Cobra 148GTL-DX User manual

Cobra 148GTL-DX
120-Channel
Solid State, Citizens Band
SS B CW AM FM 2-Way
Mobile Radio
Cobra Communications Product Group
DYNASCAN CORPORATION
6460 . Cortland Street
Chicago, Illinois 60635

Instruction Manual
for
Cobra 148GTL-DX
120-Channel
Solid State, Citizens Band
SSB CW AM FM2-Way
Mobile Radio
о
s
Cobra Communications Product Group
DYNASCAN CORPORATION
6460 . Cortland Street
Chicago, Illinois 60635

TABLE OF CONTENTS
Page
Section I: Introduction
Frequency Range...................................................................... 4
Section II: Spécifications.....................................................................................6
Section III: Installation
Location................................................... ................................... » ............ - -8
Mounting the Connection .................................................... 8
' IgnitionNoise Interférence . ............................................................. .9
Antenna ................ ..................... ........................................ .. .9
Tuning the Antenna for Optimum SWR.......................................................10
Base Station Operation.............................................................. 11
External Speaker. . ....................................................................... .. .11
Section IV: Operation
Controls and Iridicators ................................................................................ 12
A. Control Functions ..................................................................................... 12
B. Indicator Functions ...................................... ............................14
Operating Procedure to Receive .......... .......................................... 14
Operating Procedure to Transmit.............................................................. 15
Receiving SSB signais . ............. ........................................... 15
Operating Procedure to CW MODE .............................................................. 17
Roger Веер ........... ........................................................................................17
Alternate Microphones and Installation ............................................... 18
Section V: Maintenance and Adjustment............................................. 21
Section VI: Appendix
Ten Code; ............. ........................................................................................ 22
A Few Rules That Should Be Obeyed ...................... .23
How your CB Can Serve You ................................................ .. . . . ............ 24
Use Channel 9 for Emergency Message Only .................... .. ................. .. . 25
Warranty Service Instructions . ............................ ................. .. ......................... 26
Limited One Year Warranty......................................... ............... .. . t ............. 27
-2-

THECBSTORY
The Citizens Band lies between the shortwave broadcast and 10-meter
amateur radio bands, and was established by law in 1949. Two-way communica
tions service was opened in 1959.
HAVE
A GOOD DAY
TODAY
AND
A BETTER DAY
TOMORRO !
- 3 -

Section I
Introduction
FREQUENCY RANGE
The COBRA 148GTL-DX transceiver représente one of the most advanced
SSB CW AM FM two-way radios ever designed for use as the Citizens Radio
Service. This unit features advanced Phase Lock Loop (PLL) circuitry, which is
used in the AM FM mode, in the upper and lower single sideband modes and in
the CW mode providing complété coverage of ail 120 channels shown below.
CORRECTION
CHANNEL LOW BAND MID BAND HI BAND
1 . , 26.515 26.965 '■ 27.415
2 .525 .975 .425
3 .535 .985 .435
4 .555 27.005 .455
5.565 .015 .465
6 .575 .025 .475
7 .585 .035 .485
8 .605 .055 .505
9.615 .065 .515
10 .625 .075 .525
11 .635 .085 .535
12 .655 .105 .555
13 .665 .115 .565
14 .675 .125 .575
15 .685 .135 .585
16 .705 .155 .605
17 .715 . .165 .615
18 .725 .175 . .625
19 .735 .185 .635
20 .755 .205 .655
21 .765 .215 .665
22 .775 .225 .675
23 .805 .255 .705
24 .785 .235 .685
25 .795 .245 .695
-4-

