielded lead comprise two of the leads. The
third lead is for receive control, the forth is for transmit control.
The microphone should provide the functions shown in schematic below.

4 WIRE MIC CABLE

Pin Number

Mic Cable Lead

1

Grounding

2

Audio Lead

3

Transmit Control

4

Receive Control

Fig. 1. Cobra 148 GTL ST microphone schematic.

If the microphone to be used is provided with pre-cut leads, they must be revised
as follows.

1.

Cut leads so that they extend 7/16” beyond the plastic insulating jacket of the
microphone cable (see Fig. 2.)

2.

All leads should be cut to the same length. Strip the ends of each wire 1/8”
and tin the exposed wire.

Before beginning the actual wiring, read carefully, the circuit and wiring informa-
tion provided with the microphone you select. Use the minimum head required in
soldering the connections. Keep the exposed wire lengths to a minimum to avoid
shorting when the microphone plug is reassembled.

148.GTL.ST.MANUAL  10/1/98 10:56 AM  Page 17

 


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16

3

4

2

1

Section IV Operation (Continued)

Fig. 2. Microphone Cable Preparation

To wire the microphone cable to the plug provided, proceed as follows.

Fig. 3. Microphone plug wiring.

1.

Remove the retaining screw.

2.

Unscrew the housing from the pin receptacle body.

3.

Loosen the two cable clamp retainer screws.

4.

Feed the microphone cable through the housing, knurled ring and washer as
shown Fig. 3B.

5.

The wires must now be soldered to the pins as indicated in the above wiring
tables. If a vise or clamping tool is available it should be used to hold the pin
receptacle body during the soldering operation, so that both hands are free to
perform the soldering. If a vise or clamping tool  is not available, the pin recep-
tacle body can be held in a stationary position by inserting it into the micro-
phone jack on the front panel. The numbers of the pins of the microphone plug
are shown in Fig 4, as viewed from the back of the plug. Before soldering the
wire to the pins, pre-tin the wire receptacle of each pin of the plug.

17

Section IV Operation (Continued)

Fig. 4. Microphone plug pin numbers viewed from rear of pin receptacle.

Be sure that the housing and the knurled ring of Fig. 3 are pushed back onto the
microphone cable before starting to solder. If the washer is not captive to the pin
receptacle body, make sure that it is  placed on the threaded portion of the pin
receptacle body before soldering.

If the microphone jack is used to hold the pin receptacle during soldering opera-
tion, best results are obtained when the connections to pins 1 and 3 are made first
and then the connections to pins 2 and 4. Use a minimum amount of solder and
be careful to prevent excessive solder accumulation on pins, which could cause a
short between the pin and the microphone plug housing.

6.

When all soldering connections to the pins of the microphone are com-
plete, push the knurled ring and the housing forward and screw the housing
onto the threaded portion of the pin receptacle body. Note the location of
the screw clearance hole in the plug housing with respect to the threaded
hole in the pin receptacle body. When the housing is completely threaded
into the pin receptacle body, a final fraction of a turn either clockwise or
counterclockwise may be required to align the screw hole with the threaded
hole in the pin receptacle body. When these are aligned, the retaining screw
is then screwed into place to secure the housing to the pin receptacle body.

7.

The two cable clamp retainer screws should now be tightened to secure the
housing to the microphone cord. If the cutting directions have been careful-
ly followed, the cable clamp should secure to the insulation jacket of the
microphone cable.

8.

Upon completion of the microphone plug wiring, connect and secure the
microphone plug in the transceiver.

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18

Section V Maintenance and Adjustment

The COBRA 148 GTL ST transceiver is specifically designed for the environment
encountered in mobile installations. The use of all solid state circuitry and its light
weight result in high reliability. Should a failure occur, however, replace parts
only with identical parts. Do not substitute. Refer to the schematic diagram and
parts list.

