Guide :Radio Communications : 148 GTL 120-Channels Base CB Radio

No AM carrier or modulation. SSB transmits good

I am receiving and transmiting on SSB, but have no carrier signal or modulation on AM. What can I do? I have searched an repaired cold solder joints and checked final on side board near coax connector. It was ok.

Research, Knowledge and Information :

What is Amplitude Modulation | AM Tutorial | Radio ...

Single sideband: Amplitude modulation in the form of single ... its advantages can be used to good ... AM : DSB full carrier : A3E : Single sideband ...
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Amplitude modulation - Wikipedia

Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave.
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Single-sideband modulation - Wikipedia

... single-sideband modulation (SSB) ... is a type of modulation, used to transmit information, ... (or full-carrier) SSB or amplitude modulation equivalent ...
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4 Amplitude Modulation (AM)

4 Amplitude Modulation (AM) ... 4.5 Single-Sideband AM (SSB) ... 4.3 Double-Sideband Large Carrier AM 4.3.1 Modulation
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Amplitude Modulation - - Root Page

Single Sideband Modulation (SSB-AM) ... used to transmit data. ... Single Sideband Modulation (SSB-AM) In DSB-SC the carrier was suppressed as it was carrying no ...
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SSB Transmit Power: Audio Required! - Ham Radio

SSB Transmit Power: Audio Required! ... What’s going on with SSB transmit power? Modulation. ... SSB is a form of AM that has the carrier suppressed.
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N2CKH Amateur Radio Software&#153

... these radios were designed for SSB, to make them sound good on AM they ... a full Carrier and USB on transmit ... good reading is Amplitude Modulation ...
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Modulation Methods SSB and DSB - North Country Radio Home Page

Modulation Methods SSB and DSB ... is a type of AM without the carrier and one ... balanced mixer assemblies inherent suppression is good enough and no adjustment
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Suggested Questions And Answer :

Cobra 200gtl High Power Transmit problem??

Depending on the type of power supply, radio frequency (RF) energy from the transmitter may be 'fooling" it into thinking that you're overloading it. Check to see if there's any discernible dimming of the meter lamp when this problem occurs, if so, the supply is the culprit.Otherwise, its probable that the final amplifier transistors are overheating, either they are 'leaky' or not properly attached to the heat sink.
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No AM carrier or modulation. SSB transmits good

Great now check TR42 AM POWER then check TR41 AM POWER REG. They are on right side twards rear of board with front of radio faceing you part side up. A good place to start!
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142 GTL Good AM Carrier Weak Modulation????

Have you checked TR 26 AMC amp, and TR 24 & 25 AMC amps also for SSB TR34 ALC amp. make sure all voltages are right if all checks out try lifting out of the board or cut the collector of TR24 and try it. oop's that slipped out.
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Not transmitting good at all on ssb the power come back

Did you have your radio "peaked?" If you turn a Cobra Sideband radio up to much it may be great for the AM side but can crush the Sideband side. Make sure it is on frequency too. Use a frequency counter to check. Make sure your SWR is 1-1:5 and no higher than two. You may have to take it to a tech and have them but it on a scope.
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Corba 2000GTL # 53003909 Low are no transmit.. Bought off E-Bay...Had factor hand mic..Has extra channel witch are selected at the sp1 and sp2 selector switch.Both meter were stuck,It would transmit at first light would dim during modulation,and would cal in swr mod.Repace both meters clean up board.Seem to quit transmiting,so replace mic with turner plus 3. Receive well and shows modulation on am,but doesnt seem to trasmit any more.Radio will power up with power switch in the off postion if Turner three mic is in Electonic position at selector switch.

The problem with these radios (I have owned 4 of them and also repaired them) is that if they were "tweaked" too high several bad things can happen.If you have both AM and SSB transmit but it is very low output--suspect either the Driver or Final transistor are bad. You will need to unsolder all three leads (ECB) on each transistor and test them with a ohm meter.If either is bad----replace both--also note which transistors are in the radio--some people will replace them with "higher" output transistors to get more output. If the radio had modifications for a carrier control---it would only affect output on AM.The weak point in this radio if it has been tweaked is the voltage regulator IC located on the right wall of the set next to the audio output IC chip.Checking voltages will not really tell you very much---Confirm first the actual condition of Driver and Final transistors. Some good advice would be if replacing them restores transmit instantly lower both AM and SSB output either with the controls or by alignment of the driver and final stages of the radio.The fact that the radio was dimming the meter lights before is a dead giveaway that the radio was pulling maximum voltage from the regulator IC in the radio's power supply.Something else you may want to try that may or may not confirm this is switch the switch on the back of the radio and connect it to the DC power socket----IF RADIO WORKS THAT WAY-internal power supply is damaged and not the Driver/Final stage.Let me know what you find.SD TECH
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Cobra 140 gtl no modulation on am and ssb - Cobra 148 GTL 120-Channels Base CB Radio

Replace AM regulator transistor 2SA1012 !
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Cobra 140 gtl no modulation on am or ssb - Cobra 148 GTL 120-Channels Base CB Radio

Try another mic or check the mic connectionbernard
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Adjust modulation pot cb

4 watts on am and 12 on ssb the modulation pot isn't going to help you . go to and get the service manual.
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148 gtl receive works fine transmit has no power

If your receive is good and when you key the mic the meter goes to almost possitive your final is bad. Try it on side band usb/lsb if it transmitts good its the am final or driver.
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