CHANNEL LOW BAND MID BAND HI BAND
26 26.815 27.265 27.715
27 .825 .275 .725
28 .835 '■ .285 .735
29 .845 .295 .745
30 .855 .305 .755
31 .865 .315 .765
32 .875 .325 .775
33 .885 .335 .785
34 .895 .345 .795
35 .905 .355 .805
36 .915 .365 .815
37 .925 .375 .825
38 .935 .385 .835
39 .945 .395 .845
40 .955 .405 .855
The COBRA 148GTL-DX has a vastly superior receiver which includes an RF
gain control and noise blanker circuitry effective in both AM FM and SSB CW
modesr and- an aut=omatie-n0ise4knker-effective in the AM mode. The receiver
also features increased protection against cross modulation and strong adjacent
channel signais.
To obtain maximum performance from your transceiver, please read carefully
the following descriptions and operating instructions.
- 5 -

Section II
Spécifications
GENERAL
Channels
Frequency Range
Frequency Control
Frequency Tolérance
Frequency Stability
Operating Température Range
Microphone
120 FM, 120 AM, 120 LSB, 120 USB,
120 CW.
Low Band, 26.515 to 26.955 MHz.
Mid Band, 26.965 to 27.405 MHz.
Hi Band, 27.415 to 27.855 MHz.
Phase Lock Loop (PLL) Synthesizer.
0.005%.
0.001%.
-30°C to +50°C.
Plug-in dynamie; with push-to-talk switch
and coiled cord. , .
Input Voltage 13.8V DC nominal, 15.9V max., 11.7V min.
(positive or negative ground).
Transmit: AM full mod., 2.2A.
SSB 12 watts PEP output, 2Â.
Receiver: Squelched, 0.3 A.
Maximum audio output, 0.7A.
2-3 8 "(H) x 7-7 8"(W) x 9-l 4"(D).
5 lbs.
UHF, S0239.
Illuminated; indicates relative output power,
received signal strength, and SWR.
Size
Weight
Antenna Connector
Meter (3-in-l)
TRANSMITTER
Power Output AM FM CW, 5. watts.
SSB, 12 watts, PEP.
Modulation High-and low-level Class B, Amplitude Modu
lation: AM. Variable capacitance Frequen
cy Modulation: FM.
Intermodulation Distortion SSB: 3rd order, more than-25 dB.
5th order, more than -35 dB.
SSB Carrier Suppression 55 dB
Unwanted Sideband 50 dB
-6-

Frequency Response
Output Impédance
Output Indicators •
AM and FM: 450 to 2500 Hz.
50 ohms, unbalanced.
Meter shows relative RF output power and
SWR. Transmit LED glows red when trans
m iter is in operation.
RECEIVER
Sensitivity
Selectivity
Image Rejection
IF Frequency
Adjacent-Channel Rejection
AM FM and SSB CW RF
Gain Control
Automatic Gain Control
(AGC)
Squelch
ANL
Xoise Blanker
Voice Lock Range
Audio Output.Power
Frequency Response
Built-in Speaker
Extemal Speaker
(Not Supplied)
SSB CW: 0.25 jaV for 10 dB (S+N) N at
greater than й -watt of audio output.
AM: 0.5 ßV for 10 dB (S+N) N at greater
than Й-watt of audio output.
FM: 1.0 jaV for 20 dB (S+N) N at greater
than й-watt of audio output.
AM FM: 6 dB @3 KHz, 50 dB @9 KHz.
SSB CW: 6 dB @2.1 KHz, 60 dB @3.3 KHz.
More than 65 dB.
AM FM: 10.695 MHz Ist IF, 455 KHz 2nd
IF
SSB CW: 10.695 MHz.
60 dB AM FM & 70 dB SSB CW.
45 dB adjustable for optimum signal récep
tion.
Less than 10 dB change in audio output for
inputs from 10 to 100,000 microvolts.
Adjustable; threshold less than 0.5 ßV.
Switchable.
RF type, effective on AM FM and SSB CW.
Coarse (TX RX) ±7 KHz.
Fine (RX) ±1 KHz.
4 watts into 8. ohms.
300 to 2800 Hz.
8 ohms, round.
8 ohms; disables internal speaker when con
nected.
- 7 -