NOTE

If the performance described in the OPERATION and MAINTENANCE 
AND ADJUSTMENT sections is not obtained, review the operating 
instructions to insure that proper procedures were followed. If a problem
still exists, refer to WARRANTY SERVICE INSTRUCTIONS elsewhere in 
this manual.

FCC WARNING

Replacement or substitution of transistors, regular diodes or other parts of
a unique nature, with parts other than those recommended by Cobra ,
m ay cause violation of the technical regulations of Part 95 of the FCC
Rules, or violation of Type Acceptance requirements of Part 2 of the
R u l e s .
Citizens Band (CB) Radio operators are no longer required to obtain an
FCC license to operate their CB equipment or provide station identification.

N e vertheless, an operator of a CB radio station is still required to comply

with the communications act and with the rules of CB Radio Opera t i o n .

How SoundTracker Works

SOUNDTRACKER SYSTEM

While previous systems only “blanked out” or limited noise in higher sound fre-
quencies, 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 WORKS
On Reception–

Cuts Noise Coming In”

With a normal CB, distant signals fall below the squelch level and are unintelligi-
ble. With a SoundTracker CB, the noise level is cut by up to 90%, which increas-
es 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 Tra n s m i s s i o n –

S t rengthens Signals Going Out”

A SoundTracker 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.

19

148.GTL.ST.MANUAL  10/1/98 10:56 AM  Page 21

 


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Activating/Testing SoundTracker 

ACTIVATING SOUNDTRACKER

1. Press the SoundTracker 

button on the right 
side of front panel.

TESTING SOUNDTRACKER

1. Select any unused channel on your CB.

2. Open the squelch fully by turning the knob

counter-clockwise until it stops.

3. Turn the volume up louder than your nor-

mal listening level.

4. Switch the SoundTracker toggle off 

and on. Notice the significant
reduction in noise.

20

21

Section VI Appendix

Citizens Band radio operators have largely adopted the “10-code” 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.

10 CODE

Code

Meaning

Code

Meaning

10-1

Receiving poorly

10-2

Receiving well

10-3

Stop transmitting

10-4

OK, message received

10-5

Relay message

10-6

Busy, stand by

10-7

Out of service, leaving air

10-8

In service, subject to call

10-9

Repeat message

10-10 Transmission completed, 

standing by

10-11 Talking too rapidly
10-12 Visitors present
10-13 Advise Weather/Road condi-

tions

10-16 Make pick up at
10-17 Urgent business
10-18 Anything for us?
10-19 Nothing for you, return to

base

10-20 My location is
10-21 Call by telephone
10-22 Report in person to
10-23 Stand by
10-24 Completed last assignment
10-25 Can you contact
10-26 Disregard last information
10-27 I am moving to channel
10-28 Identify your station

10-29 Time is up for contact
10-30 Does not conform to FCC rules
10-32 I will give you a radio check
10-33 EMERGENCY TRAFFIC
10-34 Trouble at this station
10-35 Confidential information

10-36

Correct time is

10-37

Wrecker needed at

10-38

Ambulance needed at

10-39

Your message delivered

10-41

Please turn to channel

10-42

Traffic accident at

10-43

Traffic Tie up at

10-44

I have a message for you

10-45

All units within range 
please report

10-50

Break channel

10-60

What is the next message 
number?

10-62

Unable to copy, use phone

10-63

Net directed to

10-64

Net clear

10-65

Awaiting your next 
message/assignment

10-67

All units copy

10-70

Fire at

10-71

Proceed with transmission
sequence

10-77

Negative contact

10-81

Reserve hotel room for

10-82

Reserve room for

10-84

My telephone number is

10-85

My address is

10-91

Talk closer to mike

10-93

Check my frequency on 
this channel

10-94

Please give me a long 
count

10-99

Mission completed, all 
units secure

10-200

Police needed at

148.GTL.ST.MANUAL  10/1/98 10:56 AM  Page 23

 


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22

Section VI Appendix (Continued)

A FEW RULES THAT SHOULD BE OBEYED

1.