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
interfère with the driver or passengers in the vehicle. In automobiles, the trans
ceiver is usually mounted below the dash panel, with the microphone bracket
beside it.
Section III
Installation
MOUNTING THE CONNECTION
The COBRA 148GTL-DX 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 y ou. hâve determined the most convenient location in your vehicle, hold
the COBRA 148GTL-DX with mounting bracket irt the exact location de-
■ sired. If nothing will interfère with mounting it in the desired position,
remove the mounting bolts. Before drilling the.holes, make sure nothing will
interfère with the installation of the mounting bolts.
2. Connect the antenna cable plug to the standard réceptacle on the rear panel.
, Most CB antennas are terminated with a type PL-259 plug and mate with the
réceptacle.
3. Connect the red DC power input wire (with the fuse) to +13.8V DC. This
wire éxtends 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 ac
cessory contact on most ignition switches by tracing-the power wire from the
AM broadeast receiver 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 the right side of the transceiver or near the
transceiver, using two screws supplied. When mounting in an automobile,
place the bracket under the dash so the microphone is readily accessible.

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 installa
tions is from the generator and ignition system in the vehicle. Under most
operating conditions, when signal level is adéquate, the background noise does
not présent a serious problem. Also, when extremely low level signais are being
received, the transceiver may be operated with vehicle engine tumed off. The
unit requires very little current and therefore will not sigmfîcantly discharge the
vehicle battery.
Even though the COBRA 148GTL-DX has ANL and NB Controls, in some
installations ignition interférence may be high enough to make good communi
cations impossible. The electrical noise may corne 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 locating 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 installa
tions (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 attractive, compact and adéquate for applications where. the maximum
possible distance is not required. Also, the loaded whips do not present the
Problems of height imposed by a füll 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 ah practical purpose, however, the
radiation pattern is nondirectional. The slight directional characteristic will be
observed only at extreme distances. A standard antenna connector (type SO
239) 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 necessa'ry to run a
separate 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
regarding an adéquate grounding system and prévention of electrolysis between
fïttings in the hull and water.
-9-

TUNING THE ANTENNA FOR OPTIMUM SWR
Since there is such a wide vaiiety of base and mobile antennas, this section
will strictly concern itself to the various types of mobile adjustable antennas.
Because the abtenna length is directly related to the channel frequency, if
must be tuned to resonate optimally all 120 channels of the transceiver. Channel
1 requires a longer antenna than Channel 120 because it is lower in 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 a jusîment 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 148GTL-DX to Channel 21 @ Mid band. 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 continu-
ing to shorten the antenna you will notice the SWR reading will reach a low
print and then start rising again. This means that you have passed the opti
mum 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 @ Low band and
then to Channel 40 @ Hi band and compare SWR readings. They sould he
almost equal.
B. Antennas which must be eut to proper length.
1. Follow the same procedure as above, but adjust the length by cutting in 1 8"
incréments until a good match is obtained.
2. Be very careful not to eut too much at one time, as one it is eut, it сап п
longer be lengthed.
3. The whip is easily eut by filing a notch all the way around and breaking the
piece off with pliers.
--------------------------------- ------- NOTE -----------------------------------------
THE PROPER SETTING IS ACHIEVED WHEN THE SWR IS 1.5 OR
BELOW, AND WHEN IT HAS THE SAME READING FOR CHAN
NELS LOW BAND 1 AND HI BAND 40.
If you are having difficulties in adjusting your antenna, check the following:
A. AU doors must be closed when adjusting the antenna.
B. Make sure the antenna base is grounded.
C. Check your coaxial cable routing (it may be pinched when routed into the
car).
-10-