You are not allowed to carry on a conversation with another station for more
than five minutes at a time without taking a one-minute break, to give others
a chance to use the channel.

2.

You are not allowed to blast others off the air by over-powering them with
illegally amplified transmitter power, or illegally high antennas.

3.

You can’t use the CB to promote illegal activities.

4.

You are not allowed to use profanity.

5.

You may not play music in your CB.

6.

You may not use your CB to sell merchandise or professional service.

HOW YOUR CB CAN SERVE YOU

Warn of traffic tie ups ahead.

Provide weather and road information.

Provide help fast in event of emergency or breakdown.

Suggest good spots to eat and sleep.

Make long trips more interesting, and help keep you awake.

Provide direct contact with your office or home.

Make friends for you as you travel.

Provide “local information” to find your destination.

Help law enforcement officers by reporting drunk and reckless drivers.

Section VI Appendix (Continued)

23

USE CHANNEL 9 FOR EMERGENCY MESSAGES ONLY

FCC gives the following examples of permitted and prohibited types of communi-
cations for use on Channel 9. These are guidelines and are not intended to be all-
inclusive.

Permitted

Example Message

Yes

”A tornado sighted six miles north of town.”

No

”This is observation post number 10. No tornado sighted.”

Yes

”I am out of gas on Interstate 95.”

No

”I am out of gas in my driveway.”

Yes

There is a four-car collision at Exit 10 on the Beltway, send 

police and ambulance.”

No

”Traffic is moving smoothly on the Beltway.”

Yes

”Base to Unit 1, the Weather Bureau has just issued a thun-

der storm warning. Bring the sailboat into port.”

No

”Attention all motorists. The Weather Bureau advises that the

snow tomorrow will accumulate 4 to 6 inches.”

Yes

“There is a fire in the building on the corner of 6th and 

Main Streets.”

No

“This is Halloween patrol unit number 3. Everything is 

quiet here.“ 

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If You Think You Need Service

If You Think You Need Service, Call 773-889-3087

You may be asked to send your unit to the Cobra factory. It will be  necessary to
furnish the following,  in order to have the product serviced and re t u r n e d .

1 . For Wa r ranty Repair,  include some form of pro o f - o f - p u rchase, such as  a me-

chanical  re p roduction  or  carbon  or  a  sales  receipt.  If  you  send  the  original
receipt it cannot be re t u r n e d .

2 . Send the entire product. Must include CB unit and micro p h o n e .
3 . Enclose  a  description  of  what  is  happening  with  the unit.  Include  a  typed  or

c l e a r ly printed name and address of wh e re the unit is to be  re t u r n e d .

4 . Pa ck unit secure ly to prevent damage in transit. If possible, use the original pack-

ing  material.

5 . S h i p prepaid and insured by way of a traceable carrier  (to  avoid  loss in tra n s i t )

s u ch as United Pa rcel Service (UPS), Roadway Pa rcel Service (RPS) or First Class
Insured Mail to C o b ra  Factory  Service,  Cobra Electronics Corporation, 6500 W.
Cortland St., Chicago, IL 60707. Cobra is not responsible for units not received if
p a ckage has not been properly insured.

6 . If the unit is in wa r ra n t y, upon receipt of your unit it will either be re p a i red or

ex changed depending on the model. Please allow  approx i m a t e ly 3 to 4 we e k s
b e f o re contacting us for status. If the unit is out of wa r ranty a letter will auto-
m a t i c a l ly be sent informing you of the repair charge or replacement charge. If
you have any questions, please call  773-889-3087 for assistance.

24

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.