D. Try a different location on your car (keeping in mind the radiation pattern
youwish).
E. Is the antenna perfectly vertical?
F. Try a different location in your neighbortiood. Stay away from large metal
objęcts when adjusting (metal téléphoné or light posts, fences, etc.)
------------------------------------------ NOTE ----------- :-------------------------------
The COBRA 148GTL-DX will operate into an SWR of 2 to 1 indefmite-
ly and sustain an SWR of 20:1 for a maximum of 5 minutes at rated
operating conditions.
BASE STATION OPERATION
(Operating from 120V AC House Current)
To operate your transceiver from your home or office, using the regulär
house current as the power source, you will require the DYNASCAN Model CA-
20 Power-Pak which has been specially designed for the purpose. It is
available as optional equipment from your dealer. It consists of a precision-built
AC-DC power Converter that delivers the required power for the operation of the
transceiver. The CA-20 operates from any 120-volt, 60 Hz power source. Simply
connect the red (+) and black (-) leads of the transceiver to the, corresponding
terminais of the CA-20.
------------------ ---------------------- NOTE ----- ------------------------------------
Do not attempt to operate. this transceiver by connecting directly to
120 volts AC.
When the CA-20 Power-Pak is used with the transceiver for base station
operation, any Citizens Band beam, dipole, ground plane or vertical antenna may
be used. A ground plane vertical antenna will provide the most uniform horizon
tal coverage.
Extemal Speaker
The extemal speaker jack (EXT. SPK.) on the rear panel is used"for remote
receiver monitoring. The external speaker should have 8 ohms impédance and be
able to handle at least 4 watts. When the external speaker is plugged in, the
internal speaker is disconnected.
CW KEY
This jack is for Morse code operation; To operate, connect a CW Key to this
jack and place the CW FM AM USB LSB switch in the CWposition.
- 11 -

CONTROLS AND INDICATORS
There are thirteen Controls and three indicators on the front panel of your
COBRA 148GTL-DX.
Section IV
Operation
A, CONTROL FUNCTIONS
1. MIKE GAIN, (inner dual concentric) Ad justs the microphone gain in the
transmit and PA modes. This Controls the gain to the extent that fuli talk
power is available several inches away from the microphone.
2. OFF ON VOLUME (inner dual concentric). Turn clockwise to apply power
to the unit and to set the desired listening level. During normal CB opera
tion, the VOLUME control is used to adjust the output level obtained either
at the transceiver speaker or the extemal speaker, if used.
3. SQUELCH (outer dual concentric). This control is used to eut off or elimi-
nate receiver background noise in the absence of an incoming signal. For
maximum receiver sensitivity it is desired that the control be'Idjusted only
to the point where the receiver background noise or ambient background
noise is eliminated. Tum fully counterclockwise then slowly clockwise until
the receiver noise disappears. Any signal to be received 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 signais will be heard at a maximum clockwise setting.
4. RF GAIN CONTROL (outer dual concentric). Used to reduce the gain of
the RF amplifier under strong signal conditions.
- 12 -

5. SWR CAL CONTROL In order for you to ächieve maximum radiated po-
wer and the longest range, it is important that your antenna be in good
condition, properły adjusted and matched to your trans ceiver. The built-in
SWR (standing wave ratio) meter lets you easüy measure your antenna con
dition. To operate- this function, connect your antenna to the transceiver
antenna output connector. Select a channel near the middle pf 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 indicate'd on the meter face.
Then, without releasing the microphone button, switch the meter func -
tion switch to the SWR position and read the SWR indicated. The lower
the fifgure, the better, with 1 being ideal. Generally speaking, readings up to
3 are acceptable, but over 3 indicates that you are losing radiated power and
antenna adjustment may be advisable.
6. S-RF SWR CAL SWITCH. When in the S-RF position, the meter swings
proportionally to the strength of the received sighal. When transmitting, the
meter indicates relative RF output power.
When in the “CAL” position, the SWR meter can be calibrated by adjusting
the “SWR CAL” control to the. “CAL” mark on the meter'face. _ ___
When in the “SWR” position, the standing wave ratio is measured.
7. MODE (CW FM AM USB LSB) SWITCH. This switch is used to select CW,
FM, AM, LSB or USB mode of operation. Unless the station with which
communication is desired is equipped with SSB, the AM or FM mode is
normally used. The mode selector switch changes the mode of operation of
both transmitter and receiver simultaneously. Turn to “Receiving SSB
signais” for a further explanation of single sideband.
8. VOICE LOCK. Allows variation of the receiver operating frequencies above
and below the assigned frequency. Although this control is intended
primarily to .tune in SSB CW signais, it may be used to optimize AM FM
signais as described in the Operating Procedure paragraphs. Coarse operates
both TX RX but Fine only in RX.
9. CHANNEL SELECTOR. This switch selects any one of the forty Citizens
Band channels desired. The selected channel appears on the LED readout
directly above the Channel Selector knob.
10. CHANNEL 9 SWITCH. Channel 9 has been reserved emergenpycommunica
tions involving the immédiate safety of life of individuals or immédiate
protection of properly. Channel 9 may also be used to render assistance to a
motórist.
11. OFF-NB ANL SWITCH. In the NB ANL position, the RF noise blanker is
activated and automatic noise limiter in the audio circuits is also activated.
The RF noise blanker is.very effective for répétitive impulse noise such as
ignition interférence..
- ■ 13 -