A Consumer Service Representative can be reached through this same num-

ber 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 productinfo@cobraelec.com

25

LIMITED TWO YEAR WARRANTY

COBRA ELECTRONICS CORPORATION warrants that its COBRA CB Radios, and
the component parts thereof, will be free of defects in workmanship and materials
for period of two (2) years from the date of first consumer purchase. This warranty
may be enforced by the first consumer purchaser, provided that the product is uti-
lized within the U.S.A.
COBRA will, without charge, repair or replace, at its option, defective CB radios,
products  or  component  parts  upon  delivery  to  the  COBRA  factory  Service
Department, accompanied by proof of the date of first consumer purchase, such as
a duplicated copy of a sales receipt.
You must pay any initial shipping charges required to ship the product for warranty
service, but the return charges will be at Cobra's expense, if the product is repaired
or replaced under warranty. For further details concerning procedures for obtaining
service, see the “If You Think You Need Service” section of the Owner’s Manual.
Exclusions: This limited warranty does not apply; 1) to any product damaged by
accident; 2) in the event of misuse or abuse of the product or as a result of unautho-
rized alterations or repairs; 3) if the serial number has been altered, defaced or re-
moved; 4) if the owner of the product resides outside the U.S.A. 
All implied warranties, including warranties of merchantability and fitness for a
particular purpose are limited in duration to the length of this warranty.
COBRA shall not be liable for any incidental, consequential or other damag-
es; including, without limitation, damages resulting from loss of use or cost of
i n s t a l l a t i o n .
Some states do not allow limitations on how long an implied warranty lasts and/or
do not allow the exclusion or limitation of incidental or consequential damages, so
the above limitations may not apply to you.

COBRA ELECTRONICS CORPORATION

6500 W. Cortland Street

Chicago, Illinois 60707

148.GTL.ST.MANUAL  10/1/98 10:56 AM  Page 27

 


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Description

Part No.          Cost Ea.  X  Qty.  =   Amount

Replacement microphone with 4-pin connector 
for 148 GTL ST

CA-73

$19.95

MOBILE POWER MICROPHONE
Amplified Power Microphone with 4-pin connector 
for 148 GTL ST

CA-75

$19.95

NOISE CANCEL MICROPHONE for 148 GTL ST

CA-77

$39.95

ECHO POWER MICROPHONE or 148 GTL ST

CA-79

$69.95

High Performance, Magnetic Mount Antenna. 
Spring Base, Tunable and 1,000 watt Capacity

ATW-400

$39.95

DC POWER CORD Exact replacement power cord 
for 148 GTL ST

426-011-N-001

$7.50

MOUNTING BRACKET  Replacement  for 148 GTL ST

250-044-N-001

$4.50

MOUNTING BRACKET SCREWS 
for 148 GTL ST

634-188-9-001

$.25 ea.

COBRA CB RADIO ACCESSORIES

If you wish, you can order directly from Cobra

Order by phone:
Call 1-773-889-3087 (Press 1 from the main menu) 8a.m.-8p.m. M-F CST.
Order by mail or fax: Please fill out order form below, and mail/fax
directly to Cobra.

Fax to: 

1-773-622-2269

Please print clearly:

Name

Address (Not P.O. Box)

City                      

State

Zip

Telephone No.  (            )

Credit Card No.

Exp. Date

Customer Signature

Circle One:

Visa

MasterCard

Discover

Allow 4 to 6 weeks for deli very. Offer valid in Continental U.S. only.

★★

Illinois residents add 7%

★★

Cook Co. residents add .75% (7.75% total)

★★

Chicago residents add 1% (8.75% total)

★★

Indiana residents add 5%

★★

Michigan residents add 4 %

★★

Minnesota residents add 6%

★★

Ohio residents add 6%

★★

Wisconsin residents add 5%

Amount

(Tax if applicable )  

Shipping//handling         $3.75

Total 

Mail to:

Cobra Accessories Dept.

6500 W. Cortland St., Chicago, IL 60707

26

Prices subject to change without notice.

NOTES

148.GTL.ST.MANUAL  10/1/98 10:56 AM  Page 29