12. TONE SWITCH-HI 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.
13. BAND SELECTOR. This switch selects HI, MID or LOW band of
operation.
В. INDICATOR FUNCTIONS
1. S-METER. Swings proportionally to the strength of the incoming signal.
2. RF METER. Swings proportionally to the RF output power.
3. SWR METER. Swings proportionally to the ratio of standing wave voltage
and RF output. Used to properly adjust the length of the antenna, and to
monitor the quality of the coaxial cable and all RF electrical connections. If
there is any dégradation whatsoever in any of the above, due to humidity, salt
spray, vibration or corrosion, the SWR meter reading will rise, thereby indi-
cating that a problem exists.
To calibrate, .switch to the “CAL” position transmit by pressing the mike
switch,^andWdju¥tAhWSWRWontroTto the “CAL” mark on the meter then
switch to “SWR” position for the SWR measurement.
4. CHANNEL INDICATOR. Numbered LED indicates the selected channel you
wish to operate on. LED indicates “9” when CH-9 is switched on.
5. RECEIVER 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.
6. PRESS-TO-TALK MICROPHONE. The receiver and transmitter are con-
trolled by the press-to-talk switch on the microphone. Press the switch and
the transmitter is activated, release switch to receive. When transmitting, hołd
the microphone two inches from the mouth and speak clearly in a normal
“voice”. The radios corne complété with low-impedance (500 ohm) dynamie
microphone. For installation instructions on o.ther microphones, see next
section, “ALTERNATE MICROPHONES AND INSTALLATION.”
OPERATING PROCEDURE TO RECEIVE
1. Be sure that power source, microphone and antenna are connected to the
proper connectors before going to the next step.
2. Tum unit on by tuning VOL control clockwise on COBRA 148GTL-DX.
3. Set the VOLUME for a Comfortable listening level.
4. Set the MODE switch to the desire mode.
-14-

5. Listen to the background noise from the speaker. Turn the SQUELCH con
tr ol slowly clockwise until the noise JUST disappears (no signal should be
present). Leave the control at this setting. The SQUELCH is now properly
adjusted. The receiver will remain quiet until a signal is actually received. Do
not advance the control too far, or some. of the weaker signais will not be
heard.
6. Set the CHANNEL selector switch to the desired channel.
7. Set the RF gain control fully clockwise for maximum RF gain.
8. Adjust the VOICE LOCK control to clarify the SSB CW signais or to opti-
mize AM FM signais.
OPERATING PROCEDURE TO TRANSMIT
1. Select the desired channel of transmission.
2. Set the MIKE GAIN control fully clockwise.
3. If the channel is elear, depress the push-to-talk switch on the microphone and
speak in a normal voice.
RECEIVING SSB SIGNALS
There are four types of signais presently used for communications in the
Citizens Band: FM, AM, USB, and LSB. When the MODE switch on your unit is
placed in the AM position, only standard double-sideband and in FM position,
only frequency déviation, full carrier signais will be detected. An SSB signal
may be recognized while in the AM or FM mode by its characteristic “Donald
Duck” sound and the inability of the AM or FM detector to produce an intel
ligible output. The USB and LSB modes will detect upper sideband and lower
sideband respectively, and standard AM signais.
SSB réception differs from Standard AM réception 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 side
band and no carrier is transmitted. The élimination of the carrier from the AM
signal helps to eliminate the biggest cause of whistles and tones heard on chan-
nels which make even moderately strong AM signais unreadable. Also, SSB takes
only half of an AM channel, therefore two SSB conversations wilFfit into each
channel, expanding the 120 AM channels to 240 SSB channels. The réduction in
channel space required also helps in the receiver bęcause only half of the noise
and interférence 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
- 15 -

may be understood if you consider that when modulation is applied to the
transmitter’s microphone in the USB mode, the transmit)er’s output frequency
is increased whereas in the LSB mode the transmitter’s output frequency is de-
creased. 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 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 résultant tone from
the receiver.
Thus when a vöice 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
necessary 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 perform
ing the same function as a phonograph speed control. When the speed is set to
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 simplici-
ty it is recommended that the AM modes be used to listen to AM signais.
- 16 -

OPERATING PROCEDURE TO CW(CARRIER WAVE) MODE
This is communicated by MORSE-CODE. This can be advantageously used
especially while channels in busy or communication in long distance.
1. TRANSMIT. Press CW KEY by MORSE-CODE switching Selector to CW
MODE and connecting CW KEY to CW KEY JACK. Your COBRA 148GTL-
DX transceiver is automatically changed from RX to TX when CW KEY is in
(MARK) and keeping the transmitting condition without being transmitted
MORSE-CODE during 0.15-second even if CW KEY is in (SPACE). And,
thereafter the unit is set in RX condition automatically. Be sure that the
CODE transmitted from your station is heard as monitor sound from internai
speaker (see Fig. 1).
I 1 i 2 i 1 i 2
« ► < -------
1 : MARK TX.
SIGNAL ON
TX.
NO SIGNAL
RX
'•"CAUTION : 1. MARK when CW KEY is closed.
2. SPACE when CW KEY is opened.
2. RECEIVE. Adjust FINE CONTROL of VOICE LOCK for your desired sound
when your transceiver is received MORSE-CODE Signal.
ROGER ВЕЕР
When this switch is placed in the ROGER ВЕЕР position, your radio auto
matically transmits the audio sign at the end of your transmission. The listener
can note easily that your transmission is over through the sign. Please note that
this ROGER ВЕЕР transmits 0.15-second at the moment PRESS-TO-TALK
SWITCH KNOB is off.
PRESS-TO-TALK OFF

ALTERNATE MICROPHONES AND INSTALLATION
For best results, the user should select a low-impedance dynamie type micro
phone or a transistorized microphone. Transistorized type microphones hâve a
low output impédance characteristic. The microphones must be provided with a
five-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 grounding and fifth is
for transmit control.
The microphone should provide the fonctions shown in schematic below.
4WIREMIC CABLE
Pin Number
1
2
3
4
Mic Cable Lead
Audio Shield
Audio Lead
Transmit Control
Receive Control
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.
2. Ail leads shoudl be cut to the same length. Strip the ends of each wire 1 8"
and tin the exposed wire.
Before begining the aefoal wiring réad carefolly, the circuit and wiring infor
mation provided with the microphone you select. Use the minimum head re-
quired in soldering the connections. Keep the exposed wire. lengths to a mini
mum to avoid shorting when the microphone plug is reassembled.
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1. Remove the retaining screw.
2. Unscrew the housing from the pin réceptacle body.
3. Loosen the two cable clamp retainer screws.
4. Feed the microphone cable through the housing, knurled ring and washer as
shown Fig. 4.
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
réceptacle 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 ré
ceptacle body сап be held in a stationary position by inserting it into the
microphone jack of the front panel. The numbers of the pins of the micro
phone plug are shown in Fig. 5, as viewed from the back of the plug. Before
soldering the wire to the pins, pre-tin the wire réceptacle of eàch pin of the
Plug.
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